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.
