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Author Topic: Canon 50D @ 15MP  (Read 114105 times)

BruceHouston

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« Reply #60 on: August 26, 2008, 11:36:43 pm »

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I'm afraid you are reading too much into a propaganda communiqué. Canon and Mr. Westfall are extremely selective with any technical information. (Example: they were not prepared to reveal the way HTP is working - like it would be some information worthy for keeping secret.)

I suggest to use some reasoning. For example: by mounting a large ancilliary lens on the camera's lens' front, one could increase the amount of captured light. This would lead to an increase of the nominal ISO. Would this increase the DR as well?

Of course, the larger/more effective microlenses increase the amount of captured light. This leads to less noise compared to a shot with teh same exposure but less effective microlenses. However, again, this leads to earlier saturation as well.
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I give up.  
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Ray

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« Reply #61 on: August 26, 2008, 11:52:22 pm »

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Lens resolution has to do a lot with pixel resolution (not with pixel count), namely if the lens does not resolve enough, then the high pixel resolution is useless.

Lens resolution cannot be measured by recording images on a digital sensor or film, hence the limitation of the sort of test results one finds at Photozone where one is correctly advised that one should not compare different systems in order to understand the quality of the lens.

Traditionally, lens resolution used to be measured by projecting an image of a line chart onto a very fine screen and then employing someone to count the visible lines using a microscope. As soon as you attempt to record the image (whether the image is of a line chart or any real-world scene) the image is degraded by the recording medium, whether that's film or sensor.

Recorded images provide you with 'system' resolution. It is of course possible to make certain deductions about the lens, from such recorded images, if you know the qualities of the recording medium.

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I find these comparisons irrelevant and your underlying principles misguided, just like your mixing up the circle of confusion with sensor size.

The underlying principle is not misguided. It's simply an underlying principle. It's application may be misguided. However, as I've already mentioned, I have observed in my own shooting a marginal increase in detail with the 20D at F22 compared with the same scene taken with the 5D with the same lens at the same aperture (cropped to the 20D FoV).

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However, I do not intend to convince you from the correctness of my viewpoint.

Tony Beach has already provided some photographic examples demonstrating that your hypothesis is not correct.
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Ray

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« Reply #62 on: August 26, 2008, 11:56:05 pm »

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No, but resolution won't be any better when you hit the diffraction wall.  Lots of consumers are going to be scratching their heads when they don't see any improvement going from a 40D to a 50D shooting at f/11.
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Tony,
There's no diffraction wall. It's more like a forest that gets denser and thicker the further you penetrate (the more you stop down).

There's a progression from apertures at which non-diffraction aberrations predominate, to apertures at which diffraction effects predominate.

In order to very precisely realise the full resolution potential of any lens at any aperture, you would ideally need the perfect sensor with infinite resolution at 100% MTF. Of course, we don't need (and can never get) anywhere near such precision as photographers, but any improvement in either lens or sensor is welcome.
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Panopeeper

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« Reply #63 on: August 27, 2008, 12:13:03 am »

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My experience with previous DSLR (starting with the D2x) clear shows that the sensor is not linear in the .1 brighest stop where it matter most.
I wonder how you came to this result. I have (and have analyzed) D2X images as well, with much clipping, and never seen anything like that.

There exists a special kind of non-linearity: many sensors of Nikon, Canon as well, exhibit a strange behaviour, and this depends not only on the model but on the individual copies as well: different pixels have different saturation points. I demonstrated this in the Rawnalyze handbook, see http://www.cryptobola.com/PhotoBola/RawnalyzeGuideAll.htm, Exposure Display; the example is from a D200.

This range, in the example from 3995 to 4025 is practically useless. Nevertheless, the individual pixels still yield linear values.
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Gabor

AJSJones

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« Reply #64 on: August 27, 2008, 01:00:32 am »

Check out emil's explanation in the second post of this thread  I found it helpful
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NikosR

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« Reply #65 on: August 27, 2008, 02:15:22 am »

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http://www.cambridgeincolour.com/tutorials...photography.htm

Read and learn, and then you can do what Thom Hogan and others (including myself) have done, and do comparisons between various pixel pitch DSLRs at various apertures and see for yourself.



As you can see, a 12 MP DSLR was reduced to no better than a 6 MP DSLR at f/16; I'm not sure why the 12 MP DSLR pulls ahead at f/22 (probably a smoother shutter), but since they both look like crap I hardly care.

As recently as today, Thom Hogan has posted at DPR on this very topic:  http://forums.dpreview.com/forums/read.asp...essage=29080207
You must have done direct comparisons to make such a bold statement.  Why do I think you are blowing smoke?

