[mongrel]

I own a Pentax 645D which has recorded around 2000 shutter actuations and appears in perfect condition.

The problem I have is that every time I turn the camera on the autofocus will hunt by scrolling past the point where it is in focus to where it is still unfocussed and then scrolling back again past the point of being in focus and continuing this hunt back and forward for many cycles, sometimes for up to 5-10 minutes before eventually locking in perfect focus. Once the point of being in focus has been reached, it will then focus perfectly and in very quick time on the 80mm-160mm lens I own.

This does not seem to be related to the lens as I have tested it with three autofocus lenses in total (2 others from a camera store ) and the camera exhibits the same action with each lens. Again, once the focus locks in it works perfectly until I turn the camera off and upon turning the camera on again, the problem repeats itself.

I have used both shutter button focus and back focus buttons with no difference. I have done the two (soft or custom function) camera resets mentioned in the instruction booklet to no avail.

I am wondering if anyone has had this problem and whether anyone is aware of a "hard" camera reset that goes further than the 2 custom function resets that may solve the focus issues or if anyone has any other advice on how to resolve this issue.

[chrism888]

Check the contacts on the camera mount are clean, an alcohol wipe should do the trick, clean the lens contacts as well.

[mongrel]

Yes Chris, have already tried that but made no difference

[leekil]

This seems a bit unlikely given the characterization of the problem, but is there dust in the focus sensor?

[yucafrita]

This seems a bit unlikely given the characterization of the problem, but is there dust in the focus sensor?

Yeah, maybe there is dust in the camera which blocks the AF sensor. Try to blow it out.

[mongrel]

Already had technician do that too. Made no difference

[yucafrita]

Did you try to reset the camera and is the latest FW installed? Other than that, maybe a faulty battery. Sometimes, this produces the most weird incidents. If all this is ruled out, I would say off to Pentax service for a check.

[mongrel]

Latest firmware is installed but have not tried a different battery (only have 1) so that may be worth a try. As mentioned, I did the 2 custom function resets with to no avail, but am wondering if there is such a thing as a "hard reset" that isn't mentioned in the instruction book.

[Fries]

I've had a similar but slightly different experience with my K-3 after prolonged use near seawater. The shutter button was stuck halfway and because of that after start up the camera started focusing right away. The difference is that whilst that was happening I couldn't acces the menu. But you have successfully changed the focus to back button focus so you do have acces to the menu settings.

But it might be worthwhile to check if your 'buttons' have become somewhat 'sticky' too.

[mongrel]

The camera doesn't focus as soon as it's turned on, I have to depress either the shutter or AF/ON button to get it to focus so I don't think a sticky shutter button could be the problem

[672]

its as if its in AF calibration mode at start up.

[mongrel]

So, is there any way of preventing it from AF calibration mode on start up???

Btw, in response to a previous post, I tried with a different battery and it made no difference to the problem.

[rdenney]

Have you taken the lens out of autofocus to stop the hunting? If so, do you get the focus confirmation light when manually focusing? Does it focus properly when you put it back into autofocus?

I had this experience once where the autofocus started hunting. Taking the lens out of autofocus stopped it, and it worked fine after that. It may be the lens.

Rick “many of whose lenses have far more experience than the camera” Denney