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Rumors => Lenses => Topic started by: Tristan944 on December 03, 2012, 07:33:55 PM

Title: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 07:33:55 PM
Why are so many people confused about the focal length(s) of APS-C lenses? For example, I have the Canon 18-135mm APS-C lens. For some reason, people think that you have to multiply it by 1.6 for the "correct" focal lengths of 29-216mm. The conversion factor does not apply to APS-C-only lenses. If an APS-C-only lens says its 18-135mm, then it is 18-135mm. If an APS-C-only lens says its 57mm, then its 57mm. Even B&H, in the product description, makes the error by saying its equivalent to 29-216mm.
Title: Re: APS-C lens mm are correct
Post by: cinema-dslr on December 03, 2012, 08:24:07 PM
That isn't true.
if you want to have the same field of view with a crop and a FF and your using your ef-s lens at 18mm you'll have to put an 28,8 lens on the FF for the same picture.
and  a FF 18mm will give you the same field of view on your crop as an ef-s 18mm lens will.

I shoot with an 7d and have  ef-s and FF lenses
Title: Re: APS-C lens mm are correct
Post by: preppyak on December 03, 2012, 08:47:27 PM
The conversion factor does not apply to APS-C-only lenses. If an APS-C-only lens says its 18-135mm, then it is 18-135mm. If an APS-C-only lens says its 57mm, then its 57mm. Even B&H, in the product description, makes the error by saying its equivalent to 29-216mm.
You are both completely correct, and completely wrong. Focal length is focal length is focal length (except 18mm is usually an estimation on what may really be 17.4 or 18.8, etc). 18mm is 18mm for the lens. So you are correct that the 18-135 is 18mm and 135mm just like the 24-105 is 24mm and 105mm.

Where you are wrong is that all lenses have their apparent focal length impacted by the crop factor of the camera. So, any lens (even EF-S) that you put onto an APS-C body will be multiplied by 1.6. Any lens you put on a 4/3 camera will be multiplied by 2x, and so on. The EF-S stands for small image circle, meaning the lens is designed to only work for an APS-C field of view without vignetting, which allows them to make it smaller and lighter.

Canon itself confirms this in discussing the EF-S 18-55: http://www.canon.com/camera-museum/tech/report/200401/200401.html (http://www.canon.com/camera-museum/tech/report/200401/200401.html)
Quote
Wide zoom range (eqv. to 29-88mm in 135-format)

To design a lens that would appear to be 18mm on an APS-C camera, you would have to create an 11mm lens. Thus why all the EF-S designs tend to mimic the popular EF focal lengths (55-250 mimics 100-400, 10-22 mimics 16-35, 17-55 mimics 24-70 or 24-105, and so on)
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 08:47:43 PM
You are confusing it like other people do. You saying what the focal range would be if the 18-135mm lens were put on a full frame body. But here is your error, you can't put APS-C-only lenses on a full frame body. The 18-135mm CANNOT be attached to a full frame body like the Canon 5D. It can only be put on a APS-C body. Therefore, calculating the crop factor of what it "would" be on a full frame body is irrelevant. The only thing that matters on an APS-C-only lens is the stated focal range, in this instance, the 18-135mm. The focal range for this lens will never need to be recalculated for a full frame camera, because you cant even mount it on a full frame camera. Thats why so many people get confused and automatically multiply it by 1.6. Its 18-135mm, thats it.

Consider this scenario. The view and angle through the viewfinders for the following two scenarios will be identical:
Canon 7D with the 18-135mm zoomed to 18mm.
Canon 5D with an 18mm Full Frame only lens.

If you had no idea what camera I handed you, and gave you these two configurations, the image through the viewfinder would be identical and you wouldn't know which configuration I gave you. The 7D with the 18-135mm at 18mm will not be more "zoomed" in at "29mm". If the lens is at 18mm, then its at 18mm. If its at 135mm, its at 135mm.

The only time this changes is when a lens that is compatible with full frame cameras is put on an APS-C body. Then you multiply the focal length(s) by 1.6.
 
Title: Re: APS-C lens mm are correct
Post by: tnargs on December 03, 2012, 08:53:57 PM

Consider this scenario. The view and angle through the viewfinders for the following two scenarios will be identical:
Canon 7D with the 18-135mm zoomed to 18mm.
Canon 5D with an 18mm Full Frame only lens.
 

Sorry, that is 100% wrong.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 03, 2012, 08:56:07 PM
Consider this scenario. The view and angle through the viewfinders for the following two scenarios will be identical:
Canon 7D with the 18-135mm zoomed to 18mm.
Canon 5D with an 18mm Full Frame only lens.

If you had no idea what camera I handed you, and gave you these two configurations, the image through the viewfinder would be identical and you wouldn't know which configuration I gave you.

100% WRONG.

In that scenario (EF-S lens at 18mm on APS-C vs. EF lens at 18mm on FF), the FF viewfinder (and captured image) would show a much wider angle of view.

If you are at 18mm on APS-C and 29mm on FF, then what you see in the VF will be the same.
Title: Re: APS-C lens mm are correct
Post by: preppyak on December 03, 2012, 08:58:06 PM
You are confusing it like other people do. You saying what the focal range would be if the 18-135mm lens were put on a full frame body.
Actually, that's also not true (this example is APS-H): http://www.flickr.com/groups/canondslr/discuss/72157604422834954 (http://www.flickr.com/groups/canondslr/discuss/72157604422834954)

The reason you wouldn't traditionally use EF-S lenses is two-fold. One, they are lower quality than their full-frame equivalents, and often a similar price (17-55 and 24-105 are close, 10-22 and 17-40 are close, etc). And, because the EF-S lenses aren't designed to cover the full-frame or APS-H image circle. So using them at their widest settings will create severe vignetting (a literal black circle) and may cause them to hit the mirror. But, it's doable. You can use a 10-22 at about 15-16mm, much like you can use the Tokina 11-16 at about 15-16mm on Full-Frame. You can use them at about 12-13mm on APS-H. The crop factor applies in all cases, of course. The below example is the 10-22 on full-frame, APS-H, and APS-C by image box. Remember that images get sharper when you use the center of the glass. So you can see why APS-C use of the 10-22 would be good (no vignetting, not using extreme corners) and full-frame would be awful (unless you like circle mattes)

(http://daniel.nordling.nu/foto/EF-S-10D/EF-S-10-22-12mm-ff.jpg)

So, I could use an EF-S lens on full-frame if I wanted to; but I like my photos to not be mostly black
Title: Re: APS-C lens mm are correct
Post by: tnargs on December 03, 2012, 09:01:41 PM
preppyak, the 17-55 and 10-22 are at least as good and probably better than 24-105 and 17-40 in terms of IQ. EF-S rules!
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 03, 2012, 09:06:31 PM
Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane. Focal length is the distance from the rear nodal point (an optical point that may or may not be within the physical space of the lens) and the image plane.  An APS-C sensor samples a smaller portion of the image circle, so it will give a narrower AoV than a FF sensor. EF-S lenses project a smaller image circle, sufficient for APS-C but insufficient for FF - but that doesn't change their focal length.

preppyak, the 17-55 and 10-22 are at least as good and probably better than 24-105 and 17-40 in terms of IQ. EF-S rules!

Not exactly. They are better if you are talking about using all of them on the same APS-C body. But if you compare the EF-S lens on APS-C to the L lens on FF, the latter will deliver better overall IQ (although worse in some measures, especially distortion).
Title: Re: APS-C lens mm are correct
Post by: preppyak on December 03, 2012, 09:07:49 PM
preppyak, the 17-55 and 10-22 are at least as good and probably better than 24-105 and 17-40 in terms of IQ. EF-S rules
I'm assuming I own a 5d mark II in this scenario, in which case, the 10-22 and 17-55 would probably not be better for my purposes in terms of sharpness/vignetting/being a pain in the a** to deal with
Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane.
There we go, that's an even better way to state it
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 09:08:16 PM
I've done it myself. I took a picture with the following configuration and the pictures were identical.

Canon 7d with 18-135mm lens at 35mm.
Canon Rebel (film, so full frame) with 35-80mm lens at 35mm.

Why did the picture turn out the exact same? Because the 18-135mm at 35mm is at 35mm on my 7D. Since this is an APS-C only lens, the stated focal length is correct. It was not "zoomed" in to 56mm. The picture was IDENTICAL to the Canon film Rebel at 35mm.

Do it yourself and be amazed.

Get an APS-C-only lens and sent it to XYmm on a crop body. Then, get a EF lens and set it to the same XYmm on a full frame body and the two images will be the same. (I understand that the image will be different if an EF lens at the same focal length will be different when put on an APS-C body). Trust me, do exactly what I said and you will see that I am correct.

Do it right now and report back.
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 09:17:39 PM
Also, think about this. If the 18-135mm lens is really 29-216mm, why didnt they just call it that? Remember, this lens will never be put on a full frame body, so the 1.6 crop factor is non-existent.

