DA* AF problem - diagnostic opinions welcome

Stan Halpin stan at stans-photography.info
Mon Oct 26 21:48:01 EDT 2009


The lens in question: DA* 300/4.

Basic symptom - it does not autofocus on my K20.
Expanded description - sometimes it works when first turned on, but  
then refuses to work when woken up after a Sleep period.

"Doesn't work" = nothing happens. It is not mis-focusing, it is rather  
doing nothing - no response to shutter depression or AF button.
Expanded description of "doesn't work" = not only will it not  
autofocus, but I cannot manually focus either. Focus rings turns but  
nothing changes.
I tried another DA* lens (50-135) and it works flawlessly.

OK, simple issue, right? Lens needs repair.

So, when it isn't working,  I switch the lens, on the lens barrel, to  
MF. I still cannot focus!
So, I also switch the AF/MF switch on the body to MF, and then I  
regain (manual) control.

All pretty definitive so far, it seems that it must be a lens problem,  
and off to Pentax with it.

But when I use the same lens on a second K20, no problem. It works as  
it is supposed to.

Dirty contacts on the lens and/or first body? I cleaned those; no  
change in the lens (mis)behavior.

Any suggestions as to what is going on?

stan




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