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Author Topic: Sensor & Sensibility II  (Read 16666 times)
opgr
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« on: August 25, 2006, 08:48:22 AM »
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Like some of the others here, I had a hard time following the Sensor & Sensibility thread. And I don't consider myself technically challenged in any way, nor do I shy away from purely theoretical discussions.

However, I would like to redo a similar discussion, but in a more pragmatic approach. That is, instead of purely speculating about the advantages of larger pixel-bins, or whatever the preferred term is these days (minutes?), how about discussing the real world examples that are available to us, void of marketing speak...

DPReview has an interesting image test in the Canon 5D review at the bottom of this page and RAW example on the next page.

So the 5D obviously has large pixel-bins, if not the largest in the industry, and the 20D would be the perfect example of a camera that represents what most people here consider the best compromise between sensor-size, pixel-count, lens-performance, and printing resolution needs for most common situations.
(note that this is a premise you're obviously free to dispute if appropriate).

If I understand the various discussions properly, the question now becomes this:
Are the purported advantages of larger pixel-bins evident in the real-world performance and do they justify the expenses required?

Based on nothing but gut feeling I think that the 5D requires less processing than the 20D to yield the same performance figures which translates to more natural looking images at low iso, and a significant difference in processing latitude for high-iso images... ?
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Oscar Rysdyk
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Ray
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« Reply #1 on: August 25, 2006, 12:30:28 PM »
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I don't really have any doubt, Oscar, that the larger sensor with the larger pixel pitch will have certain advantages, either in terms of wider dynamic range, less noise, a shallower DoF capability, or higher resolution if it has more pixels as well as larger pixels, as the 5D has compared with the 20D.

Since I own both a 20D and 5D, I could be testing some of these issues myself. Perhaps I'll get around to it, one day.

However, I feel there's one important issue that is often ignored when comparing different format cameras, and that's the DoF equivalence at a required shutter speed. It's widely recognised that small format cameras, particularly P&S digicams, are of little use for creative photography employing shallow DoF. But the reverse is equally true. They are of great use for getting good DoF at wide apertures and fast shutter speeds.

Most comparisons between a 20D and 5D, I can almost guarantee, will be at the same aperture, same ISO and very similar shutter speeds, almost as though DoF is never a consideration. Since both DoF and shutter speed are usually amongst the most important considerations when composing a shot, it seems to me appropriate to make comparisons between the 5D at f11 and ISO 1600 and the 20D at f6.3 and ISO 600, for example (and of course same FoV). DoF and shutter speed will be the same, but the 20D might actually have less noise on the same size prints despite having smaller and fewer pixels. I'd be surprised if the 20D displayed more noise in these circumstances, but it's something I'll have to check for myself I guess.
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John Sheehy
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« Reply #2 on: August 25, 2006, 01:14:02 PM »
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If I understand the various discussions properly, the question now becomes this:
Are the purported advantages of larger pixel-bins evident in the real-world performance and do they justify the expenses required?
[a href=\"index.php?act=findpost&pid=74439\"][{POST_SNAPBACK}][/a]

The big pixels that capture more electrons per pixel will have higher signal-to-noise in the highlights, at the pixel level.  The blackframe noise, however, limits the dynamic range.  "Maximum signal divided by blacklevel noise" is the determiner of dynamic range.  "Maximum signal divided by the noise of *that* signal" is not DR, and the latter is what counting more photons does for you.

IOW, the bigger pixels mean a lot less noise in the highlights, and in the midtones, and even the brightest shadows (to a lesser extent), but do not help as much in the deeper shadows, and therefore with DR.
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opgr
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« Reply #3 on: August 25, 2006, 01:51:06 PM »
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IOW, the bigger pixels mean a lot less noise in the highlights, and in the midtones, and even the brightest shadows (to a lesser extent), but do not help as much in the deeper shadows, and therefore with DR.

What do you mean by "a lot less"? And how does that translate to real-world images?
Page 21 of the same review seems to suggest that the real world noise difference for gray is marginal, certainly not a lot less??

