Kent suggested: >Well that is correct except at the widest >setting. If you have a 28-80/4-5.6 lens >and >set the aperture manually at F4 and zoom from >28 to 80mm you will end up at >F5.6 even if the >ring says F4. This is because at the >widest setting the aperture >ring is not >involved in the actual diaphragm function. >The insides of the lens >barrel is what >determines the aperture in that case. It's >actually easy to see the >effect. If you sit at >28mm and change the ring from 4 to 5.6 the >shutter value will >change. If you move up to >around 80mm and switch it between 4 and 5.6 >the shutter >value will not vary at all.
I don't agree. My experience with the F 70-210/4-5.6 on my -5n is that at 70mm, the aperture values shown on the ring correspond to the actual value fed to the meter. At 210mm, each value is a whole stop slower - i.e. f/4 on the ring shows as f/5.6 in the viewfinder; f/32 as f/45. At an intermediate length, say 150mm, the difference is more like half a stop - f/8 becomes f/9.5. Since I seldom use anything but TTL metering, this doesn't matter to me, but for purely manual flash, I'd need to compensate for it. I think Mike's original question was "does f/8 on the ring of a variable-aperture 28-80 still mean f/8 at 50mm?" Well, if all Pentax v-a zooms work like mine, the answer is no. Hope that's some help, Clive. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