The only way you will see what I am talking about is if you do a crop body and full frame comparison. Put an EF-S lens on a crop body and a EF lens on a full frame at the same focal length as indicated on the lens, such as at 18mm and 18mm, or 50mm and 50mm, and the images will be the same.
Title: Re: APS-C lens mm are correct
Post by: Policar on December 03, 2012, 09:19:36 PM
I've done it myself. I took a picture with the following configuration and the pictures were identical.

Canon 7d with 18-135mm lens at 35mm.
Canon Rebel (film, so full frame) with 35-80mm lens at 35mm.

Why did the picture turn out the exact same? Because the 18-135mm at 35mm is at 35mm on my 7D. Since this is an APS-C only lens, the stated focal length is correct. It was not "zoomed" in to 56mm. The picture was IDENTICAL to the Canon film Rebel at 35mm.

Do it yourself and be amazed.

Get an APS-C-only lens and sent it to XYmm on a crop body. Then, get a EF lens and set it to the same XYmm on a full frame body and the two images will be the same. (I understand that the image will be different if an EF lens at the same focal length will be different when put on an APS-C body). Trust me, do exactly what I said and you will see that I am correct.

Do it right now and report back.

I don't know what to say, but you're the only person who's experiencing this. Everything everyone else is writing is both consistent and correct (even if there are arguments over semantics relating to focal length not being an absolute measure of field of view).

I had a 17-55mm on my t2i and a 17-40mm on my 5D III. Used both very frequently at 17mm.

One of them was a lot wider.

I'm sorry to be so blunt, but you're wrong. "Equivalent" doesn't mean the focal lengths are mis-marked and 35mm on the EF-S lens is the same as 35mm on the EF lens exactly; what equivalent means is it's the equivalent field of view in terms of what 135 film or a FF sensor would see.

If this were true, the 10-22mm would be the widest Canon lens available for any dSLR. But the 14mm f2.8 is wider on FF than the 10mm is on a crop body.

All focal length means is the distance from the focal plane at which the lens's optical center focuses at infinity. That distance and the size of the sensor determines the field of view.
Title: Re: APS-C lens mm are correct
Post by: ChilledXpress on December 03, 2012, 09:22:59 PM
I've done it myself. I took a picture with the following configuration and the pictures were identical.

Canon 7d with 18-135mm lens at 35mm.
Canon Rebel (film, so full frame) with 35-80mm lens at 35mm.

Why did the picture turn out the exact same? Because the 18-135mm at 35mm is at 35mm on my 7D. Since this is an APS-C only lens, the stated focal length is correct. It was not "zoomed" in to 56mm. The picture was IDENTICAL to the Canon film Rebel at 35mm.

Do it yourself and be amazed.

Get an APS-C-only lens and sent it to XYmm on a crop body. Then, get a EF lens and set it to the same XYmm on a full frame body and the two images will be the same. (I understand that the image will be different if an EF lens at the same focal length will be different when put on an APS-C body). Trust me, do exactly what I said and you will see that I am correct.

Do it right now and report back.


Wrong !!! You did it with a fakey camera then... I own both crops and FF and the do not behave this way. Yes, the are real cameras... XS, 7D, 5D2 and 5D3.
Title: Re: APS-C lens mm are correct
Post by: rj79in on December 03, 2012, 09:26:23 PM
Also, think about this. If the 18-135mm lens is really 29-216mm, why didnt they just call it that? Remember, this lens will never be put on a full frame body, so the 1.6 crop factor is non-existent.

Canon does just that ... Downloaded the screenshot from Canon's website regarding the 18-135 lens. It specifically mentions that the zoom range will be 29-216 in FF equivalent.

If what you were saying was correct then 10mm on a 10-22 would be 10mm right? Try shooting at 10mm and you would know what everyone is talking about.
Title: Re: APS-C lens mm are correct
Post by: Dark Reality on December 03, 2012, 09:29:07 PM
you might want to check and see that your settings were correct, because its more than possible, that you may have overlooked what you had set it to, and in amazement rushed to the forums with a new discovery.

That.. or you saying something you know not to be true and get excited by the responses, maybe?
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 03, 2012, 09:30:08 PM


Do it right now and report back.

No sorry didn't work. The FF body had image showed slightly over 2.5x the total area of the target I was using.

Rather than just telling you that you are wrong.
If need to figure out why there is a discrepancy in sizes this is it.
A Full Frame sensor is 24x36mm
A lens no matter what length focuses approximately the same size on either the FF or Crop Sensor
The 7D's sensor is 14.9x22.3 mm. The focused image being the same size the 7D only covers a smaller portion of the image. The FF sensor is 1.6x taller and 1.6 times wider so it only senses a smaller area of the focused light circle.

EF-S lenses and EF lenses for the most part an 18mm lens is an 18mm lens regardless. (less manufacturing discrepancies).

The relationship has nothing to do with the length of lenses. It is only a comparison of sensor size and FOV comparisons  between a Full Frame and Crop sensor with equal length lenses.
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 09:31:24 PM
If I'm wrong I'll be the first to admit it, I'm not a proud person. I will check it again right now and see if I had done it incorrectly.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 03, 2012, 09:33:39 PM
If I'm wrong I'll be the first to admit it, I'm not a proud person. I will check it again right now and see if I had done it incorrectly.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

Because it is only a relationship that they are showing. It is salesmanship to make you think you are getting 1.6 times as much of something.
Title: Re: APS-C lens mm are correct
Post by: preppyak on December 03, 2012, 09:36:31 PM
But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.
Because the lens IS 18-135 in focal length. 24mm on the 18-135 is the same as 24mm on the 24-105 when mounted on the same camera...because focal length doesn't rely on the sensor at all. But, focal length is just one part of the equation; the other being the sensor. A larger sensor leads to a wider field of view (and thus what seems to be a "longer" focal length on APS-C cameras).

APS-H has a 1.3x crop factor
Nikon APS-C has a 1.5x crop
Canon APS-C has 1.6x crop
4/3rd has a 2x crop
...the list goes on. Imagine how incredibly confusing it would be trying to mount an old Nikon 28mm AI lens onto a Canon APS-C body if that 28mm was just a marketing name for what the lens appeared to be on Nikon crop camera (this is the equivalen of Canon printing 29-216 on the lens). I'd have to divide by 1.5 and multiply by 1.6 to get what it would be, which is insanely confusing. The same would be true of people usign old Canon FD lenses on 4/3rds cameras (divide by 1.6, multiply by 2...it gets silly) But, since focal length is a fixed property regardless of sensor, they print that, because its standardized.
Title: Re: APS-C lens mm are correct
Post by: rj79in on December 03, 2012, 09:41:08 PM
If I'm wrong I'll be the first to admit it, I'm not a proud person. I will check it again right now and see if I had done it incorrectly.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

The reason why Canon doesn't do that is that the lens really is an 18-135 lens, i.e. when you are shooting the lens at 18mm, the lens is actually at 18mm. It is only that the "field of view" is "cropped". This field of view on a FF sensor would be achieved at an equivalent focal length of 29mm. That's why the APS-C are called cropped sensors.

Hope this helps!
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 03, 2012, 09:45:49 PM
Well brethren, the results are in, and I am humbled.

Test configuration:
Canon 7D with EF-S 18-135mm at 35mm (I looked at file data and confirmed it was at exactly 35mm)
Canon film Rebel with EF 35-80mm (just turned the lens to 35mm and looked through the viewfinder. Didn't need to take a picture)

Results: I was wrong. The Canon film Rebel was wider at 35mm with the EF lens than the 7D was at 35mm with the EF-S lens. How embarrassing. At least I learned something.
Title: Re: APS-C lens mm are correct
Post by: rj79in on December 03, 2012, 09:47:22 PM
If I'm wrong I'll be the first to admit it, I'm not a proud person. I will check it again right now and see if I had done it incorrectly.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

Because it is only a relationship that they are showing. It is salesmanship to make you think you are getting 1.6 times as much of something.

+1

The focal length doesn't change at all. You only appear to have an increased focal length because of tighter framing.
Title: Re: APS-C lens mm are correct
Post by: TexPhoto on December 03, 2012, 10:11:12 PM
I made up these photos for m,y photo club to show point of view of different focal lengths.  All taken from my balcony without moving the tripod.  I shot 15, 24, 50, 100, 200, 400, and 800mm with a 5D2, and a 7D, but only show 15, 50, and 800 below.  In the Photo below, FF is on the left, 7D 1.6X crop is on the right.

