April 17, 2014, 08:29:59 PM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - jrista

Pages: 1 ... 86 87 [88] 89 90 ... 215
1306
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 07, 2013, 12:23:51 AM »
Actually, DOF, by definition, is this:

Code: [Select]
DoF = (2 * N * c * f^2 * s^2) / (f^4 - (N^2 * c^2 * s^2))
The factor for CoC, circle of confusion, is c. It is effectively arbitrary. [...]


I suggest you read this first:

http://en.wikipedia.org/wiki/Depth_of_field

Do not miss this paragraph:

If the original image is enlarged to make the final image, the circle of confusion in the original image must be smaller than that in the final image by the ratio of enlargement. Cropping an image and enlarging to the same size final image as an uncropped image taken under the same conditions is equivalent to using a smaller format under the same conditions, so the cropped image has less DOF. (Stroebel 1976, 134, 136–37).

or this:

Note that the acceptable circle of confusion values for these formats are different because of the relative amount of magnification each format will need in order to be projected on a full-sized movie screen.


"to be projected on a full-sized movie screen"

That would be an enlargement by a factor of 20x, 30x, maybe more? Of course CoC is going to matter with such an enlargement, despite the fact that you sit back by 30 to 50 feet. I don't think most photographers enlarge much more than 2x, and the vast majority of photographers reduce their images (usually quite considerably) for publication online.

As for the quote from Strobel, in the 1970s, film was the primary means by which photography was done. CoC was usually considerably larger back then than it is today with pixels less than 10 microns in size. Particularly in the case of large format cameras. With such large CoC sizes, it was a more important factor, even for something as relatively simple as a 2-3x enlargement. More recent films manufactured with more modern technology have produced silver halide film grains on the order of a few microns in size (one film in particular that was used by Zeiss to test high grade fast optics apparently was capable of resolving 400lp/mm, more than any sensor that I know of as of yet), but generally speaking CoC sizes today are quite small when compared to the film of the 1970s (a CoC that is 2x the pixel pitch of the average pixel size today, which is around 5µm, would be 0.01mm...a CoC for medium and large format film from the '70s would be on the order of 0.2-0.3mm...a difference by a factor of over 20x). It takes a pretty significant enlargement (say projecting on a large movie screen) to make CoC a meaningful aspect of DoF for the majority of photographers today.

I would point out that I speak from experience. I print at 24x36, 30x40, and 32x48 on a fairly frequent basis. For those particular prints hanging on my walls, they are usually viewed standing back ten feet or so...no one has ever complained about my depth of field being too thin or too large, or that the inaccuracies in my 7D AF resulted in a horribly misfocused subject totally unworthy of such a large honor. ;)

Anyway...points have been made. The debate, once again, is going nowhere. I'm going to bed. It's up to you and Neuro now. :P

1307
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 11:53:11 PM »
Keep in mind the timeframe. Five years ago FF was much more expensive to manufacture than it is today. The fact that the 6D, still relatively new, sells for as little as $1700, is quite telling here.

It seems that Canon's fab procedure hasn't changed, at least from what we can tell.  Has the cost of silicon wafers come down that much?  Or could it be that Canon was reaping very high profit margins on the presumed high cost of a FF sensor, and now they've decided to push more units at a lower profit margin, as an alternative strategy to drive the bottom line?

Just sayin'.  Not that I'm cynical, or anything...   ::)

I do believe 300mm wafers have come down in cost. I remember them still having some challenges five to six years ago with defect rates on them (this is pretty agnostic of industry...not specific to sensor fabrication). It is obviously a less serious problem for tiny chips like GPUs and CPUs or other ICs. Growing the wafer crystals has become more refined over the years, in no small part to some of the advancements made while trying to perfect the process for growing 450mm wafer crystals (which, as far as I know, has still not been taken up by any IC manufacturing industry...there is apparently a very high initial cost to jumping that has to be recouped, something no manufacturer seems willing to deal with as of yet).

