In article <96325.153812U15310@uicvm.uic.edu>, U15310@uicvm.uic.edu says...

>I've heard from at least two people who have purchased this lens, then
>returned it because the zoom slides when the camera is held in vertical
>position!

It does do that, but I am mystified by people who consider that
a fatal flaw in an otherwise amazing lens. If the lens is hand-held,
it is gripped by the wide zoom ring, and there is no problem; if the
lens is on a tripod-mounted camera and aimed REASONABLY close to
horizontal (true for most photos), there is no problem; if the lens
is pointed sharply down (a fairly unusual condition), or is used as a
copy lens vertically on a stand (!!!, a ZOOM!!!;-), there is a problem,
and a bit of masking tape can solve it. Methinks that those who have
a problem with the dread Zoom-Creep would give back a gift of the
Hope diamond if they found a speck of dust on the side...;-)
We take pictures with lenses, not just expect them to pass arbitrary
physical tests, like not self-zooming (or focusing) when pointed
straight up.... Lotsa good lenses do one, the other, or both, folks!
Hope This Helps