DA* AF problem - diagnostic opinions welcome

Leon Altoff leon.altoff at gmail.com
Tue Oct 27 07:22:45 EDT 2009

Hi Stan,

It could very easily be a problem with your K20.

The DA* 300/4 may have a larger motor in it than the 50-135 which
needs more current to operate.  A partly faulty power regulator in the
camera that supplies the lens may overload with the 300 and not the
50-135 due to the increased current (and explains why it sometimes
works just once when all the circuitry is cool).

Unless you can prove the camera doesn't work with any DA*300/4 lenses,
the camera and lens need to go in together for service.  It may be a
slightly out of tolerance lens affecting a slightly out of tolerance
camera.  There are unfortunately a lot of possibilities for problems
and the tech will need to be able to recreate the problem if he is to
have any hope of fixing it quickly and in one visit.

Look upon it as an excuse to get a K7 while the 20D is in for the service :)


2009/10/27 Stan Halpin <stan at stans-photography.info>:
> 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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