"S.Ross" <stevenross@mac.com> writes: > Sorry if this is a dumb question. > When you get a spec. for a lens, > for example: 24-70mm f3.5/5.6 > I know the f3.5 is the speed of the lens, > but why is the 5.6 listed? It's a variable aperture zoom. f/3.5 at the wide angle end (24mm) and f/5.6 at the telephoto end (70mm). In the simplest construction, at the telephoto end at least some of the lens is further away, so if the actual size of the aperture in mm stays the same, as a proportion of the focal length it goes down. Brian Chandler ---------------- geo://Sano.Japan.Planet_3 http://imaginatorium.org/
