See Paul's query below. With my first DA* 16-50, at 16 mm the lens would not autofocus past about the 2 m. mark, even on very distant objects. (I use only the central af point.) At first I didn't worry about it, figuring that DOF would cover the difference. But when I focused manually to the infinity mark, the images were much sharper. I sent this lens, the DA* 50-135, and the K20D to Pentax, and the camera came back set for a universal -3 AF adjustment. That seemed to be a good compromise, and at 16 mm the lens would focus to the near part of the infinity mark. The lens thereafter performed pretty well, but on this last trip to Italy I noticed the problem of edge weakness above 40 mm. Hence it went to Pentax, which sent me a new sample of the lens.
Now I have another sample of the lens showing the same af problem. Tonight if I'm not too tired I'll test it with the standard focus adjustment chart. It's possible that I can correct the problem with focus adjustment. I believe that is what Pentax did when I sent the first one in. I usually keep a skylight filter on each lens, but at the moment there is no filter on this lens. So I know that is not throwing off the af. Joe ----- How does one check infinity focus at 16mm? It would seem that the DOF is so extensive at that focal length, even at f2.8, that it would be nearly impossible to determine accurate focus. I don't think I've ever attempted infinity focus at 16mm on my lens. I'll have to try it and see what happens. Paul On Feb 11, 2009, at 11:59 AM, jtainter wrote: > My K20D came back yesterday. It appears that to correct the sensor > problem Pentax just replaced all or most of the electronics. When I > turned it on, it started up with the initial menu, asking for > language, location, time. Then I had to go into the menus and set > all my preferences again. Now I get to start testing 18 or 19 lenses > for autofocus adjustment. > > The new DA* 16-50 F2.8 has a problem like the last one had. It won't > autofocus to infinity at 16 mm. So even in newer copies of this lens > there are problems. I will try to correct this with the autofocus > adjustment, but if that doesn't work it will have to go back to > Pentax--again. I'm getting tired of this. > > 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.
