March 03, 2015, 06:04:12 PM

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Messages - Lee Jay

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1
Lenses / Re: Canon ef-s 17-55mm 2.8 is usm GONE
« on: Today at 04:38:33 AM »
This is how I understand it (and feel free to correct me if I'm wrong):

  • For exposure, no difference between F2.8 on crop or on full frame.
  • For depth of field, there is a difference, but only if you maintain the same field of view.

The reason for the difference in depth of field is that to maintain the same field of view between crop and full frame, you have to change your distance from the subject, and that is what changes depth of field.

When you see someone say "F2.8 on a crop sensor is really F4.5 equivalent on full frame," they're talking about the depth of field for equivalent framing only, not exposure.

Teleconverters are another story (and might contribute to the confusion for some), because they DO affect exposure. I believe the reason for this is that it changes focal length (one of the inputs for the aperture value), which changes the ratio, affecting the light that can hit the sensor, and thus, exposure.

Any experts want to chime in to set me straight? :P
The EF-S 17-55/2.8 IS lens is f2.8, and there's no getting away from that. And it also has a focal length range of 17-55. And when shot on a crop body at ISO 5000, it is shot at ISO 5000.

While these cold hard facts are indisputable, it's only if you want to compare to different sensor formats that you have to start doing maths. If you don't, stop reading here.

While you can say it's the equivalent of a 27-88mm lens, due to the physical size of the entrance pupil (which can't alter at a given focal length and aperture setting), the equivalent aperture changes. (Take the lens set to 55mm, f2.8. The entrance pupil is 55mm/2.8, or 19.64mm. If you insist on calling 55mm 'equivalent' to 88mm, that fixed entrance pupil size means that at '88mm' the aperture ratio is 88/19.64, or 'f4.48'). Equivalent ISO can be calculated by multiplying by the sensor area ratio.

But, as I said, equivalence is only useful if you want to know how two different systems compare. If you only shoot one sensor size and/or have no interest in how your system is equivalent to anything else, it is irrelevant. As I said, f2.8 is f2.8. 55mm is 55mm. ISO 5000 is ISO 5000.
Thanks for great info.  DPReview is the source where I came across this equivalence thing. They mention it in every crop camera review. As soon as I realized this equivalence comes at the expense of either slower ss or higher ISO, It felt something wrong to me. I stopped thinking about  upgrading to FF.
If you use a crop camera, then you change to full frame, you WON'T have to use slower shutter speed or higher ISO. That's the whole point of the discussion above. An f/2.8 lens is an f/2.8 lens irrespective of the sensor size. The exposure doesn't change. Only the field of view and depth of field that the lens provides vary when you change sensor size.

And image noise.  So, DOF and noise change just like changing fstop and ISO on full frame.  That's why the discussion above from rs is absolutely correct.

3
Lenses / Re: Canon ef-s 17-55mm 2.8 is usm GONE
« on: March 02, 2015, 03:43:28 PM »
This lens needs to be replaced, and the new one needs to start at 15mm, not 17mm.  I can't believe how many low-end compacts start at 24mm-equivalent and that Canon only makes one crop-lens that does, the 15-85IS, and it's not even their top-of-the-line!

EF-s 15-60/2.8 IS with better build, please!

4
PowerShot / Re: New PowerShot G17 Coming in Spring [CR2]
« on: February 28, 2015, 07:28:34 PM »
I think that would make it not a G17, but a G?X something new like the G7X and G3X.  And this looks like it would be a bigger version of the G7X (faster and wider zoom range).  I suspect it would be a pretty big camera.

5
Lenses / Re: I'm Torn Between...
« on: February 27, 2015, 11:46:27 AM »
Thanks for the responses guys!! I may have to consider the 17-55 efs. But spending $800+ for a lens, I would prefer one that I can use on both full and crop cameras.

About the 17-55 efs, is it true that it have a problem pulling dust inside the lens? And the IS system on the lens; how is it? Is is smooth or jerky?

Do you need the f/2.8?  If not, the 15-85 is great.

The 17-55 dust problems are over blown, and the IS is quite good on both lenses.

You could buy a used 17-55 and sell it later, probably for about what you paid for it.

6
Lenses / Re: I'm Torn Between...
« on: February 27, 2015, 11:35:14 AM »
I recommend considering the EF-S 15-85 f/3.5-5.6 IS if you are shooting mostly in the daytime and don't need extreme selective focus.

That's a good point.  If you don't need the speed, it's an excellent lens.  I have one and love it.

7
Lenses / Re: I'm Torn Between...
« on: February 27, 2015, 11:12:42 AM »
Neither.  For crop, get the the EF-S 17-55 f2.8 IS.