As far as I know, it's not that actual growing of the Silicon ingots to 300mm (or 450mm for that matter) that is the yield/cost issue. Getting very high quality and uniform ingots has always been extremely important to high-voltage devices (think kilo-Volts), because spikes in dopant concentration can result in avalanche-type catastrophic breakdowns (leading to the magic blue smoke leaving the devices in spectacular ways).

It's the yield of the manufacturing processes for everything you on the base wafer that matter (diffusion, implants, etching, photo lithography, metallization etc).

The problem for the jump to 450mm wafers is that you need the entire infrastructure of a fab to be in place: steppers, aligners, photo lithography, and so on. It's so expensive to develop, that basically the entire IC industry needs to coordinate around it; it's not enough that Intel or TSMC (or both) says "hey, we want to do 450mm now" and presto! they have it.

Agreed on the last part...it is an industry-wide resistance to migrating to larger wafers. New fabs are built at an increasing rate, however, as more IC devices are used in an ever increasing array of applications. I figure someone would have put the money into building a new fab capable of 450mm by now...

I did read an article some time back, maybe seven or eight years ago now, that indicated that growing the crystal did not always produce perfect, uniform growth, and that further refinements of the process could improve quality and render an increase in usable 300mm wafers and fewer defects per wafer. I don't remember if it was online or in a magazine.

1308
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 11:42:14 PM »
I probably shouldn't even try, because it seems that you won't be convinced, but why not one last go?   ;)

If you do not change FL and distance, and keep it at f/2.8, DOF changes; cropping makes in shallower. AF errors are magnified.
Sorry, no.  Cropping doesn't change DoF.  Cropping then magnifying does change DoF,

Of course, you magnify when you crop (by crop, I mean use a smaller sensor). Do you use a smaller screen do display your smaller sensor photos? DOF by definition is relative to a reference print size. That size is kept the same regardless of the sensor. Do I need to spell out everything?

Actually, DOF, by definition, is this:

Code: [Select]
DoF = (2 * N * c * f^2 * s^2) / (f^4 - (N^2 * c^2 * s^2))
The factor for CoC, circle of confusion, is c. It is effectively arbitrary. One does not necessarily know what the final output size of their photo will be in the end, or even if there may be multiple output sizes. If one wishes to be as concrete as possible, the CoC is physically limited by pixel size. To be "safe" when using a bayer type sensor, one should usually use a CoC that is at least twice the pixel pitch to account for the uneven sampling. Because of the even sparser nature of red and blue pixels relative to green, and due to the fact that an AA filter is usually used, it is better to use a CoC roughly three times the pixel pitch. That would be the only truly concrete definition of CoC for any given sensor.

Assuming one uses the pixel pitch x3 for CoC, then that greatly simplifies the initial argument, and do away with the notion of a reference print size. One could assume that the pixel pitch for a FF sensor and an APS-C sensor are identical. If that is the case, then one could photograph the same subject with the same lens at the same distance with both sensors, crop the FF to the same image dimensions as the APS-C, and the depth of field will be 100% identical in every respect, regardless of what size the images are scaled to. Therefor, depth of field has nothing to do with crop factor or field of view.

Nor, for that matter, does it really have anything to do with a reference print size. I would also offer the argument that even in print, as print size increases, so too does the most comfortable viewing distance. If you have the luxury of 80mp of MFD goodness, you might be able to print a highly detailed photo in an immense 40x60" size at 360ppi, drawing your viewers to within a few feet to examine all the detail. It you are incredibly meticulous, careful scaling might eek out enough detail do do something similar from something like the D800 or a hypothetical 40-50mp Canon FF. Generally speaking, as print size increases ppi drops, and so too does the viewers desire to stand back farther and farther to take the whole thing in. As visual acuity is also a function of distance, CoC could, for all intents and purposes, be a constant...and therefor a non-factor when one needs to determine their depth of field. You can pick whatever CoC your "comfortable" with, use that same value every time you compute DoF...at which point the formula above proves the point once and for all.

