>> Surely the whole point of constant-aperture zooms is that they are >> equally fast at both ends of the zoom range, not just at one end? >> > No, the whole point is that the aperture does not change throughout the > zoom range. I'm not sure but I think a non-constant zoom could be > designed that was of equal (equivalent?) speed at both ends.
I suppose that's true, Mike - for example, a 70-210 zoom could be f/4 at 70mm, and f/4 at 210mm, but could be f/3.5 at 135mm, say. However, that would certainly be an unusual design, no? (At least, I myself have never seen anything such as that.) Fred
