Firmware update side effects?

Whilst browsing around found some comments on the Pentax Forum.com website that some are finding that the latest update has improved focus sensitivity. Although it seems unclear if this is purely on the mechanical drive with the later models, however I didn't notice any reference to the SDM drive.
Certainly with my K10D and 16-45 this seems to be true, although not having it long or being used to it's normal, it seemed quicker.

Here's the twist my Sigma 150-500 in good normal light remains unchanged but in early morning/misty conditions it's lost the plot.
Manually focusing on shipping containers in the Solent it was leaving the focus point and hunting.

Anyone else having these effects?

Alan

Early morning misty conditions with a distant subject sounds like a lack of contrast; the life blood of the autofocus system! If you've got the focus right manually, just disable the autofocus in these conditions.

John

hi alan i have the same problem with this lens in poor light and have missed loads of good shots because of it ,especialy when youre tracking a red kite in the sky it goes all over the place so i have to manualy adjust it but i can live with that as the plus side is in good light it is very good brian.

The containers were red and white, sun was up at 08.30 and I expected it to hold.
Really grey mist would be zero contrast which I've had with still water on grey horizon.
As with all long lenses once focus slips off target hunting begins, and the longer the more critical.
I've chased the kites with moderate success with the 80-320, 500 mirror I just couldn't keep up

Brian
I agree good light it is a dream although I expected faster reactions (not to something akin to the 16-45)? but so much less hassle than the mirror.

Thanks for the replies guys.

Alan