This is the correct answer.  If you do sell your 7D Mark II for a full-frame camera, then sell the 17-55 too and get a 24-70 or 24-105 for the full-frame camera.  If you keep the 7D Mark II then decide if you want to keep or sell the 17-55.

8
Lenses / Re: Review: Canon EF 100-400mm f/4.5-5.6L IS II
« on: February 27, 2015, 09:28:19 AM »
I don't have one of the new ones yet, but I do have one of the old ones.

I think some people have missed the point of the new lens.

The old one has quite excellent basic optical performance - good resolution, low CA, etc.  However...it has three fundamental problems.

  • The output is inconsistent wide open with the IS engaged.  You could get sharp shots or soft shots depending on where the IS elements were at the time the shot was taken.  This issue largely goes away at f/8 instead of f/5.6.
  • The IS performance absolutely stinks.  One stop.  Combine that with the above need to stop down a stop and the IS is often (but not always) useless.
  • The lens has lousy handling.  I don't mean the push-pull, I mean the fact that the lock ring can twist the AF ring, and the lock ring is the natural place to put your hand, at least for me.  This means you're always screwing with the manual focus ring, usually unintentionally.

The new one appears to have solved all three of these problems, and slightly improved the already-great basic optical performance all at the same time.  That's an enormous step forward.

9
EOS Bodies / Re: Possible Canon EOS 5D Mark IV Spec Talk [CR2]
« on: February 25, 2015, 03:41:30 PM »
This is the way I see it.  And of course Lee Jay and PBD can add/correct me if needed.

To increase high ISO performance to me is to increase DR at high ISO/light-limited situations.  I need to increase FWC or max signal per pixel or QE, however you look at it.  You need to lower read noise.  HOW you do those two things I'm not really commenting about but if you can do that you can increase S/N at high ISO.  You already have less read noise with smaller pixels so why can't you increase the size or efficiency of the photodiode in the pixel?  I've been in discussions about smaller parts in and around the pixel to make way for larger photodiodes, for instance.  I can also see where the FWC could be more important than read noise and overcome the higher read noise by adding more signal because signal is additive whereas noise is added SQRT.  So in that case, larger pixels might still win.  This of course is all at equal sensor size and equal technology.


Increasing FWC (probably a poor term to use, max saturation is probably better) is definitely a way that you can improve DR at higher ISO. Reducing read noise can certainly help, but at higher ISO read noise is already quite low, 3e- or less these days usually, and it's tough to complain about that. The saturation point at higher ISOs is usually only a couple thousand e-, sometimes as little as a few hundred e-, so increasing the charge capacity of each pixel is probably the better way to improve SNR at high ISO.

You aren't thinking about this correctly.

At high ISO, FWC is limited artificially by all the gain.  The cells are fully capable of holding a lot more charge, and they do, but the A-D saturates because of all the analog gain.

Assuming you are at high ISO because you are light-limited (not a bad assumption, IMHO), then the ONLY way to increase DR is to reduce read noise (assuming Bayer dyes, same QE, etc.).

10
Lenses / Re: understanding "fastness"
« on: February 25, 2015, 02:36:51 PM »
If we take a lens like the 70-200/2.8, then you will see that as you change the focal length, the size of the entrance pupil will change in proportion to the the focal length, even though the front element stays the same.  This shows you that for a typical zoom design, it is the desired f-number at the longest focal length that determines the minimum size of the front element.

I've wondered about this before.  For the constant aperture zoom lenses, based on their physical design, could they also be made to be a variable aperture lens with a larger aperture on the short end of the range (or should I say, lower F number)?  For example, with the 70-200 f2.8, at 200mm the entrance pupil has to be ~71.4 mm.  If you took this same entrance pupil size with the focal length at 70mm, couldn't the lens max aperture be ~f1.0?  So does the lens maker limit how much the entrance pupil opens based on the focal length?  Or am I missing something (does it also have to do with the front element size?)?

So, the actual physical opening doesn't change.  What changes is the apparent size of that opening when seen from the front of the lens.  In essence, the front lens elements (those in front of the physical aperture) cause variable optical magnification of the aperture as focal length changes.

11
EOS Bodies - For Video / Re: A Suggestion on the EOS-1D C Replacement
« on: February 25, 2015, 05:20:11 AM »
Canon should just put these features in the 5D4. It would sell more 5D4s than splitting the line again for a camera I won't buy solely for 4K but also won't upgrade to a 5D4 because it lacks 4k.

From a marketing point of view, offering more product variants typically sells more units and brings greater sales revenue than just offering one. I am quite certain that Sony sells more A7 cameras by offering 4 variants for different primary uses compared to offering only one expensive "all in" camera.