The issue will be at f/11, and I will bet you that at f/8 you will see an improvement but at f/11 the 40D will pull even with the 50D because the 50D will have become diffraction limited at f/8.
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Tony, the point where diffraction effect is noticeable is a function of both the lens and the pixel pitch. A lens 'causes' diffraction, the sensor, depending on its pixel pitch, is able to record this or not. Diffraction limits the resolution of any lens AT THE POINT where other optical aberrations do not limit resolution much more than diffraction does.

What this all amounts to is that, yes, a smaller pitched sensor will show the effects of diffraction earlier BUT the diffraction effect itself will depend on the lens used. So at what point diffraction effects will equalize the system resolution between the 40D and the 50D will depend on the lens.

In practice though and with average lenses that are not diffraction limited until they reach quite a small aperture, the effect will be as you describe. That will not be true though with very high quality lenses which are diffraction limited at very large apertures. Which, I guess, is a very convoluted way of saying that the higher the pixel pitch the better lenses must be used to show off the MP advantage.

All this is well known to us Nikon users who have had the chance of using the D2x.
« Last Edit: August 27, 2008, 02:19:21 am by NikosR »
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Nikos

Tony Beach

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« Reply #66 on: August 27, 2008, 02:20:34 am »

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Tony,
There's no diffraction wall.[a href=\"index.php?act=findpost&pid=217489\"][{POST_SNAPBACK}][/a]

I wonder if you read the links provided in post #39.  Anyway, whether you did or not, I don't really care because I know what I have seen with my own eyes and I provided visual proof in that post that confirms the theory and the observations of Thom Hogan and others.
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Nick Rains

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« Reply #67 on: August 27, 2008, 02:55:53 am »

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I wonder if you read the links provided in post #39.  Anyway, whether you did or not, I don't really care because I know what I have seen with my own eyes and I provided visual proof in that post that confirms the theory and the observations of Thom Hogan and others.
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I think what Ray meant is that the effect is not some absolute limit like a cliff but more of a slope. Your post with the text image clearly shows a worsening of the sharpness just as the theory predicts, but not a 'wall' past which everything is immediately dreadful.

I'm pretty sure Ray was merely pointing this out rather than disputing the results, which, in the case of your post, show up quite clearly.

The term 'diffraction limit' does imply some sort of end point whereas in reality it is merely a gradual appearance of the effect to the point where it is subjectively unacceptable. 'Diffraction effect threshold' might be a clearer term.

In my view it's like DoF; it's not a clear cut range, just a gradual lessening of absolute sharpness to the point where it becomes visible.
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Nick Rains
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Tony Beach

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« Reply #68 on: August 27, 2008, 03:21:25 am »

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In practice though and with average lenses that are not diffraction limited until they reach quite a small aperture, the effect will be as you describe. That will not be true though with very high quality lenses which are diffraction limited at very large apertures. Which, I guess, is a very convoluted way of saying that the higher the pixel pitch the better lenses must be used to show off the MP advantage.

All this is well known to us Nikon users who have had the chance of using the D2x.
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What lens would you recommend I use?

Here's 100% crops from my Nikkor 14-24/2.8 at 19mm taken under rigorously controlled conditions (studio lights, solid tripod, MLU, shot in RAW and processed identically):



I bet you can tell which side was f/11 and which side was f/16.
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Tony Beach

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« Reply #69 on: August 27, 2008, 03:31:08 am »

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In my view it's like DoF; it's not a clear cut range, just a gradual lessening of absolute sharpness to the point where it becomes visible.
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It is my contention that by the time you reach f/11, there will be no difference between a 40D file and a 50D file.  I could be wrong primarily due to AA filter strength, but I'm convinced that the 50D is going to start being diffraction impaired at about f/8.  Losing a third or even half your resolution over a stop will be significant, whether you would call that a "wall" or "gradual" is a matter of semantics.  Anyway, I like your term "Diffraction effect threshold".
« Last Edit: August 27, 2008, 03:32:55 am by Tony Beach »
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NikosR

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« Reply #70 on: August 27, 2008, 04:11:51 am »

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What lens would you recommend I use?

Here's 100% crops from my Nikkor 14-24/2.8 at 19mm taken under rigorously controlled conditions (studio lights, solid tripod, MLU, shot in RAW and processed identically):



I bet you can tell which side was f/11 and which side was f/16.
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This has no relevance to what I was talking about. Nobody is contesting the fact that diffraction effects are noticeable at very small apertures. The issue is when this has an equalizing effect between different pitched sensors.

