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01-04-2012, 09:14 PM   #1
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Help: A50 1.7 not working properly in manual mode


My A50 f1.7 is most likely my favorite lens in my humble bag. Attached to my trusty old K100D Super, it has produced some of my best images.
I like to take my film bodies out for a spin every once in a while. I usually go to the A50 f2 for this. This time, I put a black and white roll on my K1000 (23 years with me and counting) and a color film roll on my P3. So the K1000 got the A50 f2 and the P3 got the A50 f1.7, on loan from my DSLR bag.
But I couldn't make the 1.7 to work manually. No matter what seting the aperture ring was in, either A or any other manually set aperture, the P3 kept displaying "P" program mode. I switched lenses and the A50 f2 works prefectly fine in the P3. Program mode in A, manual mode elsewhere. I never saw this before since I use it in Av in the DSLR.
I cleaned the contacts to no avail. Works perfectly in A mode.
What can be causing this?


01-04-2012, 09:29 PM   #2
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The P3 doesn't have Av mode AFAIK, you have to be in M.

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01-04-2012, 10:11 PM   #3
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I happen to have all four of those items and repeated your procedure as you described.

I agree that the A50/1.7 should display "M" with the aperture ring not in the 'A' position on the P3. (The P3n is slightly different.)

Have you tested the manual/auto functions on another PK/A or DSLR body? The aperture ring may be stuck (electrically) in the 'A' position even though it can be rotated to the manual f-stops.

The spring-loaded contact should retract below the surface of the lens base when NOT in the 'A' mode and extend to make contact with the one-of-a-kind A-contact on the body when in the "A" position. If it doesn't retract, the body will always see the lens in the "A" mode even when the lens has manual f-stops selected.

If the spring-loaded contact is stiff or stuck in the extended position, a drop of lighter fluid/naptha may free it for normal operation.

If you should need older camera manuals, they're available here:

Pentax camera instruction manuals, Pentax professional instruction manuals

It's good to see someone using the old P-body.

01-05-2012, 07:42 PM   #4
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Original Poster

Thank you very much for pointing me in the right direction. I just checked and in fact the A contact does not retract when the ring is moved out of "A" position. It is not stuck. It has spring resistance but never retracts. That explains why it works fine with the DSLR and with the PROGRAM modes in the film bodies but not in manual mode. I compared with the A50 f2 which works perfectly fine.


01-05-2012, 09:04 PM - 1 Like   #5
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QuoteOriginally posted by ismaelg:
It has spring resistance but never retracts.
That lens has a habit of collecting debris in the area of the aperture ring. It's possible that a simple cleaning and adjustment accessed through the rear mount would return it to full function -- although if used in the A-mode only it may not be a problem.

There's an article for disassembling that lens in the PF Articles section here:
Maintenance and Repair Articles -

Also search through member "justonedave" posts on this forum for repair tips.


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