I guess therefor that one could then state that DoF is, by definition, purely a function of the lens and relative to viewing distance of the final output, at the time the photo is taken. ;)

1309
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 10:24:43 PM »
I probably shouldn't even try, because it seems that you won't be convinced, but why not one last go?   ;)




 ;) ;D

1310
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 07:40:54 PM »
Sorry, but that's incorrect.  The precision of the AF points at a given aperture isn't specified in terms of DoF. Well, ok, maybe it is...but in that case, you keep using the letter F in the abbreviation, and I do not think it means what you think it means. 

The AF sensor precision spec is 'within one depth of focus' for a standard precision point, and 'within 1/3 the depth of focus' for high precision (f/2.8, usually) points.  Depth of focus is in 'image space' and is measured in micrometer distances at the AF (and/or image) sensor. It is related to, but distinct from, depth of field, which is measured in larger distances in 'object space'. 

I believe I was correct. While DOF and depth of focus are different, 1 D-O-focus is defined as the distance at which you get an image blurred by "1 DOF" (with a fixed COC), so 1/3 D-O-focus corresponds approximately to 1/3 DOF blur.

Another way to look at this: an f/2.8 eq. lens on crop is a f/1.75 one. The crop AF sensor cannot see rays coming from the periphery of such a lens. It has to somehow compensate this by judging the phase difference of f/4.5 (eq.) rays. Of course, those are rays of a shorter FL, so this is not exactly a proof without knowing how the AF system exactly works.

Hmm, I know that the image sensor cannot see from the periphery of any EF lens. I was not aware that the AF sensor was also limited in the same way. The point spread is certainly smaller than on a FF sensor (but I always figured that was an advantage as it doesn't have to deal with vignetting). I do not believe that actually limits the sensor's periphery vision. Do you have some kind of reference for this?

1311
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 07:29:51 PM »
The only difference then would simply be that the 7D frame is cropped, resolved by a higher density sensor, and thus appears to be zoomed more.

And that decreases the DOF and magnifies the AF errors (just another way to say the same thing).

Cropping does not change the depth of field. Depth of field is a function of the lens...the size of the square inside the imaging circle does not have any impact on the depth of field whatsoever. Circle of Confusion (which CAN be, but is not necessarily, a function of the pixel density, plays a role...but as I stated before, that is for all intents and purposes an arbitrary value. You can pick a number, so long as it is not smaller than the pixel pitch times two at the smallest, and use it for both APS-C and FF):

Code: [Select]
DoF = (2 * N * c * f^2 * s^2) / (f^4 - (N^2 * c^2 * s^2))
Where:

N = F#
f = focal length of LENS (crop factor need not apply)
s = distance to subject
c = circle of confusion

Lets say we are scaling for web. CoC is a non factor...we can pick anything, lets say 30 microns (0.03mm, probably far to small, but it really doesn't matter). If we run that for a 600mm lens at f/4 with a subject at 40 feet, we get a DoF of 4" (four inches), or about a third of a foot. With a CoC of 20 microns, we get a DoF of about 2.6". If we pick a CoC that is some happy medium between three times the pixel pitch of the 5D III and 7D cameras (to allow for AA filters and the nature of a bayer design), we get 16 microns. Our DoF is still about 2". If we are scaling down by 2x or more, these differences are moot...the effective CoC is FAR larger than any of these options.

We could even print somewhere near the native size of a 24mp APS-C or a cropped and scaled 23mp FF, something in the range of 16x24. There is a CoC difference, but from a practical standpoint, it doesn't produce a meaningful visual change in such a print. If we scaled up by 2x or so, then we'll probably start seeing a difference in DoF just by observing the print. Is it a meaningful difference? I guess it depends...if your printing at 150ppi on 30x40, its not really going to be the most significant factor affecting IQ or the sharpness of your subject, and your viewers will usually likely be standing back far enough to compensate for the difference. It may be an issue in this case, but so long as the important parts of your subject are in focus (which in my case is usually a birds head and maybe the side of its body, not even necessarily the whole body...anything on the back side of a bird can be entirely out of focus since it isn't visible...and a bird angled towards the lens can have blurry tail feathers and it doesn't really matter so long as the head and eyes are in clear focus), again CoC isn't really going to be the most important of a factor in determining the depth of field.