BTW A top quality long lens like the 300 2.8  is the one to use for such tests as these tend to be difraction limited at wide apertures i.e. no significant resolution improvement is evident by closing down.
« Last Edit: August 27, 2008, 04:14:58 am by NikosR »
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Nikos

bjanes

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« Reply #71 on: August 27, 2008, 08:35:27 am »

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DR is often confused with highlight rollout.

The recent sensors, at least from Nikon that I know better, are doing a much better job at having a smooth transition to blown out areas. This is not the result of more DR, but is the result of a better sensor design coupled with more bits to handle the very bright parts of the image.

Cheers,
Bernard
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According to my tests with the Nikon D3, the tone curve remains linear up to clipping and clipping occurs abrubtly. Rolloff in the highlights and shadows is due to the tone curve applied by the raw converter. The top curves are from an ACR rendering with the tone curve set to linear (all settings on main panel = 0, point curve = linear). The second plot is from Capture NX using the Standard Picture Control.

[attachment=8092:attachment]

[attachment=8091:attachment]

Bill
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Ray

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« Reply #72 on: August 27, 2008, 09:42:07 am »

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I think what Ray meant is that the effect is not some absolute limit like a cliff but more of a slope. Your post with the text image clearly shows a worsening of the sharpness just as the theory predicts, but not a 'wall' past which everything is immediately dreadful.

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Thanks for the clarification, Nick. That is exacly what I meant   .

We should not forget the Rayleigh's derived formula which describes the resolution limits of a lens at a particular F stop, a limit which is of great interest to astronomers.

As I understand, in it's simplest form for those who are not mathematicians, as I am not, the resolution limit of a lens at a particular F stop, in terms of line pairs per mm, is given by the formula 1600/F stop.

For example, at F16 a lens can deliver as much (and actually more, I believe) as 1600/16 lp/mm, or 100 lp/mm.

On the basis of approximately 3 pixels per line, the new 50D is capable of only 73 or so lp/mm.

Now I know, even if the the 50D were a foveon sensor without AA filter and were capable of recording over 100 lp/mm, it still wouldn't be able to record those faint lines at F16 because the MTF of those lines is only about 9 or 10%. They've lost about 90% of their original contrast as a result of diffraction. Camera system noise, read noise and insufficient quantum efficiency would all conspire to bury such faint signals.

But what about detail at 70 lp/mm at F16 and say 25% MTF? If such detail is of sufficiently high contrast, glittering black specs in the sunshine, I wouldn't be surprised if the 50D were able to record them in circumstances where the 40D would not be able to, simply because the 40D does not have sufficient pixels and resolving power.

Below is what Norman Koren has to say on the subject. The bold italics are mine.

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Lenses are sharpest between about two stops down from maximum aperture and the aperture where diffraction, an unavoidable consequence of physics, starts to dominate. For 35mm lenses, this is typically between f/5.6 (f/8 for slow zooms) and f/11. At large apertures, resolution is limited by aberrations (astigmatism, coma, etc.), which lens designers work valiantly to overcome. MTF wide open is almost always poorer than MTF at f/8.

Diffraction worsens as the lens is stopped down (the f-stop is increased). The equation for the Rayleigh diffraction limit, adapted from R. N. Clark's scanner detail page, is,

Rayleigh limit (line pairs per mm) = 1/(1.22 Nω)
N is the f-stop setting and ω = the wavelength of light in mm = 0.0005 mm for a typical daylight spectrum. (0.00055 mm is the wavelength of green light, where the eye is most sensitive, but 0.0005 mm may be more representative of daylight situations.) I've seen a simple rule of thumb, Rayleigh limit = 1600/N, which corresponds to ω = 0.000512 mm. The light circle formed by diffraction, known as the Airy disk, has a radius equal to1/(Rayleigh limit).

The MTF at the Rayleigh limit is about 9%. Significant Rayleigh limits are 149 lp/mm @ f/11, 102 lp/mm @ f/16, 74 lp/mm @ f/22, and 51 lp/mm @ f/32. Larry, an experienced lens designer, finds these numbers to be somewhat conservative because the Rayleigh limit is based on a spot, which has lower resolution than a band. His numbers of 125 lp/mm @ f/16 and 64 lp/mm @ f/32 are derived from a Kodak chart he contributed to Robert Monaghan's Lens Resolution Testing page.