(http://farm9.staticflickr.com/8482/8243575870_e122f68c1a.jpg) (http://www.flickr.com/photos/12047900@N06/8243575870/)
Screen Shot 2012-12-03 at 10.58.56 PM (http://www.flickr.com/photos/12047900@N06/8243575870/#) by RexPhoto91 (http://www.flickr.com/people/12047900@N06/), on Flickr
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 03, 2012, 10:11:57 PM
APS-C lens mm are correct

Well, at least your thread title was correct.  ;)

Like I stated, focal length is an intrinsic property of the lens.  They don't print 29-216mm on the 18-135mm lens because that would be a lie.  The fact that the FF equivalent figures are used in marketing is partly because bigger sounds better (as pointed out above) and partly historical, when everyone was new to digital and coming from the original FF 'sensor' aka 35mm film.

Here's one more for you to wrap your head around, Tristan944: the 'crop factor' applies to aperture, too, in terms of depth of field for the same framing. Because of the narrower AoV with APS-C, to take the 'same shot' (e.g. fill the frame with a 6' tall subject), at any given focal length you must be further from that subject with an APS-C camera compared to FF. That increased distance means deeper DoF, by a factor of 1.6x (which is a linear measure, when converted to a base-2 log it's 1.3-stops).  So...the real FF equivalent of your 18-135mm f/3.5-5.6 lens would be a hypothetical 29-216mm f/5.6-9 lens (in terms of DoF; sensor size doesn't affect exposure, since that's determined by light per unit area of sensor, independent of sensor size). 
Title: Re: APS-C lens mm are correct
Post by: insanitybeard on December 04, 2012, 07:22:20 AM
Not exactly. They are better if you are talking about using all of them on the same APS-C body. But if you compare the EF-S lens on APS-C to the L lens on FF, the latter will deliver better overall IQ (although worse in some measures, especially distortion).

Neuro, just out of interest, I realise that this is only one example so not applicable in general, but from what I have seen and read, my understanding is that the EF-S 10-22 does a better job at the wide end than the 17-40L does, with regards to resolution (specifically wide open corner resolution) and distortion.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 04, 2012, 02:15:15 PM
Not exactly. They are better if you are talking about using all of them on the same APS-C body. But if you compare the EF-S lens on APS-C to the L lens on FF, the latter will deliver better overall IQ (although worse in some measures, especially distortion).

Neuro, just out of interest, I realise that this is only one example so not applicable in general, but from what I have seen and read, my understanding is that the EF-S 10-22 does a better job at the wide end than the 17-40L does, with regards to resolution (specifically wide open corner resolution) and distortion.

That's actually why I emphasized 'overall'.  A current FF sensor will deliver more spatial resolution (measured in LW/PH) than a current APS-C sensor.  The extreme corners of the 17-40L at 17mm are an exception, but even at the borders (well away from the center, but not at the extreme corner), the 17-40 at 17mm f/4 delivers higher resolution than the 10-22mm does anywhere in the frame at any focal length and aperture. 
Title: Re: APS-C lens mm are correct
Post by: tnargs on December 04, 2012, 08:32:02 PM
at the borders (well away from the center, but not at the extreme corner), the 17-40 at 17mm f/4 delivers higher resolution than the 10-22mm does anywhere in the frame at any focal length and aperture.

I am probably being simplistic here, but the slrgear tests of those 2 lenses completely refute that claim. But they use 'blur index' which may differ from your strict term 'resolution'. My summary statement would be the 17-40 is a little less blurred in the border and corners than the 10-22's borders and corners at similar equivalent focal lengths and apertures.

They also show the 10-22 having the lower distortion in the 10-17mm range than the 17-40 has in the 17-30 range.

The 10-22 is a good lens, you paint it too shabby IMHO.
Title: Re: APS-C lens mm are correct
Post by: Axilrod on December 04, 2012, 09:50:30 PM
+1 for being completely wrong.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 04, 2012, 10:23:52 PM
The 10-212 is a good lens, you paint it too shabby IMHO.

Not my intent, sorry...the 10-22mm is a great lens, IMO.  Do note that I called out distortion specifically, that's notoriously difficult to control in a FF ultrawide lens, and much easier to control with the smaller elements used in an EF-S lens.

The EF-S 17-55mm, 15-85mm, and 10-22mm lenses all deliver optical performance that is on par with many L-series lenses, and in fact, those lenses all outperform 'sort of equivalent' L-series lenses when comparing both on the same APS-C camera (e.g. the 17-55mm is better than the 16-35L II and 24-105L when comparing all of them on a 7D - and I know this from both test charts and personal experience).  But when you put a different camera into the equation, and compare an EF-S lens on APS-C to an L-series lens on a recent FF/APS-H body, the larger sensor confers some IQ advantages.   So, for example, the 16-35L II on a 5DII will deliver better overall performance (although barrel distortion is definitely worse) than the equivalent framing of the 10-22 on a 7D (again, from both charts and my own real-world experience having used both combos).  The IQ of the 10-22mm in the 7D is already very good, it's just that the 16-35 + FF is slightly better.

You can see an aspect of that in the real world (sort of) with people who've popped off the rubber piece on the 10-22's lens mount and used it on a 1DIV - the 10-22 delivers images on the APS-H that are better than those from an APS-C body.
Title: Re: APS-C lens mm are correct
Post by: Hillsilly on December 04, 2012, 11:11:50 PM
Results: I was wrong. The Canon film Rebel was wider at 35mm with the EF lens than the 7D was at 35mm with the EF-S lens. How embarrassing. At least I learned something.

Darn - Was just about to pipe in with a possible explanation.  The 7D has 100% viewfinder coverage and magnification.  A lot of cheaper film cameras had less - generally around 90% with only 70% magnification.  This might have explained why they might have been perceived as similar.

But on thinking about it further, the 7D magnification would be based on the cropped image size, not a 35mm image size.  Maybe they wouldn't be similar at all.  I can understand why people find it confusing.
Title: Re: APS-C lens mm are correct
Post by: insanitybeard on December 05, 2012, 05:22:58 AM
Not my intent, sorry...the 10-22mm is a great lens, IMO.  Do note that I called out distortion specifically, that's notoriously difficult to control in a FF ultrawide lens, and much easier to control with the smaller elements used in an EF-S lens.

The EF-S 17-55mm, 15-85mm, and 10-22mm lenses all deliver optical performance that is on par with many L-series lenses, and in fact, those lenses all outperform 'sort of equivalent' L-series lenses when comparing both on the same APS-C camera (e.g. the 17-55mm is better than the 16-35L II and 24-105L when comparing all of them on a 7D - and I know this from both test charts and personal experience).  But when you put a different camera into the equation, and compare an EF-S lens on APS-C to an L-series lens on a recent FF/APS-H body, the larger sensor confers some IQ advantages.   So, for example, the 16-35L II on a 5DII will deliver better overall performance (although barrel distortion is definitely worse) than the equivalent framing of the 10-22 on a 7D (again, from both charts and my own real-world experience having used both combos).  The IQ of the 10-22mm in the 7D is already very good, it's just that the 16-35 + FF is slightly better.

You can see an aspect of that in the real world (sort of) with people who've popped off the rubber piece on the 10-22's lens mount and used it on a 1DIV - the 10-22 delivers images on the APS-H that are better than those from an APS-C body.

This interests me- does the FF sensor (or APS-H for that matter)- without getting too technical- deliver better IQ due to its larger area and greater light gathering ability (and presumably larger pixels) or does it also have something to do with the FF sensor utilising more of the surface area of the optics in the lens- hence APS-C sensors being more demanding on lenses because they focus the light through a smaller area of glass?
Title: Re: APS-C lens mm are correct
Post by: Random Orbits on December 05, 2012, 06:55:18 AM
This interests me- does the FF sensor (or APS-H for that matter)- without getting too technical- deliver better IQ due to its larger area and greater light gathering ability (and presumably larger pixels) or does it also have something to do with the FF sensor utilising more of the surface area of the optics in the lens- hence APS-C sensors being more demanding on lenses because they focus the light through a smaller area of glass?

The light gathering ability of the larger sensor helps especially with low light but the larger enlarging ratios associated with displaying pictures of the same size (screen or prints) is also a factor.  For lenses of the same generation and made from the same manufacturing technology, FF will win automatically because of its larger area (resolution based on line pairs/length).  APS-C will require sharper lenses to compete with FF to offset FF's larger area and smaller enlarging ratio.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 05, 2012, 08:17:09 AM
This interests me- does the FF sensor (or APS-H for that matter)- without getting too technical- deliver better IQ due to its larger area and greater light gathering ability (and presumably larger pixels) or does it also have something to do with the FF sensor utilising more of the surface area of the optics in the lens- hence APS-C sensors being more demanding on lenses because they focus the light through a smaller area of glass?

Mostly the former, And mostly due to the larger total area of the sensor, which gathers more total light.  Actually, performance at the edges of the image circle is worse on all lenses.   There is no differential advantage when comparing an EF lens on full frame to an EF-S lens on APS-C, but an APS-C sensor uses 'sweet spot' of an EF lens.
Title: Re: APS-C lens mm are correct
Post by: insanitybeard on December 05, 2012, 08:50:22 AM
Mostly the former, And mostly due to the larger total area of the sensor, which gathers more total light.  Actually, performance at the edges of the image circle is worse on all lenses.   There is no differential advantage when comparing an EF lens on full frame to an EF-S lens on APS-C, but an APS-C sensor uses 'sweet spot' of an EF lens.