The real (actual) focal length of the lens, distance to subject, and selected aperture are the things that truly matter when it comes to DoF. Crop factor should NOT be factored into the focal length to produce an effective focal length first. Pixel pitch differences may need to be factored in if one intends to enlarge and print large, especially if they are printing at a higher resolution than 150ppi on anything other than canvas. Pixel pitch differences are effectively a non-issue if one intends to scale down and publish to the web.

In the event that you get closer with a 5D III+600/4 setup and frame the subject identically, then there would indeed be a fairly significant change in DoF. But that would be because the distance to subject shrunk. All things being equal, I would prefer to have the thinner DoF (and getting closer with a 5D III has the potential to pack even more pixels onto the subject than even a 7D can), even when photographing birds...but it is not always a possibility.

1312
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 04:42:45 PM »
I'm curious about the f/4.5 bit...how exactly does that work? Is that only for the outer points? (I believe the center AF point is still f/2.8 compatible like with most Canon AF systems.)

It works at f/2.8, of course, but that is equivalent to f/4.5, even though some people do not want to hear about that. Assuming that it has the same precision: 1/3 of DOF or so, it is 1/3 (or whatever) of the f/4.5 eq. DOF. It is like shooting with FF at f/4.5, with 1/3 DOF precision. Well, that is 1/3 of the DOF at f/4.5 Even if f/4.5 is all you need as DOF, your precision is lower. Some empirical evidence on that can be found on the FoCal site.

Oh, your talking about DOF. Yeah, entirely agree, since you are cropping the field of view you may have to get farther back, so DOF would then increase. But that assumes you have to move back to frame your subject. Assuming you use a camera like the 7D II for its reach benefit, then its DOF would be the same as a FF with the same lens from the same distance. The only difference then would simply be that the 7D frame is cropped, resolved by a higher density sensor, and thus appears to be zoomed more. (There are CoC caveats, but that depends on output size, and there is no way to really nail that down....you could enlarge, reduce, crop, whatever.)

1313
Animal Kingdom / Re: Show your Bird Portraits
« on: August 06, 2013, 04:13:19 PM »
Jrista,

Tried the Kenko 1.4x(DG Pro 300 "red dot") very briefly on the 500mm when I had it - whilst I didn't try any tracking shots, the static images were super sharp. At 700mm I couldn't find fault in the test shots I took. I know the Canon mk3 TCs should be better but assuming I buy the 500mm, the Kenko would do for a while if I needed more reach than 500mm.

Regards,

Guy.

I guess it depends on how much you are cropping. Once I started using the 600 on my 7D, especially with the 1.4x TCs, birds got really huge in the frame. Sometimes I have to move back with some shorebirds, waders, and waterfowl. With the Kenko, you notice the IQ falloff as you approach the corners. Even midframe, there is some noticeable softening, and in the edges and corners, definite CA. I don't see nearly as much of that with the EF 1.4x TC III. In the deep corners you see some CA, but for the most part, it seems to have a flatter field, and IQ overall is much nicer. AF performance is good...not all that much faster (Canon really seems to slow it down on the 7D), but definitely more consistent...the drive just seems to work better.

If birds are still only filling the center of the frame, then the IQ difference between the Kenko and Canon 1.4x TCs isn't really noticeable outside of some extreme pixel peeping.

1314
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 04:09:50 PM »
Sure, of course the converse is true (I never stated otherwise). My point is that the fact that the 6D has a larger sensor than the 7D II will likely have does not intrinsically put it at a higher or lower ranking on any hypothetical scale.

So we actually agree. I said next several times, not above or below.

Sorry, guess I missed that (or maybe mistakenly attributed someone elses comment to you...apologies.) Glad we agree. :)

Quote
For those who need an APS-C sensor in a camera with high FPS and excellent AF, the 7D II would, for them, be the better choice than the 6D for sure, and in some cases even better than the 5D III, and certainly a far more accessible option than the 1D X (even at a price point of $2500!)

Not so sure about the AF. The 7D has more advanced but less accurate AF (aside from tracking and advanced capabilities) than the 5D2. Format differences play role here, too. In equivalent terms, the 7D's AF is f/4.5 (!).

