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 p.5 #8 · DPreview of 50D is flawed ..please read | |
n0b0 wrote:
There is no such thing as "the diffraction limit", it's not like the image stays sharp up to a certain f-stop and just get blurry afterwards. Diffraction increases gradually as we stop down. It's up to the shooter to decide at what point it is acceptable. Obviously pixel peepers will be limited by their own misconception much earlier than others.
I agree. However, apparent sharpness and resolution are two different things. You can increase apparent sharpness by sharpening in post-processing but you cannot increase actual resolution. I am not talking about the number of pixels but the amount of actual subject detail.
Whether you need the pixel-level detail, depends on what you do with the image. Low level of detail in the image limits how large you can print and still have enough detail.
Also, if your pixels do not contain any real information, why store the files with the "empty" (=devoid of real detail) pixels? In that case, using a smaller resolution in the camera would produce the same results when printing. In your first example, Medium size would capture all the same detail as Large does but in a file with a size 1/2th of the large one. If you need more pixels, you can uprez the file in Photoshop.
Edit: I performed an experiment with this file and it seems that 50% size dropped some actual detail while 75% size did not. My test was done by first downsizing the image to 75% and the uprezzing that file to 133% to regain the original pixel dimensions. I then flip-compared that file with the original. It was hard to get exactly the same sharpness - my first attempt actually looked better than the original!
With very sharp originals, even 200% size looks good, so there is some potential that the camera has but that gets lost through diffraction. Whether you really need that much resolution, is another question, of course. However, consider it as a digital 2x teleconverter with no loss of light, and you'll see the benefits, even to non- pixel peepers. 
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you just made me laugh out loud at work.