But suppose it's true, then it's obvious that the reduced noise advantage can only be harvested through more bits in the A/D conversion. But that's not the case. Both camera's use 12bits AFAIK.

What does seem to be the case is a difference in processing (noise reduction amongst others) required to generate the images. This translates to more natural looking images in the 5D, and better image performance at high iso.

Just saying that "bigger pixels = higher dynamic range and/or less noise" while all of the examples or technical graphs indicate otherwise, to me means we have to redefine how we judge the net effect of the advantages IF they truly exist...

Note that I'm not trying to attack the theory, I'm just trying to find out what improvements people actually SEE in an image from a large pixel-bin sensor vs a smaller pixel-bin sensor. How do the theoretical advantages actually translate into real-world images?
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Oscar Rysdyk
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opgr
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« Reply #4 on: August 25, 2006, 02:16:25 PM »
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However, I feel there's one important issue that is often ignored when comparing different format cameras, and that's the DoF equivalence at a required shutter speed. It's widely recognised that small format cameras, particularly P&S digicams, are of little use for creative photography employing shallow DoF. But the reverse is equally true. They are of great use for getting good DoF at wide apertures and fast shutter speeds.

Yes, but not if there is some theoretical limit to lens sharpness. And that is what we are alluding to in these discussions. Specifically now that we have a bunch of 10mpx APS-C cameras, and possibly a 1 series successor with anything between 22mp to 26mp.

The reason I like the comparison between a 5D sensor and a 20D sensor is that it is the closest thing to apples vs apples. Comparing a 5D sensor to a Sony chip has been less than useful in the past. Yes, the Sony chip is a lot more noisy, but that seems attributable to other aspects of design.
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Oscar Rysdyk
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bjanes
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« Reply #5 on: August 25, 2006, 02:20:49 PM »
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The big pixels that capture more electrons per pixel will have higher signal-to-noise in the highlights, at the pixel level.  The blackframe noise, however, limits the dynamic range.  "Maximum signal divided by blacklevel noise" is the determiner of dynamic range.  "Maximum signal divided by the noise of *that* signal" is not DR, and the latter is what counting more photons does for you.

IOW, the bigger pixels mean a lot less noise in the highlights, and in the midtones, and even the brightest shadows (to a lesser extent), but do not help as much in the deeper shadows, and therefore with DR.
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Jobn,

From your previous posts, I know that you are quite well versed in technical matters, but I must respectfully disagree with the above assertion. As you say, dynamic range is defined as full well electrons/read noise.

[a href=\"http://www.photomet.com/library_enc_dynamic.shtml]http://www.photomet.com/library_enc_dynamic.shtml[/url]

Read noise can be determined from very short exposures with the lens cap on as Roger Clark describes on his web site, but your use of blacklevel noise could cause confusion with dark current, which becomes bothersome with much longer exposures such as in astrophotography.

http://www.clarkvision.com/imagedetail/eva...-1d2/index.html

Other things being equal, a large sensor will have more dynamic range than a smaller one because the numerator of the above equation will be larger. The read noise of a large and small sensor may be similar, but the effect of n electrons of read noise will be smaller with the large pixel when the number of electrons of read noise is converted into a pixel data number, since the large pixel collects more electrons (i.e. the gain is larger with the large pixel). Roger discusses this matter further in this post:

http://www.clarkvision.com/imagedetail/doe...tter/index.html

With most digital cameras, highlight noise is dominated by shot noise and deep shadow noise by read noise, as you properly state. However, with large pixels, the effect of read noise on the data number will be less as explained above.
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opgr
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« Reply #6 on: August 25, 2006, 02:39:23 PM »
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With most digital cameras, highlight noise is dominated by shot noise and deep shadow noise by read noise, as you properly state. However, with large pixels, the effect of read noise on the data number will be less as explained above.
[a href=\"index.php?act=findpost&pid=74473\"][{POST_SNAPBACK}][/a]

Please don't get caught up in definitions or theory. (Perhaps the original thread is useful for that). I'm interested in the real-world, visible benefits. If you personally feel that some theory is the correct theory, do you then possibly have images to share that clearly show the corresponding benefits. Where are the higher dynamic range images? Where are the less noisy images?

