That's good information. I had wondered at what focal length the focus adjustment should be set on zoom lenses. It's obvious that it wouldn't be absolutely consistent throughout the range. But I would hope it would always be close. My lenses seem to show only minor variation in this regard.
BTW, my new DA* 16-50 is very nice. No problems. Hope we all have no problems going forward. Paul On Apr 16, 2008, at 10:04 PM, Joseph Tainter wrote: > My gear came back from Pentax--K20D, DA* 16-50 and DA* 50-135. > Turnaround was just over three weeks, but it took me nearly another > full > week to pick up the package after UPS messed up the delivery. > > I sent all this stuff in because on the K20D the DA* 16-50 would not > autofocus to infinity at 16 mm. It would focus only to about the 2 m > mark. From 18 to 50 mm it focused fine, and focused fine at all focal > lengths on my K10D. > > So now the focus problem seems to be solved. It focuses to infinity at > 16 mm. What was wrong? Can't tell. The work order came back with some > gibberish stating that they "repaired or replaced" various parts in > the > lens and/or camera. I can't tell exactly what they did. > > I sent in the DA* 50-135 because adjusting the focus at 135 mm > caused it > to focus beyond infinity at 50 mm. The work order came back with these > instructions: > > "Please set focus shift adjustment to where it will focus at medium > setting of the zoom range." > > So this is Pentax's official instruction for how to adjust focus in a > zoom lens. Over at dpreview, John Cunningham of Pentax USA has posted > essentially the same instructions. > > I interpret this to mean that one cannot adjust a zoom lens to > autofocus > accurately across the whole zoom range. > > This weekend I'll try to test these lenses again for focus adjustment. > > Joe > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above > and follow the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
