Originally posted by benjikan Just got the response from Pentax via their head office in Germany. They confirmed that there is a back focussing problem with the 21mm Limited exclusively. They offered to set up one of my bodies to work in conjunction with the lens, which I refused. I do not wish to take up one body exclusively for that lens. I am waiting on a firmware fix or a chip set change for the lens. I will use it in manual focus only. They are sending me back the two bodies and the two lenses i.e. the 21 and the 16-45 which didn't have a problem and focussed perfectly on the "0" calibration point. I will wait for the 16-50 f2.8 which I should have in ten days to use in lieu of the 21mm Limited. If it is anything like the Canon 17-40L lens which I used on 80 percent of my magazine work, I will probably do the same with it.
Ben
The DA 21 does seem to have a generic BF problem. I have tested 2 samples and they were identical. For most purposes it doesn't come into play as the DOF of the lens is quite large even at f3.2 and in many shots it will not be noticeable as the near limit of acceptable sharpness will be just within the focus point.
Here is a test at f3.2
At smaller apertures and with reasonably distant objects (as in the beach shot posted by Andy) it wouldn't show up, in fact it will give added depth of field behind the focus point which could be beneficial.
It will obviously be quite critical at close subject distances and at, or near, max aperture, which is how I suspect Ben is working with this lens.
The FA*24/f2.0 also has a tendency to exhibit a similar charactaristic, but is less severe, but as it's an f2.0 lens it does show more readily. This is why some people claim it is soft at wide apertures, usually it is slightly OOF. Here is the test at f2.0.
Unless Pentax feature the same kind of menu focus calibration settings as allowed by the new C*n*n 1D mkIII (which they could do, the capability is in the debug subset. Maybe they will see fit to bring it in as a firmware update?), the lens itself will probably need to be re-calibrated.