Originally posted by Denny Got my one from adorama and obviously it is not a very good copy. At 2.8 and 16mm I have to take a couple of shots to get a sharp image. At 16mm and 4.5 everything is fine.
Serial number is 9019078.
Itīs ridiculous what pentax is doing. After that long time I thought everything should be fine now, but itīs not, and they didnīt even recall all the lenses. Why? Instead of recalling, they brought the K20D which has the focus correction thing. How stupid is that?
The "focus correction thingy" you allude to is actually a feature to correct AF lenses that have a tendency to BF or FF. Nikon and Canon also have this feature on their *top* spec models like the D300 and 1DS MKII etc as they *also* have BF and FF issues. We should be thankful that Pentax have seen fit to include it in a model costing alot less than these two examples.
Lens BF and FF issues are quite common in *all* manufacturers lenses and there have been many threads dedicated to these problems on forums of *all* camera manufacturers.
The DA*16-50 f2.8 has some issues, yes, but they need to be taken in context when compared to other manufacturers. This of course doesn't absolve Pentax from trying to have the best QC they can, but also do not unfairly denegrate Pentax as if they are the only ones with QC issues with BF/FF in their lenses.
The interesting thing to remember is that a zoom may focus fine at one end of the zoom range but not be so good at the other end. This phenomenon can be again also evident across *all* manufacturers. The reason *may* lie in the fact that the different colour wavelenghts of light converge at different points - chromatic aberration - and in a zoom this all the more a problem as because when you alter focal length, the the design parameters that were used to fix chromatic aberration at one focal length may not work for others. Zooms are therefore a compromise and the more there is a difference between the short end and the long end of a zoom range, the more there maybe a problem.