I agree that the 7D's AF is advanced but inconsistent (even when tracking, even on slow mode, it still tends to jump around far too much). Its probably my biggest complaint with it, and why I sincerely hope the 7D II gets something much more like the 61pt AF of the 5D III/1D X. Accuracy, precision, and consistency would make the 7D II a much more viable "mini 1D X".

I'm curious about the f/4.5 bit...how exactly does that work? Is that only for the outer points? (I believe the center AF point is still f/2.8 compatible like with most Canon AF systems.)

1315
Animal Kingdom / Re: Show your Bird Portraits
« on: August 06, 2013, 02:33:00 PM »
From a falconry display.

5D3 300mm f2.8 IS mk1 plus 1.4x Kenko TC.


The second one is awesome.

Thanks Click.

The owl was only about 9 inches in height (coulda just stuck it in my pocket!) and was used for a quick display for small kids - flying from its perch onto the kids' outstretched arms. I took tons of shots but only got a couple that were sharp. I think the Kenko TC slowed down the focus speed/reaction time of the 5D3 and 300mm.

I was using the combo to help decide if I should get a 500mm mk2. Overall the 300mm on its own is terrific but with the TC I wasn't completely thrilled with the results from the afternoon; some good, many bad. I hired the 500mm for an airshow a couple of weeks back and was amazed at the quality. Clearly you wouldn't use the 500mm for falconry due to the proximity of the action but I wanted to see how snappy the 300+1.4x combo would be. Might be acceptable to some, not me. Sigh, that'll be more money on this hobby.... :D

The Kenko TC, while a good price, is definitely a drag on AF performance. I own the GDX 300, and enjoyed it before, but since purchasing the 600/4 II, it just doesn't perform as well as the EF 1.4x TC III. I use the latter exclusively now...just not worth the performance hassles and AF perf loss of the Kenko.

1316
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 01:26:57 PM »
As has been stated frequently before on these forums, especially by Neuro, the sensor is often one of the least important features for many types of photography. 

I am not sure what Neuro actually said, but the fact is that the sensor size (not necessarily mp count or DR, or noise) is one of the most important factors in many types of photography, excluding macro and telephoto. To be more precise, it is one of the most important factors when you care, but then the same applies to lens choices, smartphone cameras vs. more serious ones, MF/LF vs. 35mm, etc.

Sure, of course the converse is true (I never stated otherwise). My point is that the fact that the 6D has a larger sensor than the 7D II will likely have does not intrinsically put it at a higher or lower ranking on any hypothetical scale. They are different tools for different jobs. For those who need a FF sensor because it IS the most important factor, the 6D and 5D III offer excellent options. For those who need an APS-C sensor in a camera with high FPS and excellent AF, the 7D II would, for them, be the better choice than the 6D for sure, and in some cases even better than the 5D III, and certainly a far more accessible option than the 1D X (even at a price point of $2500!)

I'm just trying to debunk the notion that the 6D, simply because of its model number and sensor size, therefor must be better or higher ranked or more professional than the 7D line. I would put the two at an equal level or tier of professional grade DSLR equipment, designed for different use cases and photography types, with feature sets to match.

1317
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 12:57:45 PM »
Keep in mind the timeframe. Five years ago FF was much more expensive to manufacture than it is today. The fact that the 6D, still relatively new, sells for as little as $1700, is quite telling here.

It seems that Canon's fab procedure hasn't changed, at least from what we can tell.  Has the cost of silicon wafers come down that much?  Or could it be that Canon was reaping very high profit margins on the presumed high cost of a FF sensor, and now they've decided to push more units at a lower profit margin, as an alternative strategy to drive the bottom line?

Just sayin'.  Not that I'm cynical, or anything...   ::)

I do believe 300mm wafers have come down in cost. I remember them still having some challenges five to six years ago with defect rates on them (this is pretty agnostic of industry...not specific to sensor fabrication). It is obviously a less serious problem for tiny chips like GPUs and CPUs or other ICs. Growing the wafer crystals has become more refined over the years, in no small part to some of the advancements made while trying to perfect the process for growing 450mm wafer crystals (which, as far as I know, has still not been taken up by any IC manufacturing industry...there is apparently a very high initial cost to jumping that has to be recouped, something no manufacturer seems willing to deal with as of yet).

