Taz wrote: T>If the zoom is set on the shortest focal length then, T> and only then with the exception of some lenses that claim f stop stays the T> same, the cameras shown f-stop will equal what it says on the aperture ring. T> I guess I would question the accuracy of doing this type of test in this T> manner on any zoom lenses.
Taz, The 28-70 is a constant aperture zoom. The 80-320 was tested at 80 setting. Focal length was invariant. T> I've done some testing by setting the rig up on a tripod aimed at a steady T> unchanging scene with a constant midtone color for a large area. I would T> use aperture priority to select an aperture with the ring set on "A", making T> sure it was not in between stops but at a full stop setting corresponding to T> one available on the dial. If it's a zoom use again only the shortest focal T> length, primes again work better. Note the corresponding shutter speed T> selected by the camera. Change the aperture ring setting to the same one T> shown in the camera, and again note the shutter speed settings for any T> change. I would think theoretically they would be the same if all is well. You can bet they would be the same, always. The whole problem lies not in what aperture/speed the camera displays, but in what aperture is effectively used when closing down the lens. You can't figure this without actually looking through the lens... Servus, Alin
