Ken Waller wrote: > Curious if you were able to tell visually if you had a focus issue before > the correction?
I've been well aware of the front focus problems with my FA* 85/1.4 (showing up since the MZ-S times, through *istD & K10D) and now I've finally been able to fix it. The same happens with the 31 Ltd and a Sigma 70-200/2.8 (front focusing only at its lower end). Those problems were already obvious with the K10D and remain the same with the K20D, before I did AF data correction. For some reason, with my previous cameras I didn't spot the problem with the two 50mm lenses. > If so can you now see an improvement. Definitely yes. Two more comments of AF calibration. 1 - Several years ago, I also tested two more samples of the FA* 85/1.4 and got the same front-focusing problem with the MZ-S, with minimal sample variation. On the other hand, three different samples of the F 70-210 lens had no problem with my MZ-S, showed heavy front focusing with my *istD and were back spot on with my K10D. Not yet checked with the K20D. OK, not enough data for serious statistics, but apparently some lenses keep the same problem irrespectively of the camera model you use them with. With other lenses, issues come and go depending on the body. So you cannot tell for sure whether it's a camera or lens problem. I'd think of it as a mismatch problem. It's a complicated world... 2 - Warning: under certain conditions, the AF test can give you erratic results. I'm rather convinced it mainly depends on the contrast of the situation (test chart+lighting+lens in use). With a given lens and a given lighting, it appears that when the camera "thinks" the contrast is OK, then it stops focusing without trying to get it even better. That's probably for preventing the risk to go back and forth before focusing properly. Unfortunately, this way you'll have front focusing if you are coming from a closer focus setting and you'll get back focusing when you come from a farther focus setting. Under certain lighting conditions, you can have such problem with a given lens and no problem with another type, probably depending on how contrasty the lens is. So I'd recommend to always perform two focusing tests for each lens correction, one coming from a closer focus and another one from a farther one. If you get the same focus, you are doing well and you can apply the needed correction. If you get different results with the two focusing directions, you are in that odd condition and you have to change the lighting of the test chart for getting useful results. Dario -- 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.