Most lenses are aberration-limited (relatively unaffected by diffraction) at f/8 and below. The OTF (optical transfer function) curve in David Jacobson's Lens Tutorial shows how MTF (the magnitude of OTF) varies with spatial frequency for a purely diffraction-limited lens at f/22.
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ejmartin

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« Reply #73 on: August 27, 2008, 10:37:44 am »

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It is my contention that by the time you reach f/11, there will be no difference between a 40D file and a 50D file.  I could be wrong primarily due to AA filter strength, but I'm convinced that the 50D is going to start being diffraction impaired at about f/8.  Losing a third or even half your resolution over a stop will be significant, whether you would call that a "wall" or "gradual" is a matter of semantics.  Anyway, I like your term "Diffraction effect threshold".
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The emphasis on the "diffraction limitation threshold" is misleading, and results in the common misperception of diffraction limitation as a problem. I would turn it around and say that the key issue is instead "pixel pitch limitation" -- larger pixel size results in a wider range of apertures where the limiting factor in system resolution is the pixel size rather than the optics. The smaller the pixels, the smaller the range of apertures where the sensor is the limiting factor in resolution. Why is that a problem? The photographer should choose the aperture for the DOF needed in the image they envision, and if the sensor is not getting in the way of resolution so much the better.

One begins to see where Canon is headed with the 50D. Eventually, it seems likely they are going to offer APS-C or larger sensors with digicam-size pixels, and one doesn't want to record all the pixel values when the Airy disk is several pixels across, as it will be for the narrow apertures one needs for some applications such as macro or landscapes. Canon seem to be offering a more flexible sRAW format (a choice of 1/2 or 1/4 the number of pixels) so that one can dump the superfluous resolution at those apertures and at the same time mitigate some of the shortcomings of the Bayer array sensor.  And when the optics justifies it, the extra resolution is there if one wants it.


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I bet you can tell which side was f/11 and which side was f/16.
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OK, I'll bite.  It looks to me like the image on the right has lower microcontrast (lower MTF) and so should be the f16 image.
« Last Edit: August 27, 2008, 10:44:32 am by ejmartin »
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emil

DiaAzul

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« Reply #74 on: August 27, 2008, 11:42:47 am »

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There is no such thing. The sensors' output is strictly linear (disturbed somewhat by the noise).

Bernard is actually correct. The sensor does exhibit non linearities, especially at the extremes of its response curve, though in practice the output is clipped so that only the most linear part of the sensors response curve is used. This allows uniformity and linearity to be managed and is why when analysing the RAW output data you are seeing a linear response. Typically the non-linearity is less than 2%, but it is still non linear.
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Panopeeper

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« Reply #75 on: August 27, 2008, 03:45:44 pm »

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Bernard is actually correct. The sensor does exhibit non linearities, especially at the extremes of its response curve, though in practice the output is clipped so that only the most linear part of the sensors response curve is used
If this were so, then Bernard could not have observed what he thinks he had observed, could he?

However, I doubt that this is correct in the current context. Here I have to admit, that my doubting is based exclusively on observation, not on the knowledge of the technical aspects of sensors.

The issue is, I think, that we are talking about two kinds of linearities.

One is the response of any given sensel. This is IMO linear, excluding the effect of noise. Of course, if the response is non-linear but it is clipped back to the linear segment, then my observation is worthless.

The other issue is the response of the entire sensor. As I explained above, this can be seen as non-linear in the sense, that different pixels (usually grouped in rows or columns) have different saturation points. This can in fact make 0.5%-1% of the entire range.

I can not explain why, but the greens usually have a lower saturation point than the reds and blues, and often there is a gap between the saturation points of pixels in the two green positions; again, it is demonstrated in the documentation I linked above.
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Gabor

BJL

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« Reply #76 on: August 27, 2008, 03:48:20 pm »

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For landscape photography the increased MP will be useless.
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If the increase from 10MP to 15MP in EF-S were useless for landscape photography, then 15MP or more would be equally useless in larger formats too: try telling that to landscape photographers who are happily using the 1DSMkII or 1DsMkIII or even higher pixel counts in medium format.

The possible trade-offs bertween out-of-focus (OOF) effects and diffraction effects is the same in any format: it is just that with the same field of view (FOV), the same combination of OOF effects and diffraction blurring comes at a different f-stop. In fact, the "equivalent" f-stop is different in proportion to the format size and focal length used, so the same [a href=\"http://en.wikipedia.org/wiki/F-number]effective aperture diameter[/url] or entrance pupil diameter (focal length divided by aperture ratio.)

So what you say about f/11 in EF-S is about equally true for f/18 in 35mm in a comparison between the 11MP 1Ds and the 16MP 1DsMkII.