I may have explained the point I was trying to make badly.... I know corner performance will always be worse towards the edge of the image circle and that using EF lenses on crop uses the centre portion of the image circle hence the sweet spot effect, what I was trying to say was:

 Is ultimate performance and resolution of APS-C going to be more limited than FF because the light is focused/concentrated through a smaller area of glass in the lens on APS-C than FF- ie, APS-C will start to show up limitations of the optics themselves before FF? (disregarding issues such as CA and drop in resolution away from the centre of the image circle which may be more pronounced on FF due to the larger image circle)

Even now I don't think I've explained myself well enough. Put another way, I guess I am trying to say that the optical glass has it's limitations and that if you are trying to focus light through a smaller area of that glass (as in APS-C) those limitations will become evident sooner?
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 05, 2012, 09:02:53 AM
This interests me- does the FF sensor (or APS-H for that matter)- without getting too technical- deliver better IQ due to its larger area and greater light gathering ability (and presumably larger pixels) or does it also have something to do with the FF sensor utilising more of the surface area of the optics in the lens- hence APS-C sensors being more demanding on lenses because they focus the light through a smaller area of glass?

The light gathering ability of the larger sensor helps especially with low light but the larger enlarging ratios associated with displaying pictures of the same size (screen or prints) is also a factor.  For lenses of the same generation and made from the same manufacturing technology, FF will win automatically because of its larger area (resolution based on line pairs/length).  APS-C will require sharper lenses to compete with FF to offset FF's larger area and smaller enlarging ratio.
If I am reading this correctly you are saying FF is better because it is larger than APS, therefor has less enlarging to reach a given size like 35mm against 6X7 ?

That's not the case, pixels are pixels. An 18MP FF image has just the same "enlargement" as a 18MP APS-C or DX or whatever. The advantage ( at least in theory) is that in the FF the pixels are larger and therefor should be able to record better information. However this advantage is being eroded with new technology. ( I know there are many other advantages, but "size" wise MP is MP.)
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 05, 2012, 09:17:12 AM
The new direction of this thread started with the comparison of the 10-22 to the 16-35 and the performance of a crop sensor wide.

The thing to keep in mind, for landscape and things wide the best performance is going to come out of the primes. The TSE 17's and 24 and the 24mm f/1.4L. Since there are no Canon primes made to mimic these primes range for a crop sensor, the FF will always be in the lead on the wide end if for no other reason (despite sensor quailty) being available glass.

It seems this thread is moving toward the high density 7D sensor vs the low density 5D II or III sensor debate.
Title: Re: APS-C lens mm are correct
Post by: Random Orbits on December 05, 2012, 09:27:49 AM
If I am reading this correctly you are saying FF is better because it is larger than APS, therefor has less enlarging to reach a given size like 35mm against 6X7 ?

That's not the case, pixels are pixels. An 18MP FF image has just the same "enlargement" as a 18MP APS-C or DX or whatever. The advantage ( at least in theory) is that in the FF the pixels are larger and therefor should be able to record better information. However this advantage is being eroded with new technology. ( I know there are many other advantages, but "size" wise MP is MP.)

So, if you have a 18 MP iphone camera (assuming it existed), that will give you the same enlargement ratio as a 18MP APS-C?  The enlargement ratio is based on final print size/sensor size.  To cope with the higher enlargement ratio, the smaller sensor needs to have a higher resolution/precision lens to compensate for the smaller sensor.
Title: Re: APS-C lens mm are correct
Post by: kubelik on December 05, 2012, 09:30:04 AM
tristan, it's possible that you had an amazing and lifelike dream where APS-C focal length indicators became not only true but also equivalent focal lengths.  I know I've had dreams where exceptionally awesome (but unfortunately unrealistic) things would happen, and I woke up really believing in them. 

it would be great to have all the APS-C standard zooms start at 18mm equivalent, rather than the current 29mm equivalent.  let's be honest, 29mm is only wide angle if you're a portrait shooter.  to a generalist, which most APS-C owners are, lenses should really be at least 25mm equivalent (16mm or wider focal length).  a 16-120 would be the same zoom ratio as an 18-135, and way, way more useful.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 05, 2012, 09:33:20 AM
Is ultimate performance and resolution of APS-C going to be more limited than FF because the light is focused/concentrated through a smaller area of glass in the lens on APS-C than FF- ie, APS-C will start to show up limitations of the optics themselves before FF? (disregarding issues such as CA and drop in resolution away from the centre of the image circle which may be more pronounced on FF due to the larger image circle)

No - what you're describing is purely an effect of pixel density, independent of sensor size (although it's generally true that comparing sensors of a similar generation, the APS-C sensor will have a higher pixel density).  From a resolution standpoint, a larger sensor will deliver higher resolution (in terms of line width/picture height) simply because the height of the picture is greater.

It seems this thread is moving toward the high density 7D sensor vs the low density 5D II or III sensor debate.

Agreed - let's not go there.   :-X
Title: Re: APS-C lens mm are correct
Post by: insanitybeard on December 05, 2012, 09:44:56 AM
Thanks all for the input.... Apologies for hijacking!
Title: Re: APS-C lens mm are correct
Post by: wjm on December 05, 2012, 10:34:32 AM

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

Like rj79in said: it is a 18-135 lens. A reason why people use the 1.6 factor is that they want to compare different lenses (the "field of view" mentioned before).

For example: I'm going on a city trip and I want to make some 'general' photo's. I probably want to bring and standard zoom. But what is a standard zoom? If I own a FF camera it is somthing like a 24-105, on a crop 15-85 and on a 4/3 something like a 14-50. I own a 5DII and use the range 24-28mm of my 24-105 a quite often in these situations. A also own a 40D as backup. When I would bring a 18-50 it would be no good (it starts at '28mm' compared to my 5DII with 24-105). I won't get the same "field of view".

With compact cameras the problem is even worse. The Canon S100 has a 5.2-26.0mm lens, the Canon A1300 has a 5.0-20mm lens. Which one is best for wide angle photography (IQ excluded)? One whould say: 5.0mm is wider then 5.2mm but sensor size is different in both cameras. Therefore you need the crop factor. These are about 4.6 for the S100 and 5.8 for the A1300, this gives a eqv. 24-120 and a 28-140 lens. So the S100 is 'wider'.
Title: Re: APS-C lens mm are correct
Post by: Renzokuken on December 05, 2012, 11:44:17 AM
I am amazed by the community here

questions like these with such a insistent and confident tone which is doomed to be false would initiate a series of "flaming" in other forum.

yet participants of this thread took great lengths to correct the thread-starter again and again politely even though he was not convinced with his mistake

kudos to everyone here
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 05, 2012, 12:12:26 PM
If I am reading this correctly you are saying FF is better because it is larger than APS, therefor has less enlarging to reach a given size like 35mm against 6X7 ?

That's not the case, pixels are pixels. An 18MP FF image has just the same "enlargement" as a 18MP APS-C or DX or whatever. The advantage ( at least in theory) is that in the FF the pixels are larger and therefor should be able to record better information. However this advantage is being eroded with new technology. ( I know there are many other advantages, but "size" wise MP is MP.)

So, if you have a 18 MP iphone camera (assuming it existed), that will give you the same enlargement ratio as a 18MP APS-C?  The enlargement ratio is based on final print size/sensor size.  To cope with the higher enlargement ratio, the smaller sensor needs to have a higher resolution/precision lens to compensate for the smaller sensor.

The final print size is related to the sensor "size", but in terms of enlargement, a sensor's size is defined by its digital information - mega pixels bits of information, not by its physical dimensions, as film would be. So yes, an 18MP iphone sensor would give an image the same size as an APS-C or FF or MF when viewed at 100%, that is when your computer program is adding in an equal amount of information in the viewed image. So in terms of enlargement of the displayed image, a 5D mk1 has to be "enlarged" more than a 7D despite the fact that the 7D's sensor is physically smaller.

However, you are quite right about the inability of a lens to resolve onto so many tiny pixels. Unclear information recorded by the very small chip will also result in your computer program not being able to add to the information clearly, resulting in a much poorer "enlargement".  Larger sensors have many many advantages over much smaller ones, but physical enlargement is not one of them - because they are not physically enlarged.