I mean the significant images. The ones that justify the heated discussions. The ones that clearly show that 10 mpx is a step back if you happen to believe that. The ones that clearly show that paying a premium for FF, large pixel-bins has some substantial gain.

Or in case of P&S: if you take a 10mpx image and reduce the size to 6mpx, do those 6mpx then look a lot more pleasing due to anti-aliasing of the processing artifacts than a 6mpx image from a 6mpx sensor straight?
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Oscar Rysdyk
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bjanes
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« Reply #7 on: August 25, 2006, 03:46:55 PM »
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Please don't get caught up in definitions or theory. (Perhaps the original thread is useful for that). I'm interested in the real-world, visible benefits. If you personally feel that some theory is the correct theory, do you then possibly have images to share that clearly show the corresponding benefits. Where are the higher dynamic range images? Where are the less noisy images?

I mean the significant images. The ones that justify the heated discussions. The ones that clearly show that 10 mpx is a step back if you happen to believe that. The ones that clearly show that paying a premium for FF, large pixel-bins has some substantial gain.

Or in case of P&S: if you take a 10mpx image and reduce the size to 6mpx, do those 6mpx then look a lot more pleasing due to anti-aliasing of the processing artifacts than a 6mpx image from a 6mpx sensor straight?
[a href=\"index.php?act=findpost&pid=74477\"][{POST_SNAPBACK}][/a]

Opgr,

Do we need to do a drag race to show that a Porsche turbo can outrun a VW? The differences  between P&S and a large pixel camera such as the 5D are obvious, especially with higher ISO. Most noise measurements are handicapped by the in camera application of NR, which reduces detail along with noise. Sharpening also accentuates noise.

Meaningful tests require raw with no NR or sharpening, and many P&S do not even offer these options. Even so, just look at some of the images in DPReview between the 5D and the P&S cameras.

The Clark website compares P&S to the EOS 1D. The differences are dramatic. Why do photographic tests to show what should be obvious? I do not really see why Michael's essay has provoked so much controversy. What he said is generally accepted.
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opgr
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« Reply #8 on: August 25, 2006, 04:07:53 PM »
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Do we need to do a drag race to show that a Porsche turbo can outrun a VW? The differences  between P&S and a large pixel camera such as the 5D are obvious, especially with higher ISO.

I never referenced a comparison between DSLR and P&S.

The comparisons are between large pixel-bins a-la 5D vs smaller pixel-bins a-la 20D and whether the increase to 10mpx APS-C is sensible. The other comparison is between 6mpx and 10mpx P&S and whether that increase is sensible.

The former comparison also relates to a possible 1-series upgrade to 22+ mpx. The latter comparison may not be complete if we don't look at a reduced scale image to see if a 6mpx file from a 10mpx sensor is better than a 6mpx file from a 6mpx sensor straight...
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Oscar Rysdyk
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Ray
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« Reply #9 on: August 25, 2006, 08:04:22 PM »
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Yes, but not if there is some theoretical limit to lens sharpness. And that is what we are alluding to in these discussions. Specifically now that we have a bunch of 10mpx APS-C cameras, and possibly a 1 series successor with anything between 22mp to 26mp.

Oscar, with all due respect this is a red herring. Lens sharpness is always a concern whatever camera one is using and one certainly needs to know one's lenses if one is serious about these issues you've raised. For the comparison you've suggested, both cameras use the same lenses and most 35mm lenses have a range of a few stops where, for real world practical purposes, lens resolution is as close as matters. After all, we're talking about a 1 1/2 stop difference. Sometimes this difference will favour the 20D (eg f6.3 compared with f11, or f11 compared with f18) and sometimes it will favour the 5D (f2 compared with f3.5).