As for Canon's real margins, honestly can't say there. I suspect they incurred the same kinds of high costs initially to move to a 300mm wafer, just like everyone else...however once those costs were recouped, it is entirely likely they were selling the 5D II at significant margins. That wouldn't be mutually exclusive with any drop in price for fabricating on 300mm wafers, however. Given that it is Canon, I'm sure they raked in the dough for as long as they could. ;P

1318
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 12:49:32 PM »
Keep in mind the timeframe. Five years ago FF was much more expensive to manufacture than it is today. The fact that the 6D, still relatively new, sells for as little as $1700, is quite telling here.

Today's BH prices:

60D: $600 (-1)
6D: $2,000 (-1)

More than three times more expensive.

Years ago, you could by a Rebel only for $600, and I am not even adjusting for inflation. Going back further, I think I paid $800 for my 350D (with the crappy kit lens), several years after it was released.

I am not sure how that is relevant to the part of my answer you quoted. The 60D is an APS-C part, and was never part of either Neuros post I replied to nor my post.

I was explicitly stating that five years ago, manufacturing a FF sensor was much more expensive than it is today, while manufacturing an APS-C sensor hasn't really gotten much cheaper. The drop in cost for FF relative to only a slightly lower cost for APS-C, as well as the fact that you can easily pick up a 6D for around $1700 on sale, would indicate that sensor size is not the primary price driver for these cameras in this bracket these days. A  $2000 list price 6D is therefor not necessarily better in any significant way than a $2000 7D II. On the contrary, the 7D II could hypothetically offer far more features, including more professional grade features, than the 6D.

As has been stated frequently before on these forums, especially by Neuro, the sensor is often one of the least important features for many types of photography. As such, why would it be the sole thing that determines how "professional" a professional grade camera is?

1319
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 06, 2013, 09:50:24 AM »
It would be missing more than half of the sensor.
and that's the only thing 6D offers. better IQ and ISO. 7D(2) on the other hand:
- FPS
- AF speed, spread and points
- CF
- buffer
- 100% VF and 1x magnification
- more custom functions
- better weather sealing and durability
- (Dual, +?) Digic 6 processor for the 7D2
- the tag "TOP APS-C"

and the list goes on. i completely see how its priced above 6D, even though i would rather see it not get above it. but in 1 year time, when 7D2 is supposedly released, 6D's price will plummet due to its age and.. you know the rest.

Interestingly, except for CF as a difference, your list sounds a just like a comparison between the 5DII and 7D.  Which of those was more expensive?

Keep in mind the timeframe. Five years ago FF was much more expensive to manufacture than it is today. The fact that the 6D, still relatively new, sells for as little as $1700, is quite telling here. I am not sure that a comparison of the 5D II and 7D from four to five years ago is good enough to predict the future in the case of the 6D/7DII of next year.

The two cameras are different, for sure...but that does not mean they don't both qualify for the same level of "pro" gear. Functionally, the 7D II (at least as the rumors stand now) sounds like a much more professional, higher grade part than the 6D...regardless of what the numbers may seem to indicate.

1320
EOS Bodies / Re: EOS 7D Mark II Information [CR2]
« on: August 05, 2013, 10:53:05 PM »
Prototypes for a 7D Mark II now exist over a year, but if I look at the 70D and 6D price I think that there is no space for an 7D Mark II between the mentioned cameras.

But why can't a 7D2 with faster burst rate and superior focus system sit ABOVE the 6D?

It would be missing more than half of the sensor.

But the sensor isn't everything..... For the sake of argument, what if you made the 7D2 with the 70D sensor, yet with the features and autofocus capabilities of the 1DX? Where would that sit?

Perhaps the 7D2 will come out with a new mode, one that will make it indispensable for people taking pictures for facebook?

Haha, love the cat face icon. :D

Pages: 1 ... 86 87 [88] 89 90 ... 215