I know this is getting a little of topic, but it is surprising how many people think FF is better because it isn't enlarged as much as a smaller sensor ! Likewise many people don't realise that your computer is adding to the information. And I'm not sticking up for APS because I really dislike the "crop factor" effect for the sort of photography I do.
Title: Re: APS-C lens mm are correct
Post by: Chuck Alaimo on December 05, 2012, 12:36:21 PM
well damn, i was all ready to make some witty replies to the OP, but, you all beat me to the punch, and the OP beat me to his own punch too....lol

Wow though, gotta love how topics turn though!  Quite the surprise of info!  Go forum go!
Title: Re: APS-C lens mm are correct
Post by: Random Orbits on December 05, 2012, 01:38:42 PM
The final print size is related to the sensor "size", but in terms of enlargement, a sensor's size is defined by its digital information - mega pixels bits of information, not by its physical dimensions, as film would be. So yes, an 18MP iphone sensor would give an image the same size as an APS-C or FF or MF when viewed at 100%, that is when your computer program is adding in an equal amount of information in the viewed image. So in terms of enlargement of the displayed image, a 5D mk1 has to be "enlarged" more than a 7D despite the fact that the 7D's sensor is physically smaller.

However, you are quite right about the inability of a lens to resolve onto so many tiny pixels. Unclear information recorded by the very small chip will also result in your computer program not being able to add to the information clearly, resulting in a much poorer "enlargement".  Larger sensors have many many advantages over much smaller ones, but physical enlargement is not one of them - because they are not physically enlarged.

I know this is getting a little of topic, but it is surprising how many people think FF is better because it isn't enlarged as much as a smaller sensor ! Likewise many people don't realise that your computer is adding to the information. And I'm not sticking up for APS because I really dislike the "crop factor" effect for the sort of photography I do.

I think we are on the same page.  My original point was about the lens having to be of higher resolution on a crop than on FF to achieve comparable final resolution.  Keeping the MP constant for FF/crop makes that comparison simpler.

Most FF cameras (independent of the speed demons) have more MPs in general than their APS-C counterparts within the same brand, and I think the APS-C format is further along the MP/IQ curve than FF due to its higher density.  At some point, increasing density will not gain you anything due to optical/physical limitations.  If a FF camera and a crop camera had the same pixel density (akin to grain size of film), then there will be no advantage for a crop camera IQ wise, although other factors such as price, frame rate, etc. will still cause consumers to chose one over the other.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 05, 2012, 01:51:08 PM
I think if the rumored 7D II comes out, with the latest technology and a rumored 21mp sensor it may bring the FF vs Crop resolution MP density debate in to another level of sharp focus.

As it is right now there are only a limited number of possiblities and combinations that the discussion has any relavancy. In almost all but limited instances it is FF for the win.
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 05, 2012, 02:15:04 PM
Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane.


Yes, and that's why people who use the 50mm prime on their APS-C bodies and think they a using the traditional 85mm lens are mistaken.  What that have is a cropped 50mm image, not the more compressed image from a 85mm lens.  Also, an ef 35mm lens is not a standard 50mm lens on a crop.  It's a 56mm view with a 35mm lens' perspective. 
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 05, 2012, 02:20:17 PM
The final print size is related to the sensor "size", but in terms of enlargement, a sensor's size is defined by its digital information - mega pixels bits of information, not by its physical dimensions, as film would be. So yes, an 18MP iphone sensor would give an image the same size as an APS-C or FF or MF when viewed at 100%, that is when your computer program is adding in an equal amount of information in the viewed image. So in terms of enlargement of the displayed image, a 5D mk1 has to be "enlarged" more than a 7D despite the fact that the 7D's sensor is physically smaller.

However, you are quite right about the inability of a lens to resolve onto so many tiny pixels. Unclear information recorded by the very small chip will also result in your computer program not being able to add to the information clearly, resulting in a much poorer "enlargement".  Larger sensors have many many advantages over much smaller ones, but physical enlargement is not one of them - because they are not physically enlarged.

I know this is getting a little of topic, but it is surprising how many people think FF is better because it isn't enlarged as much as a smaller sensor ! Likewise many people don't realise that your computer is adding to the information. And I'm not sticking up for APS because I really dislike the "crop factor" effect for the sort of photography I do.

I think we are on the same page.  My original point was about the lens having to be of higher resolution on a crop than on FF to achieve comparable final resolution.  Keeping the MP constant for FF/crop makes that comparison simpler.

Most FF cameras (independent of the speed demons) have more MPs in general than their APS-C counterparts within the same brand, and I think the APS-C format is further along the MP/IQ curve than FF due to its higher density.  At some point, increasing density will not gain you anything due to optical/physical limitations.  If a FF camera and a crop camera had the same pixel density (akin to grain size of film), then there will be no advantage for a crop camera IQ wise, although other factors such as price, frame rate, etc. will still cause consumers to chose one over the other.
[/quote
+1. It's the quality of the recorded information that is the key, and traditionally FF or MF held this advantage, but the APS chips are closing the gap in IQ at low ISO.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 05, 2012, 02:41:01 PM
Just to get back on topic with this one: rather than stating APS-c lens mm are correct, when dealing with the field of view for a particular lens, it would be more accurate to state APS sensor size is incorrect. When using APS you've basically got a whole load of area missing around your frame  :'( problems with any wide (ish) field of view - which is why I don't like 'em !  ;D
Title: Re: APS-C lens mm are correct
Post by: Tristan944 on December 05, 2012, 09:27:23 PM
For what a fool I made of myself, you guys have been great. I'm glad I made the mistake because I never will again.

I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. I now know that the 18-135mm lens is an 18-135mm lens, but the camera and pictures being produced are not at 18-135mm, its at 29-216mm. Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him? Because zoomed out, its not showing 18mm, its showing 29mm. Telling me that it is 29-216mm lens would make more sense because that is what focal lengths are actually being used.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 05, 2012, 09:49:58 PM
Why do car dealers post the highway mileage on cars, when they know you live in the city and all of your driving will be in town?

Why do they call 2% milk 2% milk? In reality the regular milk you buy in the store has 4% fat, so in reality your only getting 50% less fat. Why don't they call it 50% less fat milk? (actually in small print the 2% milk in the frig says 37% less fat than whole milk, even more false advertising)

Same answer I think applies to your question?
Title: Re: APS-C lens mm are correct
Post by: cinema-dslr on December 05, 2012, 10:02:27 PM
For what a fool I made of myself, you guys have been great. I'm glad I made the mistake because I never will again.

I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. I now know that the 18-135mm lens is an 18-135mm lens, but the camera and pictures being produced are not at 18-135mm, its at 29-216mm. Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him? Because zoomed out, its not showing 18mm, its showing 29mm. Telling me that it is 29-216mm lens would make more sense because that is what focal lengths are actually being used.

being confused doesn't make one a fool  ;)
For a ef-s (aps-c only) lens it doesn't make much sense to call a 29-216 lens a 18-135 lens because that lens will never be put on a FF body.
but then the confusion starts when you put a 24-105L (FF) lens on a crop body eq  38-168mm.
The numbers on the lenses are correct you just have to multiply it by the crop factor. FF=1x aps-h=1,3x and aps-c=1,6x  :)

Title: Re: APS-C lens mm are correct
Post by: TexPhoto on December 06, 2012, 08:27:37 AM
Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane.


Yes, and that's why people who use the 50mm prime on their APS-C bodies and think they a using the traditional 85mm lens are mistaken.  What that have is a cropped 50mm image, not the more compressed image from a 85mm lens.  Also, an ef 35mm lens is not a standard 50mm lens on a crop.  It's a 56mm view with a 35mm lens' perspective.

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.  DOF will even be the same assuming they were taken at the same aperture.  And this applies for an image cropped in photoshop, or an image cropped via a smaller than FF sensor, or printed and cropped with scissors.

In the sample images I provided above, the 800mm photo is the same perspective and compresion of that part of the photo in the 50mm photo.  It has to be unless you move the camera.


Title: Re: APS-C lens mm are correct
Post by: emag on December 06, 2012, 10:30:43 AM
Ol' Paint is dead
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 06, 2012, 01:06:21 PM
The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 06, 2012, 01:13:52 PM
Simple  ;D
The perspective of pictures 2 and 3 is identical
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 06, 2012, 01:15:24 PM
The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.
Title: Re: APS-C lens mm are correct
Post by: florianbieler.de on December 06, 2012, 01:21:43 PM
I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. ... Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him?

The focal lenghts on the lens are correct! The values on the lenses are the actual focal lengths of the lenses, just because the sensor limits the field of view doesn't mean the focal length on the lens is wrong. Can you imagine how confused people would be if a crop sensor 17-50mm produced another field of view at 50mm than the EF 50mm - we somehow would see postings like why don't they print the actual focal lengths on the lenses ;)

It would be just way more complicated if you'd print crop sensor field of view focal length equivalents on crop sensor only lenses, and full frame field of view focal lengths on full frame lenses, as you can use these on your crop too. I vote for printing actual focal length and full frame equivalent if used on aps-c on the lens! Here comes the new Canon EF 17-50mm EF-S 27,2-80mm 2.8 IS II!  ::)
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 06, 2012, 01:34:15 PM
The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.
Title: Re: APS-C lens mm are correct
Post by: ahab1372 on December 06, 2012, 01:48:30 PM

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.
Yes, yes and yes. Distance only makes the perspective. The focal length and the sensor size determine the framing for a given distance from a subject.

