Originally posted by Rondec The issue is early diffraction. At present, 7D shooter can't shoot over f4 without diffraction setting in.
Diffraction happens independently of pixel pitch. It is caused by the aperture size and the wave-like nature of light (it can be particle-like as well, but let's not indulge in the Copenhagen interpretation of the nature of light
).
If you increase the pixel-pitch, i.e., sensor resolution you'll be able to see the diffraction effects when pixel-peeping. However, when comparing at the same output size, the higher-resolution sensor will always look better / sharper.
At f/4, you'd need 52MP to see the diffraction effect and a lens that is diffraction limited at f/4. The vast majority of lenses are not diffraction limited at f/4 but exhibit optical aberrations overshadowing the diffraction effect.
The 7D is often criticised for its IQ. I believe it wouldn't be the camera for me but I don't doubt for a split second that "too many pixels" are to blame. It seems Canon has an issue with using two different channels for the green component of the matrix and matching them up takes away from the resolution. IIRC, GordonBGood discussed this ages ago on DPReview.
Originally posted by Rondec This was based on something that Klaus said about 15 megapixel cameras (APS-C) hitting diffraction at f5.6.
For green light you need 27MP to capture diffraction effects at f/5.6 on APS-C. See
Do Sensors “Outresolve” Lenses? (Tab. 3).
I personally like high-resolution sensors because they (everything else being equal) yield finer-grained noise and have better cropability. Ever found an image in an image and wished you had enough resolution to crop into it? Moreover, in order to increase focal length, I'd rather have 1.4 x resolution I can crop into than put a 1.4 teleconverter between lens and the camera. There is no teleconverter which works as perfectly as cropping.