Originally posted by stevebrot This is so true. With medium and large format, small apertures are a fact of life if you need deep DOF. This is true even for cameras with movements if you are at all close to the subject. Steve
I concur, with 8X10 format my Rodenstock 240mm f/5.6 APO Sironar performs optimally at f/22 - but often I find stopping down to at f/45~64 is necessary for landscapes especially with camera movements used for near/far compositions. Photographers with fixed focal planes and smaller sensors count your blessings!
Originally posted by chicagonature What I'm asking is, do digital sensors become "diffraction limited" at a different aperture than film (all other things being equal and assuming a very high quality lens)? If so, which factors matter and how do they matter: anti-aliasing filter, size of pixels, pixel density, microlenses to better capture the light?
It would have to be one hell of a lens but even the greatest lenses ever made succumb to diffraction. And no, digital sensors are not diffraction limited**. For digital sensors there is the nyquist limit* - the amount of resolution a sensor can sample. Microlenses only increase the amount of photons a single pixel will receive - they have no real impact on resolution as such. The AA filter attenuates signals that approach or exceed the nyquist limit to prevent aliasing the AA filter applies this to all frequencies of light equally. Diffraction is also dependant on the frequency of light, with higher frequency light (E.g :ultra violet,violet,blue)being affected less than longer ones(yellow orange,Red, Infared).
*defined as being one half of the sampling frequency (in this instance #pixels/mm)
**One of the reasons why diffraction wasn't considered a huge problem with film is because there were often bigger problems reducing the chances of achieving maximum resolution e.g photographic technique, film flatness, correct alignment of the ground glass relative to the film plane, focus accuracy - just to name a few. The only situations where diffraction has always been an issue is macro photography - if you stop down too much you will lose image quality - if you don't stop down far enough the subject mightn't be recognisable.