I suspect that back and front focus problems are almost always the fault of the camera. I too have noticed the hysteria on the Pentax forum. It's the result of some real problems that have now caused paranoia and a search for problems where none exist. Some DA* 16-50 lenses had a manufacturing defect that caused an uneven focal plane. In other words, the right side of the frame might be in focus, while the left side was not. This was a lens problem, but it seems to have been relatively rare and confined to early samples. However, a second condition has complicated the situation. It seems that early K10D cameras were not properly set up for USM, and the firmware update didn't do the job. These cameras backfocused with the USM lenses. But it's apparently a simple fix, and it's not a lens problem. However, the mindless zombies on some forums have blown all of this way out of proportion. As you say, they test every lens, usually handheld and in questionable conditions, and curse and complain. It's an ugly situation, although brought on in part by some problems Pentax created. Paul On May 6, 2008, at 7:30 AM, Andreas Pfotenhauer wrote: > hi, > > i recently followed a discussion in my favorite forum (bulletin > board?) > where a guy who had bought a DA 35/2.8 Limited was very disappointed > because he found the *lens* to have severe back focus on his K10D > while > on his K20D it seemed to work just fine. > > As far as i understand it (with my limited optical knowledge), a lens > can (and does) produce various forms ob optical aberrations, but if > the > "virtual image" is not directly on the sensor but in front or behind, > then it's simply not properly focused, isn't it?! So the AF of the > camera would be to blame for not acting accurate or, as second > possibility, sensor, AF sensor and/or focusing screen are not leveled. > I was asking if someone with a deeper understanding of the optics > could > confirm or denial this, but no one was able (or wanted) to, thats why > I'm asking here now :-) > > The reason why I'm so interested in this is: a increasing number of > ppl > in that forum now test their newly bought lenses with a printed test > chart under more or less undefined light conditions, of course they > find > some back- or front focus (of you look hard enough you surely find > something to worry about, I'm 100% convinced), and then they send > their > lenses back, open new threads in the forum where they loudly complain > about lens qualities, unsettle some more who start testing their > lenses > ... you get the drift. > > I would be deeply grateful if someone could shed a light on this, so > this can be settled once and for all. > > Free beer is offered if that one will ever visit Frankfurt, > Germany ;-) > > cheers > Andreas > > > -- > 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.
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