As to the focal length equivalents: It is really a function of the sensor size, not of the lens. EF or EF-S doesn't matter. People/companies talk about the equivalent length to be able to compare how a lens on a certain camera feels in regards to the FOV, but they should really do so when talking about the camera, not the lens.
Title: Re: APS-C lens mm are correct
Post by: KyleSTL on December 06, 2012, 01:55:33 PM
The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.
An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.
From a framing standpoint, so long as the camera and all objects within the frame have not moved, the images will have identical perspective, with different depths of field (assuming the same aperture).  EDIT: Although at macro-like distances, that may change.  Neuro might have to chime in on that.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?
Yes, after applying distortion correction they will have identical perspective.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 06, 2012, 02:46:23 PM
The horse is dead but we go on;

As Perspective would apply to a picture;

"the technique or process of representing on a plane or curved surface the spatial relation of objects as they might appear to the eye; specifically : representation in a drawing or painting of parallel lines as converging in order to give the illusion of depth and distance"

Perspective as it would apply to you;

"the appearance to the eye of objects in respect to their relative distance and positions"

Thank you Merriam Webster

So would a picture taken at the same distance with two diffrent focal lengths have the same perspctive.
The wider lens would have contained in it, the ability to have the same perspective (illusion of depth and distance) as the long lens. However the picture with the long lens will not be able to give the same perspecitve (illusion of depth and distance) as the wide lens.

Choose your definitions and I believe most arugments so far can be made to fit.
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 06, 2012, 02:54:50 PM
But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 06, 2012, 03:04:46 PM
But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.
In this example perspective would indeed be different because your distance would be (very) different. Take the shot with 35mm from the same position as your 200, then crop 35mm in post to the same framing - perspective will be identical.

Title: Re: APS-C lens mm are correct
Post by: TexPhoto on December 06, 2012, 03:09:29 PM
Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 06, 2012, 03:11:31 PM
Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.
+1
Title: Re: APS-C lens mm are correct
Post by: Chuck Alaimo on December 06, 2012, 03:12:50 PM
Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.

doesn't lens curvature play into this too?  anything on the wide end has that bend to it, even if its at a distance right?  Isn't that due to the curvature of the lens, which is much more pronounced on wide angle lenses?  (also why wide angle tilt shifts are both specialized and pricey because they have comples systems inside to reduce curvature?)
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 06, 2012, 03:44:48 PM
But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

They would most likely be diffrent because of the depth of the background may appear diffrently, but maybe not. Since a picture is only creating an illusion of depth, if all things in the picture were of the same framing and the pictures were identical in appearance, then they would have the same perspective. Although you shot them from a diffrent perspective.
You are dealing with two diffrent things, what the picture shows and what your physical location is.
You can say your perspective changed, but it is still possible for the picture to have the same perspective.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 06, 2012, 03:59:16 PM
My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 06, 2012, 04:08:15 PM
My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.

Or shoot a perfectly flat wall with the 35mm at 10', and the 200mm picture would have the exact same perspective at 57.14'. However you will not have the same perspective.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 06, 2012, 04:22:24 PM
I think that to help clear this up a bit it is worth mentioning that in the practical application a 200mm does have a more compressed perspective than say a 20mm, because you have to be using the 200mm from much further away to achieve equal framing, that is assuming you are using the same sensor size !! :P
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 06, 2012, 04:32:40 PM
I think that to help clear this up a bit it is worth mentioning that in the practical application a 200mm does have a more compressed perspective than say a 20mm, because you have to be using the 200mm from much further away to achieve equal framing, that is assuming you are using the same sensor size !! :P

Excellent  :P

Now we can start a discussion on compression and how it affects ff vs crop framing and crop factor. Really though it might just part of the explanation for the diffrence in perspective.

Title: Re: APS-C lens mm are correct
Post by: Videoshooter on December 07, 2012, 01:19:28 AM
But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

That is because you changed the distance to subject in your example. If you stand in the same spot and take a photo of the same subject, the perspective will be identical with any lens, save for any distortion introduced by the lens (ie field curvature in a fisheye lens). Of course the framing will be very different, though cropping to the same framing will overcome this (though will not result in the best picture quality).

Apply this to a 50mm and 85mm lens, taking a portrait, and you get a perfect example of why we use equivalent FOV's. Put the 85mm lens on the FF camera, and take a photo. Now put your 50mm lens on that same camera and take another photo. The perspective will be exactly the same, but the framing is different - you have a whole bunch of extra area around the edges of the image. But, if you crop that 2nd photo to the same framing, it will have the exact same perspective as the first photo. Now, pair your 50mm lens with a APS-C camera. It will give the same photo (in terms of perspective and framing) as in photo 2, although it is already cropped straight out of the camera. The FOV will be the same (give or take a few mm), and the perspective will be the same, as the photo taken with the 85mm on the FF camera.

Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 07, 2012, 11:44:18 AM
My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.

Backing up is the ether.

(http://static.photo.net/attachments/bboard/00W/00Wqpm-259365584.jpg)
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 07, 2012, 11:49:13 AM
Having a new baby keeping me up at night is clouding my thinking.


EDIT: Does CR compress photos when I attach them to a thread?  The attached photo look great on my iMac and iPad. I think my monitor at work here is getting old (it's a $199 special from day one).
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 07, 2012, 12:20:30 PM
Daniel, I have to admire your tenacity !

Are you sure you didn't sneak a little further back for the APS-C shot - it is a little wider framed but this might be the focal length of the lens.

If nothing else the two pictures are a good example of how the modern 85L has improved contrast control and tones over the film era 50 1.4, which tends to have more abrupt highlights - but that's another topic altogether.

I assume you are showing the toy in the APS picture is smaller in relation to the child. If you were only a foot or so further away this would explain it. However, if you were not....................maybe we can open a complete new can of worms! I'm very short sighted, and without my glasses on things that are out of focus appear much bigger than when viewed in focus if I put my glasses back on. Could it be that on a very fast lens like the 85 1.2, the out of focus element looks bigger due to the blur ? As there is less focus blur with the 50, this could explain it.
Title: Re: APS-C lens mm are correct
Post by: Sporgon on December 07, 2012, 01:45:44 PM
Nice example privatebydesign. I presume the lady in the photo is trying to explain this over the phone to one of the doubters............. ;D
Title: Re: APS-C lens mm are correct
Post by: KyleSTL on December 07, 2012, 02:13:31 PM
Re. Perspective and focal length.

As a picture is worth a thousand words.

First comparison, 17mm lens and 200mm lens both on same camera from same place and both f8, these are the full images.

Second comparison, same images with the 17mm cropped to match the framing of the 200mm.

As you will see, whilst the dof is very different, the perspective (the size of the various elements within the frame with regards each other) stays constant. The woman, the trees and the jumps are the same size in both examples when the 17mm is cropped.

This is also a very graphic demonstration of why smaller sensors have deeper dof, the second image crop is effectively a small sensor shot with an 11 times crop factor, which still puts it way bigger than P&S's and phone cameras.
Not true, below are crop factors of various sensor sizes:

FF - 1x
APS-C (Canon) - 1.6x
m4/3 - 2x
Nikon 1 - 2.7x
1/1.7" - 4.6x
1/2.5" - 6.0x
1/3" - 7.2x
1/4" - 10.8x

I believe the iPhone sensor is in the ballpark of 1/3", for example.
Title: Re: APS-C lens mm are correct
Post by: sandymandy on December 07, 2012, 03:23:33 PM
I cant understand why this topic always gets discussed so much? a 50mm lens is a 50mm lens

A photo taken from the same position with a FF camera will look like it was taken with a 50mm lens. A photo taken with an APS-C will look like it was taken with an 80mm lens.

Thats all what the crop factor is about and its so easy and clear to understand, why gotta discuss so much?

Its just common to say "equivalent of blabla on APS-C". Maybe its just the wrong term used but so what? everybody knows what it supposed to mean.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 07, 2012, 03:26:59 PM
Its just common to say "equivalent of blabla on APS-C". Maybe its just the wrong term used but so what? everybody knows what it supposed to mean.

You'd think so, but >80 posts here and many other threads on the topic suggest otherwise...
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 06:09:16 PM
Re. Perspective and focal length.

As a picture is worth a thousand words.

First comparison, 17mm lens and 200mm lens both on same camera from same place and both f8, these are the full images.

Second comparison, same images with the 17mm cropped to match the framing of the 200mm.

As you will see, whilst the dof is very different, the perspective (the size of the various elements within the frame with regards each other) stays constant. The woman, the trees and the jumps are the same size in both examples when the 17mm is cropped.

This is also a very graphic demonstration of why smaller sensors have deeper dof, the second image crop is effectively a small sensor shot with an 11 times crop factor, which still puts it way bigger than P&S's and phone cameras.

