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
