Barry B. wrote sometime back:
<< I've always worked on the assumption that the glass controls image
quality and the body only controls exposure. >>
Now that I'm back from the wilds of SW Utah and a spur of the moment 6
day photo shoot:
A very important consideration in body design is focus offset. Since
most lenses have curvature of field, bodies are designed with a certain
amount of correction away from the theoretical film plane. It is
entirely possible that the focus offset in a OM-2000 differs from that
of a OM-2S/3(Ti)/4(T)(Ti) and from that of a OM-1(n)/OM-2(n), not to
mention the OM-10, G, F and PC.
Typically, designers measure the curvature of field in their most
popular lenses. They then design the body so that the arc projected by
those lenses has its midsection corresponding to the film plane. In
another words, focusing on the center of the image DOESN'T bring the
center into perfect focus, it brings detail half-way out into perfect
focus. The corners will be slightly underfocused and the center slightly
overfocused - which represents the best compromise possible. They only
better solution is to electronically couple the lens and body so that
the lens tells the camera its curvature of field and the camera
compensates for it. Obviously a solution only for auto-focus cameras or
those with moving film planes, like the Contax AX.
Gary Reese
Las Vegas, NV
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