My defective DA* 16-50 is ready to go to Pentax to correct the fact that it won't autofocus to infinity at 16 mm on the K20D. The K20D has to go with it.
Before sending them off I thought I would check the focus asjustment of the DA* 50-135. I tested it at 135 mm, figuring that the most rigorous test would be at that focal length because that's where the depth of field is smallest. It turns out that an adjustment of -4 gives the sharpest distance focus at that focal length. But then I noticed that when I zoom the lens to 50 mm it now autofocuses beyond infinity, and the images are not sharp. Arghhh! Okay, I guess the DA* 50-135 has to go to Pentax too to be calibrated to the K20D. But this is disturbing and frustrating. I have been concerned that it may be difficult or impossible to adjust the AF of zoom lenses through the K20D--adjusting for correct focus at one focal length could mean incorrect focus elsewhere. What I have seen so far (with both DA* lenses) confirms that suspicion. But there are larger implications: 1. Does this mean that I have to give up using autofocus zoom lenses if their focus cannot be uniformly adjusted? 2. Does this mean that every time I buy a new camera I have to send the body and all of my zoom lenses to Pentax to be calibrated to each other? 3. Does this mean that every time I buy a new zoom lens I have to send it and all bodies currently in use to Pentax? Or did I just get three bad DA* lenses (this is my second DA* 50-135) and two bad K20D bodies? That's about $3000 worth of gear that I can't use. (Yes, I know, some of you will want to reply that your zoom lenses work fine. Please don't.) Frustrated, frustrated, frustrated. Joe -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
