Steve wrote: >It's easy to explain. Ninety-nine times out of a hundred, you select a lens with a particular focal length for a particular photo >because it provides the angle of view you want for that shot. But lenses aren't identified in terms of angle of view, they're >identified in terms of focal length. This leads to people measuring angle of view in millimetres, which is actually perfectly >reasonable, as long as everyone understands that they're referring to the equivalent AOV that would be obtained by using a >lens of that focal length on a camera with a 35mm-size sensor. > >Pedantically, measuring angle of view in millimetres is abhorent, but given that it's a much more convenient measure for the >majority of photographers, I personally don't have a problem with it as long as everyone understands what they're doing. :-)
Well put. The focal length of a wide angle lens for medium format is not going to be a wide focal length for 35mm and a wide 35mm lens is not wide for an APS sized sensor. The corollary is also true. No one is disputing that focal length may well be the same in each case but it is what that particular focal length can do in any particular format that matters. We all like to frame our shots to our satisfaction at the time of taking the photo and for that we choose the appropriate focal length lens. If for an APS sensor a 200mm gives me the framing I want (and that happens to be equivalent to a 300mm lens for 35mm) then I don't give a rats if on someone's 4x5 that 200mm would be a semi-wideangle lens.