I have to disagree, your definition of perspective only relates to the size of things in the picture. Since the two pictures obviously have a different depth of field the one shot with the 200mm creates a different illusion of depth and therefore a different perspective. At best you can say the elements in the picture are the same size once cropped. You can say that the pictures were shot from the same perspective, your perspective. But the pictures do not have the same perspective.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 06:16:27 PM
Its just common to say "equivalent of blabla on APS-C". Maybe its just the wrong term used but so what? everybody knows what it supposed to mean.

You'd think so, but >80 posts here and many other threads on the topic suggest otherwise...

What is amazing is that there are so many threads about it. Many people just use crop or ff not both. The reality of it is if  you use a crop camera and do not own a FF, the ratios and comparisons are meaningless to you. If you own a FF and do not use a crop it is meaningless to you. Yet it is important to debate what does not matter.

But then again this thread went through 3 pages of perspective talk.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 07, 2012, 06:31:46 PM
I have to disagree, your definition of perspective only relates to the size of things in the picture. Since the two pictures obviously have a different depth of field the one shot with the 200mm creates a different illusion of depth and therefore a different perspective. At best you can say the elements in the picture are the same size once cropped. You can say that the pictures were shot from the same perspective, your perspective. But the pictures do not have the same perspective.

Sorry, no. It's not his definition of perspective, it's THE definition of perspective.

Quote from: The Dictionary
perspective
|pərˈspektiv|
Noun
1. the appearance of things relative to one another as determined by their distance from the viewer

The fact that the objects in both images are the same size in relation to each other means the perspective is identical, by definition.  DoF has nothing to do with it, relative blur has nothing to do with it.

But then again this thread went through 3 pages of perspective talk.

...and with apologies, unfortunately it seems the point is still not clear to some.  ???
Title: Re: APS-C lens mm are correct
Post by: ahab1372 on December 07, 2012, 06:45:05 PM
And while we are at it: compression is also not a feature of the lens, but of the distance. It is actually included in Neuro's  THE definition of perspective.
If you are farther away, faces look flatter, no matter what lens you use.
Title: Re: APS-C lens mm are correct
Post by: TexPhoto on December 07, 2012, 07:24:29 PM
And while we are at it: compression is also not a feature of the lens, but of the distance. It is actually included in Neuro's I mean THE definition of perspective.
If you are father away, faces look flatter, no matter what lens you use.

Yes!  You don't even need a lens.  This effect can be seen with your eyes.  Close one eye and put the other an inch from someones nose.  (Maybe make sure this is  a friend).  Wow huge nose, fisheye perspective! 
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 09:02:00 PM

Sorry, no. It's not his definition of perspective, it's THE definition of perspective.


How would this definition not apply, this is from a simple google search of perspective (it appears at the top);

"The art of drawing solid objects on a two-dimensional surface so as to give the right impression of their height, width, depth, and...
A picture drawn in such a way, esp. one appearing to enlarge or extend the actual space, or to give the effect of distance."

Granted we are not drawing in the literal sense of the word, but we are creating the image. Is our work "art" or are we just capturing an image relative to the viewer.

Personally if we are using the perspective as it relates to the content of the picture itself, I prefer this definition as it adds the element of depth.

This one is from the Free Farlex Dictionary online;
"4. The technique of representing three-dimensional objects and depth relationships on a two-dimensional surface."
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 09:04:34 PM
...and with apologies, unfortunately it seems the point is still not clear to some.  ???

Crystal clear, I am just disagreeing with how we are using the word "perspective"
I think in a hobby we strive to create something that is considered art, we should use the definition that closely matches the one for art.  :)
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 07, 2012, 09:31:34 PM
I suppose I should have indicated that's THE definition for photographic imagery.

The point of the definitions that pertain to drawing (which are the definitions you reference) is that for proper perspective, the size relationships of the rendered objects must be appropriate to one another and relative to the distance at which they are apparently rendered, so that 3D space is correctly represented as 2D. With a photograph, that's already a given due to the direct capture of the image, which faithfully preserves spatial relationships at the distance from which the image is captured, so those definitions are irrelevant to photography. I'm not arguing that photography isn't art, but the definitions you reference aren't any more relevant to a photographic image than they are to music as an art form.

You can choose to believe differently, and I'm sure many will agree. But then, many people think alot is a word, and that doesn't make it correct.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 09:40:38 PM
From photonotes.org
Dictionary of Film and Digital Photography;

"Perspective.

Visual cues in a two-dimensional image which give the impression of three-dimensional space. Such cues include lines converging towards a vanishing point, aerial haze, different sizes of common objects, different zones of focus, etc."

I suppose there are alot of people that think this way.   ::)
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 07, 2012, 09:52:15 PM
From photonotes.org
Dictionary of Film and Digital Photography;

"Perspective.

Visual cues in a two-dimensional image which give the impression of three-dimensional space. Such cues include lines converging towards a vanishing point, aerial haze, different sizes of common objects, different zones of focus, etc."

I suppose there are alot of people that think this way.   ::)

I think you're still missing the point.  The definition above is what perspective is, not what determines perspective.   The point is that the only thing that determines perspective is distance.  Not focal length.  Not aperture.  Not subjective blur.  Distance, and only distance. 

In the examples posted by privatebydesign, the perspective is identical.  That is fact, and that is the point.  Of course, the images have a perspective - in the images, the woman's left arm looks as large in diameter as the as the tree trunk in the background.  Do you think her arm is really that big?  No, because she is closer than the tree trunk.  That's what perspective is.  But what determines that perspective is how far both she and the tree trunk are from the camera.  In both the cropped 17mm image and the 200mm image, her arm is the same relative size compared to the tree trunk.  That's because the shots were taken from the same distance - thus, the perspective is the same, and the relative sizes of her arm and the tree trunk clearly demonstrate that fact.  If privatebydesign had taken another shot at 17mm, this time matching the framing of 200mm without cropping, he'd have to be right next to her - and in that case, I'm sure you can envision that her arm would look much larger than the tree trunk.  That would be because the distance had changed, which would change the perspective.
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 07, 2012, 11:35:48 PM
Here's an example from the wiki page on perspective distortion (http://en.wikipedia.org/wiki/Perspective_distortion_(photography)), an example that illustrates some of this confusion:

(http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Focal_length.jpg/220px-Focal_length.jpg)

You see the different focal lengths printed on the images, and you see the relative sizes of the two water bottles changing, and you think that focal length is the reason.  Even the text in the caption of that image suggests the effect is due to focal length.  But consider...the pink bottle is the same height in all three images - therefore, as the focal length is reduced, the camera must have been moved closer to achieve the same framing.  It's the movement of the camera, not the change in focal length, that results in the different perspectives.

Let me try to illustrate what I mean with a similar set of examples, but where I first vary just focal length but not distance, and then vary focal length and distance.  Since I prefer beverages other than water, I selected a different pair of subjects for a similar test.

The two bottles are 18" apart, and the distances in the image below are measured from the sensor to the front bottle. All were shot at f/5.6.  As described above, it's normal for the bottle in front to look larger, that's perspective - objects that are further away look smaller, even though we know they are the same size.  Note that the bottle in front is the same height in all the images.

In the left column, the 50mm and 24mm shots were at the same distance as the 100mm images, and the images were cropped to match the framing of the 100mm image.  As you can see, the relative size of the rear bottle is the same in all the images.  The perspective is the same - the two bottles maintain the same relative size, despite the differing focal lengths.  The distance is the same, so the perspective is the same.

In the right column, which is equivalent to the water bottle shots from the wiki page, the 50mm and 24mm shots were taken at successively closer distances to the bottles, matching the framing to the 100mm shot by moving the camera.  As you can see, the relative size of the rear bottle gets smaller as the camera is moved closer.  Different perspective, because the distance is changing.  Comparing the side-by-side 50mm and 24mm images, you can see that with the same focal length but different subject distances, the perspective is different.

So, varying focal length alone, without changing distance, does not affect perspective.  As stated above (by me and others), perspective is determined by distance, and distance alone. 

As others pointed out above, 'telephoto' compression and 'wide angle' expansion distortion are the same phenomenon.  The reference to 'telephoto' and 'wide angle' there is misleading - it has nothing to do with the focal lengths, only the distance.  But longer lenses are usually used at longer distances, and wide lenses are usually used at closer distances (think of framing a person for a portrait), thus the erroneous association with a lens type when it's really the commonly used distances for those lenses that is the cause of both types of perspective distortion.

Regardless of whether or not this clarifies what determines perspective, I'm about to enjoy that bottle of Chocolate Stout.   ;D
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 07, 2012, 11:54:25 PM
 :) Go enjoy, I just finished typing this and I saw you had posted so I modified it a bit.

I understand what you are saying, and perspective is determined by distance. (reading your last post, perspective distortion definitely is).