It should also be mentioned that system resolution does fall off to some degree at high ISOs. For example, if you want to see clear, undeniable differences between the 5D and 1Ds2, check out the dpreview images at ISO 1600 for these cameras. You'll find that the 1Ds2 is quite noticeably sharper (but also noisier) than the 5D at this ISO.

One should also bear in mind that a lens at (or close to) full aperture tends to lose performance around the edges, which doesn't concern the 20D. Of course, if you know a lens has noticeably worse resolution at a particular aperture, one would try to avoid using it for such comparisons. It would not be ideal to compare the 100-400 IS at f5.6 (and 400mm) using the 20D with the same lens at f9 using the 5D (at the same shutter speed but different ISO and different distance for same FoV). Such a comparison would tip the balance in favour of the 5D because we know this lens is noticeably soft at full aperture.

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The reason I like the comparison between a 5D sensor and a 20D sensor is that it is the closest thing to apples vs apples. Comparing a 5D sensor to a Sony chip has been less than useful in the past. Yes, the Sony chip is a lot more noisy, but that seems attributable to other aspects of design.

It is, but I believe that some of the qualitative differences you refer to are due to the fact that the 5D has over 50% more pixels and the individual pixels in both cameras appear to have similar noise characteristics.
« Last Edit: August 25, 2006, 08:06:04 PM by Ray » Logged
opgr
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« Reply #10 on: August 25, 2006, 11:34:16 PM »
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Oscar, with all due respect this is a red herring. Lens sharpness is always a concern whatever camera one is using and one certainly needs to know one's lenses if one is serious about these issues you've raised. For the comparison you've suggested, both cameras use the same lenses and most 35mm lenses have a range of a few stops where, for real world practical purposes, lens resolution is as close as matters. After all, we're talking about a 1 1/2 stop difference. Sometimes this difference will favour the 20D (eg f6.3 compared with f11, or f11 compared with f18) and sometimes it will favour the 5D (f2 compared with f3.5).

Ray,

It certainly isn't meant to be a red herring and I completely agree with your points and indicated differences between FF and APS-C. But I think that the whole sensibility issue revolves around the following question:

is it sensible to increase the megapixels in APS-C from 8 to 10?

people in the no-camp argue that 8 mpx;

1) is already at the limit of the resolving power of most lenses even at their optimal aperture,

2) is more than enough for most common printing needs,

3) has better image characteristics because of larger pixel-bins.

The same arguments are raised for the other two "formats", FF and P&S, but for different resolutions obviously. So we are comparing equal formats. The 5D vs 20D comparison rears its ugly head for argument 3 above, not argument 1 or FF vs APS-C differences.



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It is, but I believe that some of the qualitative differences you refer to are due to the fact that the 5D has over 50% more pixels and the individual pixels in both cameras appear to have similar noise characteristics.

But doesn't this completely negate the larger pixel-bin advantages?
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« Reply #11 on: August 26, 2006, 04:53:40 AM »
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is it sensible to increase the megapixels in APS-C from 8 to 10?

people in the no-camp argue that 8 mpx;

1) is already at the limit of the resolving power of most lenses even at their optimal aperture,

2) is more than enough for most common printing needs,

3) has better image characteristics because of larger pixel-bins.

[a href=\"index.php?act=findpost&pid=74513\"][{POST_SNAPBACK}][/a]

It would make sense to go from 8 to 10 Megapixels in line with advances in technology.

Without making this technical, the basis for my this statement is observation of improvements in the quality of images I could produce in moving from a 10D to a 1DII. Even though the 10D is 6Mpix and the 1DII is 8Mpix there is a noticeable improvement in the quality of pictures that can be produced, an increase in flexibility (or latitude) to adjust the image and a lowering of noise in the image. Most of this can be attributed to a general advance in technology rather than any particular sensor size, pixel density or pixel size.

