On Fri, 13 Mar 1998, Ian M. Stewart wrote:
> Excuse me being dense, but to what do you refer? I have no experience with
> zoom lenses at all, but guess that you mean the reduction in light
> transmission as the magnification is changed?
No. The fall-off problem has to do with the transmission of light
across the lens surface. More light is transmitted through the center than
towards the edges. This can be quite significant, and is often referred to
as "vignetting", because the effect is similar. With color print film, a
little fall-off is masked (though still visible in shots of uniformly
toned high key surfaces), but not so with slide film. There is noticeable
darkening towards the corners. In the case of the 35-70/3.5-4.8 S-Zuiko,
this is a problem, because it doesn't go away until f/11-16.
Plus, other compromises with most zooms involve reduced SQF at th
wider apertures (much less so with the high-end zooms, like Zuiko
35-80/2.8, Canon 28-70/2.8 L, Nikon 35-70/2.8 D, Contax 28-85, and
others), and don't become sharp until f/8 to f/16. Wide open, many (like
this S-Zuiko) aren't very sharp. Sharpness isn't everything, though, and
understanding that the numbers in lens tests don't tell the whole story is
of paramount importance to any photographer.
> > I can't believe companies don't offer a
> >corrective filter for lenses like this one. It'd be worth it.
This would be a graduated ND filter, with a pattern to match the
fall-off in the zoom, but reversed, so that in the image, the illumination
woould appear perfectly even across the frame. Some view camera lenses,
like the 45/5.6 Super Angulon, have filters that match its fall-off.
*= Doris Fang =*
############################################################
| This message was delivered via the Olympus Mailing List
| To receive the Digest version mailto:listserv@xxxxxxxxxxxxxxx
| with "subscribe olympus-digest" in the message body.
| To unsubscribe from the current list mailto:listserv@xxxxxxxxxxxxxxx
| with "unsubscribe olympus" in the body.
| For questions mailto:owner-olympus@xxxxxxxxxxxxxxx
| Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html
############################################################
|