We were just using the term perspective, which by the definitions I have read means a few more things.

My point has been the final two pictures that were created. The perspective in those two pictures, the visual cues give a different impression of the three-deminsional space. That being the dof and field and focused areas.
There are many more sites offering similar or the same as I quoted, definition of what perspective "IS" as it relates to photography. I haven't found anything saying this definition is incorrect.








Title: Re: APS-C lens mm are correct
Post by: ahab1372 on December 07, 2012, 11:58:10 PM

Regardless of whether or not this clarifies what determines perspective, I'm about to enjoy that bottle of Chocolate Stout.   ;D
Enjoy, You've earned it. :)
Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 08, 2012, 12:00:18 AM
We were just using the term perspective, which by the definitions I have read means a few more things.

Well, that's your  viewpoint  opinion  perspective on the issue...   :P :P :P
Title: Re: APS-C lens mm are correct
Post by: ahab1372 on December 08, 2012, 12:04:55 AM
:) Go enjoy, I just finished typing this and I saw you had posted so I modified it a bit.

I understand what you are saying, and perspective is determined by distance. (reading your last post, perspective distortion definitely is).

We were just using the term perspective, which by the definitions I have read means a few more things.

My point has been the final two pictures that were created. The perspective in those two pictures, the visual cues give a different impression of the three-deminsional space. That being the dof and field and focused areas.
There are many more sites offering similar or the same as I quoted, definition of what perspective "IS" as it relates to photography.
which IMHO is not a good thing, because the term becomes ambiguous, and it is not clear any more what people are talking about.
Quote
I haven't found anything saying this definition is incorrect.
That still doesn't mean it is widely accepted, and even if it was, it is still not correct. I prefer the less ambiguous definitions
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 08, 2012, 12:56:50 AM

That still doesn't mean it is widely accepted, and even if it was, it is still not correct. I prefer the less ambiguous definitions

Perhaps if we stuck with and used the term "perspective distortion" it would be less ambiguous and spot on, rather than a word that pulls up a half dozen different meanings when you word search. Kind of the point I was making, thanks.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 09, 2012, 12:33:19 AM
@privatebydesign

Perspective Distortion
Rectilinear Perspective
Vanishing Point Perspective
Height Perspective
Overlap Perspective
Dwindling Size Perspective
Atmospheric Perspective

A National Geographic photographers article on incorporating Perspective http://photography.nationalgeographic.com/photography/photo-tips/pbb-get-some-perspective/ (http://photography.nationalgeographic.com/photography/photo-tips/pbb-get-some-perspective/)

Here is an interesting one, a photography gallery that named there gallery after the distance they were from an object when they took the picture;

http://www.perspectivegallery.org/about-perspective-gallery- (http://www.perspectivegallery.org/about-perspective-gallery-)

My only point is that using just the word "perspective" has a bit broader meaning to many people in photography than the one offered. You may not like that, but it is true.




Title: Re: APS-C lens mm are correct
Post by: neuroanatomist on December 09, 2012, 07:17:26 AM
My only point is that using just the word "perspective" has a bit broader meaning to many people in photography than the one offered. You may not like that, but it is true.

And alot of people use alot of words irregardless of they're proper meaning.  That don't make them rite.  That be true to, even if we doesn't like it muchly.
Title: Re: APS-C lens mm are correct
Post by: Don Haines on December 09, 2012, 09:06:28 AM
Focal length of the lens is the same no matter which camera it is mounted on. The basic difference between full frame lenses and APS-c lenses is the size of the image circle. If we assume no problems hitting mirrors, we get the following:
Put a full frame lens on either camera and the image circle covers the entire sensor. Put an APS-c lens on an APS-c camera and the image covers the entire sensor. Put an APS-c lens on a ff body and you get severe vignetting.

The difference in field of view (sometimes called reach or apparent focal length) between ff and aps-c comes from the sensor, not the lens. To try to explain this, imagine a camera body where you could slide in and out two different sensors, one a ff sensor, and the other a 4/3 sensor. ( I picked 4/3 because it is 1/2 the size and the math is easy) both sensors are 10 Mpixels and we use the same lens, which has a 20 degree field of view.

When you use the ff sensor, light from that 20 degree field of view hits the edge of the sensor and is captured as the edge of the image.  When we slip in the 4/3 sensor, the same light as before enters the camera, but the smaller sensor only sees a portion of that light. The light that falls on the edge of the smaller sensor is now that light from the central part of the view, and what gets captured by the sensor is a 10 degree field of view. We look at the two images and we say that the 4/3 sensor image is like using twice the focal length because that's what the field of view looks like.

We are not cropping the image, what we are doing is sampling the view with a higher density of pixels for the central part of the image and ignoring the rest. If our ff sensor was 40Mpixels and we used just the center 10 Megapixels of the capture, the two resulting images would have been identical.

In the real world, things are not as clean. The smaller pixels, being smaller, are hit by less light, so the signal to noise level will be lower. That smaller pixel receives 1/4 the light as the FF pixel, so to give the same brightness in the output image, the gain of the sensor has to be turned up by a factor of 4 to compensate..... and this is where 2 stops of performance improvement of FF sensors comes from. It is harder (impossible?) to make a smaller pixel as good as a larger pixel so what you end up with is a series of trade offs.... And this is assuming our lens is perfect... Flaws in the glass will become more apparent with the higher sampling density.....

In ff vs APs-c you are trading pixel quality for pixel density. The real difference between the two is that the larger pixels of ff will always be better quality pixels than APS-c, given the same level of technology used on the sensor. The ff will perform better in low light, will have cleaner and higher images at higher ISO's, and cost more.
Title: Re: APS-C lens mm are correct
Post by: Don Haines on December 09, 2012, 09:38:44 AM
Don,

I agree with your summation but would change one word, "The difference in reach between ff and aps-c comes from the sensor,"

Should, for the sake of clarity, read "The difference in field of view between ff and aps-c comes from the sensor,"
Thanks! I edited my post to reflect your suggestion.
Title: Re: APS-C lens mm are correct
Post by: PackLight on December 09, 2012, 01:50:06 PM
And alot of people use alot of words irregardless of they're proper meaning.  That don't make them rite.  That be true to, even if we doesn't like it muchly.

("muchly", I found a new word to add to my vocabulary to frustarte my 5th grade english teacher  :D)

I have been thinking about this muchly and here is my thought;

Someone in reference to his photography asks about adding "perspective", changing the "perspective" or however they phrase the question.

His understanding may be in line with how you have defined it, or it may not.

The same person may have the understanding that "perspective" is the 3D illusion that some pictures have.
So do we tell the person they are incorrect when it comes to photography, do we tell this person that "the only thing that determines perspective is distance". I suppose we do, since that is the consensus of this thread.

I would hope if this person comes across an article that can take their photography to another level it doesn't hold that individual back from reading it because it is entitled "perspective" and the author has a different understanding of the definition. How can we have respect for this persons teachings if their understanding of the simple word "perspective" is different than ours. Just as in painting a photograph can have the illusion of depth by  altering colors, changing light intensity, shadows, changing the areas in focus  and altering the dimensional aspect and position and placement or location of objects. The difference is we have far less control on those aspects than someone painting. If someone describes these things as a way to control perspective in photography should we dismiss their teachings as they do not know what they are talking about?

I think explaining to someone that a 7D sensor does not have more "Reach" than a FF sensor, or that a EF-S lens at 100mm is not a 160mm in disguise, is a little more straight forward than describing "perspective". Again as you said "my opinion" thank ya muchly.  ;D


Title: Re: APS-C lens mm are correct
Post by: Don Haines on December 09, 2012, 03:10:08 PM
And alot of people use alot of words irregardless of they're proper meaning.  That don't make them rite.  That be true to, even if we doesn't like it muchly.

Neuro, you really made me smile here.....

"alot"

"they're"

regardless = without regard
irregardless - not a real word

"That don't make them rite"

"That be true to."

"muchly"

Either you are having way too much fun here, or you had more than one bottle of chocolate stout (possibly both).... Love it and keep up the good (bad?) work!
Title: Re: APS-C lens mm are correct
Post by: woollybear on December 09, 2012, 03:39:48 PM
Wow...I think I figured it out...

Put two photographers in a forum and you'll get three different opinions.
Title: Re: APS-C lens mm are correct
Post by: Chuck Alaimo on December 09, 2012, 10:49:52 PM
I guess my perspective on this is that someones point of view is distorted.  One thing about all of this is clear though --- neuro's shot of the beer - the file either lacks the resolution, or, the DOF of fields blurs it out too much, but I believe that from Neuro's perspective the chocolate stout is much nastier than whatever the one is behind it (IPA ?????).
Title: Re: APS-C lens mm are correct
Post by: Daniel Flather on December 10, 2012, 12:55:23 PM
Nice example privatebydesign. I presume the lady in the photo is trying to explain this over the phone to one of the doubters............. ;D

ROFLMFAO