Any comparison or generalisation made for today is unlikely to stand up in a year or two years as both camera and lens technology continue to improve.
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« Reply #12 on: August 26, 2006, 07:43:23 AM »
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Without making this technical, the basis for my this statement is observation of improvements in the quality of images I could produce in moving from a 10D to a 1DII. Even though the 10D is 6Mpix and the 1DII is 8Mpix there is a noticeable improvement in the quality of pictures that can be produced, an increase in flexibility (or latitude) to adjust the image and a lowering of noise in the image. Most of this can be attributed to a general advance in technology rather than any particular sensor size, pixel density or pixel size.[a href=\"index.php?act=findpost&pid=74522\"][{POST_SNAPBACK}][/a]

I would think that part of it would have to be the increase in pixel-to-pixel contrast with the coarser pixel-pitch, in the center of the images, as the farther-spaced pixels don't need to strain the MTF as much as the closer-spaced ones.
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« Reply #13 on: August 26, 2006, 07:56:37 AM »
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I would think that part of it would have to be the increase in pixel-to-pixel contrast with the coarser pixel-pitch, in the center of the images, as the farther-spaced pixels don't need to strain the MTF as much as the closer-spaced ones.
[a href=\"index.php?act=findpost&pid=74528\"][{POST_SNAPBACK}][/a]

Have you been on a special course to teach how to write bollocks dressed as techno-babble? As per your earlier comment on dynamic range which bjanes saved me the effort of commenting on, this is a complete load of drivel put in such a way as to sound intelligent.

The only thing being stained here is credibility.
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Ray
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« Reply #14 on: August 26, 2006, 08:02:45 AM »
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But doesn't this completely negate the larger pixel-bin advantages?
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Oscar,
It would if the 20D pixels really are of similar quality, dynamic range and S/N etc.

I suppose the way to test this would be to use the same lens on both cameras, at the same aperture and using the same ISO, but move back a certain distance with the 20D so that equal FoV crops from both images will contain the same number of pixels. Would you be able to calculate for me what that precise ratio of distance to target should be. I don't have a calculator at hand.  

I took a few shots today using my 25-105 with both cameras at different focal lengths, different apertures, different ISOs but same shutter speed and DoF. Didn't get things quite right though. As far as I can tell, there's no way of knowing the precise focal length untill the images are downloaded. I ended up comparing 75mm on the 5D with 50mm on the 20D, which is a crop factor of 1.5 and gives a slight advantage to the 20D. After an appropriate amount of sharpening, giving slightly more sharpening to the 20D image after interpolation, I find there's no noticeable differences in image quality in the central area of the image, at 67% enlargement on screen, which at my screen resolution of 1280x1024 would look like a 20x30" print, if my monitor was that big.

At 200% enlargement, representing a print size of around 5ftx7.5ft, the 5D image is slightly sharper, a bit like the difference between the 5D and 1Ds2.

The real surprise was the performance in the corners. I expected the crop factor of the 20D would deliver good results from corner to corner. Not so. The 5D image was very noticeably better in the corners; the difference between text being legible and illegible.

The 20D shot was at f6.3 and ISO 400; the 5D shot at f11 and ISO 1250. Same shutter speed for both images. Also surprisingly, the 5D did not show more noise in the shadows, despite the much higher ISO. I attribute this to the greater number of pixels of the 5D. The noise of the 20D pixels at ISO 400 is actually less, but not after the image has been interpolated to the same size as the 5D image.

I also checked resolution of the same target at f6.3 and f11 on the 5D at 75mm. Essentially there's resolution no difference at all between these two apertures, except in the corners again. It seems that f6.3 is too wide on this lens for good corner performance, even on the 20D.
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bjanes
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« Reply #15 on: August 26, 2006, 08:10:37 AM »
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It would make sense to go from 8 to 10 Megapixels in line with advances in technology.