Note that f/11 in EF-S gives as much DOF as about f/18 in 35mm (comparing with focal lengths giving the same field of view), so in each case one can often reduce diffraction effects by going to lower f-stops while still get adequate DOF for many landscapes.
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BJL

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« Reply #77 on: August 27, 2008, 04:07:29 pm »

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One begins to see where Canon is headed with the 50D. Eventually, it seems likely they are going to offer APS-C or larger sensors with digicam-size pixels, and one doesn't want to record all the pixel values when the Airy disk is several pixels across ... Canon seem to be offering a more flexible sRAW format (a choice of 1/2 or 1/4 the number of pixels) ...
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Maybe so, and with the evidence you have shown us that most of the noise in CMOS sensors arises "downstream" of the photosites, and so hopefully after the "binning" to sRAW modes, such binned output could indeed have noise levels, dynamic range and resolution very close to what is possible from a sensor with fewer, bigger photosites. If so, a win-win for choices between higher resolution and lower noise.

A possible hint of this intention is the prototype sensor that Canon has described in a published paper, with 50 million pixels of 3.5 micron width in a "1D" sized sensor. (It also has ISO gain applied very early, at read-out from photosites to sense capacitors on each column, enhancing options for reducing the effect of downstream noise sources.)

The choice of 1D size is probably because this is the biggest that Canon (or anyone?) can make without stitching, allowing Canon to claim in that paper a record for maximum pixel count on a sensor made without stitching. I doubt that we will ever see that particular sensor in a product, but it is slightly more likely that Canon could offer roughly 3.5 micron pixels in an EF-S sensor, giving about 28MP, with higher ISO lower res. sRAW options like 14MP and 7MP. (And perhaps with no AA filter and very little moiré!)
« Last Edit: August 27, 2008, 04:08:23 pm by BJL »
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lovell

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« Reply #78 on: August 27, 2008, 09:30:23 pm »

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http://www.cambridgeincolour.com/tutorials...photography.htm

Read and learn, and then you can do what Thom Hogan and others (including myself) have done, and do comparisons between various pixel pitch DSLRs at various apertures and see for yourself.



As you can see, a 12 MP DSLR was reduced to no better than a 6 MP DSLR at f/16; I'm not sure why the 12 MP DSLR pulls ahead at f/22 (probably a smoother shutter), but since they both look like crap I hardly care.

As recently as today, Thom Hogan has posted at DPR on this very topic:  http://forums.dpreview.com/forums/read.asp...essage=29080207
You must have done direct comparisons to make such a bold statement.  Why do I think you are blowing smoke?

The issue will be at f/11, and I will bet you that at f/8 you will see an improvement but at f/11 the 40D will pull even with the 50D because the 50D will have become diffraction limited at f/8.
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Nope nope, diffraction is not effected by MP...it's about the pitch of the micro lenses.

And you're wrong about MP not mattering for landscape and maybe if I put it a different way, you'll get it:

I'd rather cut my frame into 15 million pieces then 10 million pieces.

See what I mean?

Better yet, I'd rather cut my frame into 21 million pieces.

Better enlargements, better crops...diffraction is about micro lens pitch, and not MP per se.
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After composition, everything else is secondary--Alfred Steiglitz, NYC, 1927.

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Tony Beach

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« Reply #79 on: August 27, 2008, 11:38:46 pm »

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Nope nope, diffraction is not effected by MP...it's about the pitch of the micro lenses.

And you're wrong about MP not mattering for landscape...[{POST_SNAPBACK}][/a]

Micro lenses can tighten or widen the gaps between the photosites, but ironically tightening those gaps will increase (very slightly) the effect of diffraction.

I didn't say more resolution (megapixels) doesn't improve landscape photography.  However, if more resolution comes at the cost of lowering the "diffraction effect threshold", then you will have to find a way around that limitation, and probably the best solution will be tilt lenses (and shift for good measure).

Now I'm fully aware of BJL's point about the same issue effecting different formats equally -- indeed, I would go so far as to say that the diffraction limits relative to DOF happen at very nearly the same MPs, so 12 MP is 12 MP regardless of format (just go back to [a href=\"http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm]here[/url] and compare the 5D at f/16 to the D2x at f/11 and you will see what I mean).  For me this leads to a simple conclusion, I will get more from purchasing tilt/shift lenses and would gain not much more than larger file sizes by purchasing a higher MP DSLR absent those tilt shift lenses -- YMMV depending on how you approach a scene (if there is nothing close that pushes the DOF, then you are golden).
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