Right.  That's why mp3 players + cell phones + small tablet computers + poor compact cameras combine to sell way more units than smart phones.

12
EOS Bodies / Re: Possible Canon EOS 5D Mark IV Spec Talk [CR2]
« on: February 24, 2015, 10:09:11 AM »
Every time there is a megapixel advance some people claim "no one needs that many pixels etc. etc. etc."; they said this at 3 mp, 5mp, 10mp etc.  More pixels is always better if you don't have to give up anything (not sure yet what the 5ds will require us yield).

ISO 6,400 limit with expansion to ISO 12,800 (same as the pocketable S120 with 1/1.7" sensor, by the way).
I suspect that the quality will not be the same  ::) ::) ::)

Right - which is why the 5DS should go much higher, not the same.

At that level though, can't you effectively increase the ISO in pp? There's not much difference (if any?) between doing it in camera at the boost settings or after the fact, is there? That's the impression I get from similar discussions I've seen.

The difference is speed, metering, and verification of correct settings.

I go though this on my 5D, which has a maximum ISO of 1600, 3200 base.  It's acceptable up to ISO 12,800 but using ISO 3200 and EC-2 is a pain, it's hard to use the image preview to see what you got, it doesn't work well at all in JPEG mode, and it's a hassle even in raw.

Just being able to set the exposure index you actually want to use would be a big help in practice.

13
EOS Bodies / Re: Possible Canon EOS 5D Mark IV Spec Talk [CR2]
« on: February 23, 2015, 10:49:30 PM »
Having higher pixel densities just reduces ISO performance.

No it doesn't.

Yes it does.

Someday someone needs to explain to me why this myth persists after a decade of things going the other way despite similar basic sensor performance (QE).

Because when your small pixel drowns in a sea of noise a large pixel will still be getting a signal. It is simple physics.

Way to advance an argument: "I'm right, you're wrong". I think both could do with an added [citation needed].

How about a test?

Pixels that would give you a 208MP full-frame sensor on the left, a 13MP full-frame sensor on the right.  Same ISO, same f-stop, same shutter speed, same lighting, same focal length, both processed from raw using the same settings on the same converter.



When you hit the bottom of the well you have hit the bottom of the well. No amount of averaging between wells is going to make it anything other than the bottom of the well. A larger pixel is a deeper well and will always provide a better signal than a smaller pixel.

Like I said, its physics.

Yeah, but you don't know any physics.

An ideal sensor would capture the location and wavelength of every incident photon individually.  Think of that as an infinite number of infinitely small pixels, most of which capture no photons at all.

14
EOS Bodies / Re: Possible Canon EOS 5D Mark IV Spec Talk [CR2]
« on: February 23, 2015, 10:46:48 PM »
Having higher pixel densities just reduces ISO performance.

No it doesn't.

Yes it does.

Someday someone needs to explain to me why this myth persists after a decade of things going the other way despite similar basic sensor performance (QE).

Because when your small pixel drowns in a sea of noise a large pixel will still be getting a signal. It is simple physics.

Way to advance an argument: "I'm right, you're wrong". I think both could do with an added [citation needed].

How about a test?

Pixels that would give you a 208MP full-frame sensor on the left, a 13MP full-frame sensor on the right.  Same ISO, same f-stop, same shutter speed, same lighting, same focal length, both processed from raw using the same settings on the same converter.



When you hit the bottom of the well you have hit the bottom of the well. No amount of averaging between wells is going to make it anything other than the bottom of the well. A larger pixel is a deeper well and will always provide a better signal than a smaller pixel.

Like I said, its physics.

Also, as I said, that 'comparison' is between two totally different sensor technologies, one is back-illuminated and the other isn't, so the two images mean nothing.

Nope.  Same basic sensor technology, same generation.

15
EOS Bodies / Re: Possible Canon EOS 5D Mark IV Spec Talk [CR2]
« on: February 23, 2015, 07:46:06 PM »
If you only talk about the same sized sensors then bigger pixels have the potential to be less noisy if built to the same tech, if for no other reason than less of the sensor area is taken up with the lithography.

Microlenses pretty much equalize that.

Smaller pixels tend to win whenever noise is shot-noise dominated.  Shot noise is pretty much pixel size invariant for the the same size final image, but noise reduction software beats out the block averaging done by larger pixels.  If you're read-noise dominated, bigger pixels can win, but smaller pixels tend to have less read noise too, partially or (in some cases) totally eliminating that advantage.  But you tend to be read-noise dominated only at very high ISOs in the 5 to 6 digit range or more.

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