Any comparison or generalisation made for today is unlikely to stand up in a year or two years as both camera and lens technology continue to improve.
[a href=\"index.php?act=findpost&pid=74522\"][{POST_SNAPBACK}][/a]

Unless the laws of physics change in the near future, one generalization that is likely to stand up is that large pixels will have less noise and small pixels will have better resolution. The tradeoff between these two factors depends on the situation. At base ISO, small pixels can produce excellent results as shown with the Nikon D2X, even with its inferior sensor technology. However, high ISO performance is poor.

For sports photography and photojournalism, where lighting is often poor, the large pixel is a distinct advantage and the Canon 1DMII would be a better choice. As Michael likes to say, "horses for courses".

Whatever improvements made with small pixel sensors can also be applied to those with larger pixels, and the relative merits of the different pixel size will remain unchanged.
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Ray
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« Reply #16 on: August 26, 2006, 08:18:36 AM »
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At base ISO, small pixels can produce excellent results as shown with the Nikon D2X, even with its inferior sensor technology. However, high ISO performance is poor.
[a href=\"index.php?act=findpost&pid=74534\"][{POST_SNAPBACK}][/a]

But once again, Bill, you don't alsways have the same need for the higher ISOs with a camera like the D2X. You can usually get the same results with a 1.5 stops bigger aperture and correspondingly lower ISO.
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« Reply #17 on: August 26, 2006, 08:28:58 AM »
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Unless the laws of physics change in the near future, one generalization that is likely to stand up is that large pixels will have less noise and small pixels will have better resolution. The tradeoff between these two factors depends on the situation. At base ISO, small pixels can produce excellent results as shown with the Nikon D2X, even with its inferior sensor technology. However, high ISO performance is poor.

[a href=\"index.php?act=findpost&pid=74534\"][{POST_SNAPBACK}][/a]

And also as the quality of lenses improves (i.e. better MTFs) then for the APS-C sized sensor a higher pixel pitch can be supported without running into limitations due to lens quality.

What you are fixating on is specifics of a particular argumentation and technical babble. The point I am making is that things will get better and we will see gradual increases in performance year on year. The fact that bigger pixels have less noise and smaller pixels have higher resolution is a load of bunk if we cannot SEE and increase in image quality. Oscar was asking if anyone can show or demonstrate real world improvements in image quality rather than discuss whether big or little pixels are THEORETICALLY better.

It's OK that people have amateur discussion on sensor performance, but they are just that, the musings of semi informed armchair enthusiasts. If anyone can back up the techno babble with some serious evidence then the arguments might be taken more seriously.
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Ray
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« Reply #18 on: August 26, 2006, 09:27:27 AM »
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If anyone can back up the techno babble with some serious evidence then the arguments might be taken more seriously.
[a href=\"index.php?act=findpost&pid=74537\"][{POST_SNAPBACK}][/a]

Here's my evidence to back up the techno babble, but using an ordinary lens unfortunately. At 100% enlargement, representing a print size larger than my Epson 7600 can handle, the superior resolving power of the 5D is beginning to show. One of the 100% crops below (maximum jpeg quality) is of a 20D image at 50mm, f6.3 and ISO 400. The other is the same crop of a 5D image at 75mm, f11 and ISO 1250.
 
I think it is very likely that a 400D would have narrowed this gap to irrelevancy at any enlargement, under these conditions of same DoF and shutter speed.

[attachment=919:attachment]           [attachment=920:attachment]
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« Reply #19 on: August 26, 2006, 09:46:56 AM »
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I suppose the way to test this would be to use the same lens on both cameras, at the same aperture and using the same ISO, but move back a certain distance with the 20D so that equal FoV crops from both images will contain the same number of pixels. Would you be able to calculate for me what that precise ratio of distance to target should be. I don't have a calculator at hand. 
Yes, you do.

Just go to Google, type your mathematical expression, and search.

If you're running Windows, there's been a calculator included with the system since version 1.0 in 1985.

If you're running MacOS X, there's a calculator widget available on F12, as well as the usual calculator tools on any sane Unix system.

You've simply got no excuse, Ray.  
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