Very few modern zooms are perfectly parfocal. It is best to focus at the focal length you are going to use.
I haven't experienced any obvious focusing errors with the DA21 on either DS or K10D bodies; however, the focus is more accurate on the K10D. Finding the precise AF sensitive area is often a little tricky with a wide lens, however, and can cause some focus inaccuracy. G On Jan 30, 2007, at 6:57 AM, Rick Womer wrote: > Brian, > > In the autofocus era, I doubt that many (if any) > "zooms" are true ol'-fashun focus-preserving > zooms--they all seem to be variable focal length > lenses. > > That's certainly true of the lenses I can afford, > anyway (including the fairly pricey 24-90, 16-45, and > 10-17). Don't know about the high-class glass like > the 70-210/2.8. > > Rick > > --- Brian Dunn <[EMAIL PROTECTED]> wrote: > >> >> I received a 21 Limited. Center only autofocus >> always greatly back focuses on >> both ist-DS cameras, more on one than on the other. >> The 45 degree focus >> chart showed the 21 Limited back focusing almost off >> the far end of the >> paper. >> >> I tested other lenses and found that they all back >> focus when set to wide >> angles. The amount seems to be proportional to the >> angle. For example, you >> could set a 16-45 on a tripod, aim at something 7 >> feet away, zoom in to 45mm, >> focus, then zoom out and focus again. The more you >> zoom out, the more the >> autofocus changes. >> >> All this time I have been zooming in, focusing, >> zooming out, then taking the >> picture. It works fine until you get a wide prime >> like the 21 where there is >> nothing to zoom. When aimed at something across the >> street it tries to focus >> past infinity and hits the stops. >> >> Research on the Internet finds discussion about >> adjusting three screws under >> the base plate of the DS. These hold the auto focus >> sensors and you can >> adjust for front or back focus. >> >> So I'm wondering if anyone here would care to take a >> 16-45 or 18-55 or the >> like, zoom in and aim at something across the room, >> see on the focus scale >> what distance it chose, then zoom wide and focus >> again to see if it changed. >> Do all Pentax digital cameras back focus at wide >> angle? >> >> Has anyone here tried the adjustments under the base >> plate? >> >> Has anyone had a Pentax repair center successfully >> fix this issue? >> >> >> Brian >> >> -- >> >> Brian Dunn Photographic >> http://www.bdphotographic.com >> >> -- >> PDML Pentax-Discuss Mail List >> [email protected] >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> > > > http://www.photo.net/photos/RickW > > > > ______________________________________________________________________ > ______________ > Looking for earth-friendly autos? > Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center. > http://autos.yahoo.com/green_center/ > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
