Originally posted by aurele to get something equivalent to 43/1.8 ltd on film, on digital ?
Originally posted by Marc Sabatella I would assume that as you get wider, making fast lenses is increasingly difficult - they certainly get increasingly larger and more expensive when they do exist. I also assume registration distance affects this - a camera with a shorter registration distance (like a Leica rangefinder or a micro 4/3 digital) could allow fast wide angles to be built somewhat more easily. Although there tend to be IQ issues especially in the corners with many such designs: the type of designs needed to make wide angle lenses for longer registation distances actually often roduce better IQ.
The real question is, why would need an "equivalent" of 43/1.9 on film? Sure even a 28/2.8 on APS-C digital is alrady capable of faster shutter speeds for a given noise level than the 43/1.9 on film. And in cases where one is specifically going for shallow DOF effects, I personally find that focal length tends to not be quite so important a consideration, because we are usually talking about carefully posed "art" shots where I can construct a scene that will work well at a longer focal length just as easily. True, not always the case, and for those who really rely on being able to shoot extremely shallow DOF at a large variety of different focal lengths, APS-C DSLR's are at a distinct disadvantage compared to FF or to cameras with shorter registration distances.
I'm not really interested in replicating 43/1.9 on APSC. I'd love to have fast 28 for my EOS 1D MkIII. On APSH sensor (1.3x crop) 28mm gives you the FOV of 35mm (or at least as close as one can get) and those who know me from my Pentax hey day, know that I'm sucker for that FOV (for those who don't know me, I used to have FA*24/2 for K mount APSC and loved it...) For now it looks like I'm going to have to settle for 28/1.8