You wrongly assume that the 50D will not lose acuity at f/11 and will still show the hands on the clock. If the hands can no longer be seen at f/11 on the 50D, then you have gained nothing over the 40D.
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Tony,
It's
not a wrong assumption that the 50D will not lose acuity at F11 or F22 or any aperture you wish to nominate.
The acuity of the 50D sensor is fixed. Only the lens will lose acuity as it is stopped down beyond F8.It's been mentioned several times in this thread that there is some evidence that the higher-pixel-density sensor can continue to provided marginally (perhaps very marginally) greater detail all the way to F32, despite the fact that the theoretical calculation of the size of the Airy disc at such apertures suggests there is nothing to be gained.
My own experience suggests that the contrast of the target will also affect any test results significantly. This is another source of confusion which (for example) prompts many questions about the effectiveness of 1.4x and 2x extenders with a particular lens.
Such questions can never be answered definitively, because it always depends... depends on the contrast and detail of the target as well as the quality of the lens.
After acquiring my Canon 100-400 zoom and 1.4x converter, I took many test shots of distant subjects, with and without converter at 400mm. Even at 200% magnification on the monitor, often I could not see any improvement in detail or sharpness.
However, when shooting closer subjects of high detatail and contrast in bright sunlight, there was always a noticeable improvement using the 1.4x extender.
I imagine the same principle applies when using small apertures with high-pixel-density cameras. There is no brick wall, just a gradual loss of contrast as one stops down. At some point, with a low contrast subject, one will be unable to perceive any improvement in detail or sharpness from the higher-pixel-density sensor. Change the subject (or target) to one of very high contrast, then detail that previously was indiscernible at the same F stop (say F11 or F16) becomes discernible.
I can to some extent sympathaise with your point of view. I was also of the opinion that there's nothing to be gained at diffraction limited apertures with the higher-pixel-count cameras. This is of some concern to me since I have my eye on one of the next 24mp FF cameras which have approximately the same pixel density as my 40D. I was curious if any purpose would be served at F16 and F22, apertures which I can use with my 5D but would hesitate to use with the 40D.
Some of my test results can be found at [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=26420]http://luminous-landscape.com/forum/index....showtopic=26420[/url] , a thread started by dwdallam who was apparently concerned about the performance of his 1Ds3 at such apertures.