[AdrianM]

Something I have just found and still have to go through the trouble-shooting. With K5 and Sigma 500 f4.5 APO DG EX, in AF.C and multi-point focus, the focus 'gives up' if the subject isn't pre-focused. When I say 'gives up', it goes to the minimum focus distance and does not hunt across the range, just 'twitching' in place. Once focus lock is obtained, it tracks normally, but once lost has to manually be refocused. Centre spot focus works just fine. I have recently updated to Firmware 1.14, and the multi-point focus mode is not something I normally use, so suspect that it might be something with that. Am yet to try other lenses.

Anyone else out there with this experience ?

[AdrianM]

A bit more testing:
- No problem with the 500 f4.5 on the K20D, so can exclude the lens from being the problem
- K5 works just fine with Sigma 100-300 f4 DG EX

Sort-of says to me that there is a K5 firmware problem with the Sigma 500 f4.5 noting I have not seen this behavior previously and really haven't used multi-point focus since I upgraded the firmware to 1.14.