In article <4eq8ro$jsf@merkurius.lu.se>, johannes.amilon@jur.lu.se says...

>How can a zoom lens keep a constant aperture over the entire zoom >range? Since aperture and focal length is (at least I thought so...) >proportional, shouldn't the aperture change when the focal lenght does?
>BTW : Any comments on Nikon 80-200/2,8D w/N90s???

Last first: very nice!
If you look into a constant-aperture zoom as you zoom it, you can
see what is done to make the aperture constant: the designer has
the diaphram opening change as the lens is zoomed.
Hope This Helps