Originally Posted by douglasf13
but we're talking about usable equivalents, here.
No, we are not. A lens basically is broken down to focal length (angle of view) and aperture (exposure). Period. When I chose a format, I work in that format. I don't chose an 8x10 and then make all kinds of conversions to get it to work like my 35mm Nikon F.
Equivalency models are basically flawed. First, it assumes equal sensor response. Since when has that ever happened? Second, it really is not equivalent because it can never be--hence exposure is always different and focal length can only work at one object distance. Or in other words, the folks making the equivalency model are simply setting the biases based on a perceived process of interdependent variables whose relationships are fixed as somehow objective rather than realizing that variables are actually independent and can be combined in a large combinations of ways (and in ways that don't fit their model) determined by a photographer.