"Jim" writes:
> There is no "standard" lens for any format. There is a "normal"
> lens whose angle of view more or less has the same angle of view as
> the sharp area of human vision.
I think a "normal" lens has about 45 degrees of coverage because
that's the simplest to make optically for a given f/ratio. For 35mm
FF, that's around a 45mm focal length. The film to flange distance on
a 35mm SLR system is chosen so that the image circle of that 45mm lens
is about the right size for the film frame. However, with a DX lens,
because of that extra distance, they need a more complex optical
design to get the same angular coverage.
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