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09-26-2013, 06:45 AM   #1
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Pentax A 501.4 pin not recognized by k-5

I have recently acquired a nice Pentax-A 50f1.4 lens. The "A" pin is actually recessed below the mounting plate so when mounted on my k-5, it does not recognize it as "A" lens. Is this something that I can easily fix or should I send it Eric to have it fixed. Thanks in advance for your help...

09-26-2013, 06:57 AM - 1 Like   #2
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QuoteOriginally posted by aleonx3 Quote
"...A" pin is actually recessed below the mounting plate...
sounds like the tiny spring under it is missing?
09-26-2013, 07:46 AM   #3
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QuoteOriginally posted by MysteryOnion Quote
sounds like the tiny spring under it is missing?
@MysteryOnion, is this easy to find out...or is this too risky. Thanks...
09-26-2013, 07:47 AM   #4
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Is this when the aperture ring is set to "A"?

09-26-2013, 08:02 AM   #5
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QuoteOriginally posted by Not a Number Quote
Is this when the aperture ring is set to "A"?
Yes... when the ring is set to "A"; also when the camera is turned on, it asks to input the focal length...
09-26-2013, 08:33 AM   #6
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QuoteOriginally posted by aleonx3 Quote
also when the camera is turned on, it asks to input the focal length...
It will do that anyway, even with the pin in place, so that's normal.

Can't help you with the pin, though, sorry.
09-26-2013, 09:17 AM - 1 Like   #7
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QuoteOriginally posted by aleonx3 Quote
Yes... when the ring is set to "A"; also when the camera is turned on, it asks to input the focal length...
As suggested earlier perhaps the spring is missing or things are a bit gummed up. Try moistening a cotton swab with a little rubbing alcohol or lighter fluid and dab a tiny amount on the pin and jiggle the ring while depressing the "A" button. You only want a little amount as you don't want the fluid flowing into the rest of the works.

Perhaps a previous owner disassembled the lens for one reason or another and lost the spring or incorrectly re-assembled it. Does the aperture ring click-stop when off the "A" lock? The little dented ball bearing is the most commonly lost part.

Last edited by Not a Number; 09-26-2013 at 01:11 PM. Reason: spelling
09-26-2013, 09:28 AM   #8
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QuoteOriginally posted by Not a Number Quote
As suggested earlier perhaps the spring is missing or things are a bit gummed up. Try moistening a cotton swap with a little rubbing alcohol or lighter fluid and dab a tiny amount on the pin and jiggle the ring while depressing the "A" button. You only want a little amount as you don't want the fluid flowing into the rest of the works.

Perhaps a previous owner disassembled the lens for one reason or another and lost the spring or incorrectly re-assembled it. Does the aperture ring click-stop when off the "A" lock? The little dented ball bearing is the most commonly lost part.
Thanks for the suggestion with lighter fluid or rubbing alcohol, I will try that before taking it apart. The previous owner had this lens on the K1000 camera (may be the spring get stuck a little as there is no A contact on the k1000). On the whole, the lens looks in very good condition. The aperture ring works perfect with clicks and proper closer of the aperture blades.

I have another A 50f2.0 in similar situation, may be I will try to take apart that one first.

09-26-2013, 01:25 PM   #9
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If the design is similar to the f/1.7 then you should be able to remove the pin assembly without removing (and risk losing the ball bearing) the aperture ring. It might just need a bit of grease in there. On my f/1.7 this assembly is four pieces: a plate that rests on the camera, a sort of clip, small spring and the pin itself. The pin, clip and spring are so tiny it is a major pain re-assembling them if they fall apart. Which they do easily when removed from the lens.

Refer to the photos in this thread:
https://www.pentaxforums.com/forums/maintenance-repair-articles/88051-pentax-...ng-repair.html

I am in the process of reassembling my f/1.7 having done this repair. I'm waiting for the dental acrylic to cure that I needed to patch one of the screw holes when the threads stripped out (not drilled deep enough). I'm going to try holding in the ball bearing with a bit of sticky cellophane tape and a strip of paper over the two clips. These can be pulled out after the ring is in place. It might make things simpler.
09-26-2013, 06:17 PM   #10
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On my A 1.4 there is a little button that you have to push on the aperture ring to get it to lock into A position. Push and turn. If it is locked properly the aperture ring doesn't turn.
09-26-2013, 06:24 PM   #11
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QuoteOriginally posted by Not a Number Quote
If the design is similar to the f/1.7 then you should be able to remove the pin assembly without removing (and risk losing the ball bearing) the aperture ring. It might just need a bit of grease in there. On my f/1.7 this assembly is four pieces: a plate that rests on the camera, a sort of clip, small spring and the pin itself. The pin, clip and spring are so tiny it is a major pain re-assembling them if they fall apart. Which they do easily when removed from the lens.

Refer to the photos in this thread:
https://www.pentaxforums.com/forums/maintenance-repair-articles/88051-pentax-...ng-repair.html

I am in the process of reassembling my f/1.7 having done this repair. I'm waiting for the dental acrylic to cure that I needed to patch one of the screw holes when the threads stripped out (not drilled deep enough). I'm going to try holding in the ball bearing with a bit of sticky cellophane tape and a strip of paper over the two clips. These can be pulled out after the ring is in place. It might make things simpler.
Thanks, I will take a closer look at that. I also have the A 50f1.7 and 50f2.0. I noticed that they are slightly different once I opened it up. Likewise for the A50f1.4. I need to carefully plan out what to do first...
09-26-2013, 06:27 PM   #12
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QuoteOriginally posted by derekkite Quote
On my A 1.4 there is a little button that you have to push on the aperture ring to get it to lock into A position. Push and turn. If it is locked properly the aperture ring doesn't turn.
Yes.. thanks, I confirm that on the other lenses as well as the A50f1.4. The only thing is: once the Aperture is set to the 'A' position, the A pin on the lens mount should be up slightly (it happens on the other lenses), but on this A50f1.4, it stays flush to the mount. So, apparently the A assemble spring is either missing or non-functioning.
09-26-2013, 06:46 PM   #13
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Jiggle it about a bit before opening the lens up.

The pin is an absolute arse to work with, and to seat correctly again when re-assembling.
If you can avoid having to touch it, do so. (I opened up a 28mm A lens, the pin and spring took me about 5 hours to correctly re-seat. (It's a poor design)




Just try repeatedly moving from A to F22 at the same time as pressing on the A contact pin with a fingertip or a wooden toothpick (won't mark it like metal)
That fixed the issue of my 50mm1.7.

If that doesn't work, then try the cotton bud with cleaner on it.

Last edited by Blue; 10-07-2013 at 12:36 PM.
09-27-2013, 09:49 AM   #14
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I finally succeeded to reseat the spring in the A pin. Now, it works the same way as it should. I am quite surprised that it allows me to step up the aperture from 1.4, 1.6 and 1.8, 2.0 increment, which is great!! I spent many hours trying different things, the spring and pin-cap was so tiny that it is difficult to handle. I also lost a few springs (thanks to the warnings but still do), I sabotaged a broken FA28-70 f4 lens to salvage extra springs.

Thanks to everyone on this thread for all the suggestions, they were all very helpful indeed and let me focus on the part to be fixed.

I suppose we can close this thread now..
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