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02-23-2015, 01:28 AM   #1
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"A" button question

Im lucky enough to have a 50mm f1.7 A series lens. Its a cracking lens and has served me well over the years. However, getting any camera to recognise that the lens is in "A" mode has always been a bit hit and miss.

Its done it on my P50, Super A and now K50. It will work with a bit of wiggling of the lens, but can anyone offer a more reliable solution? The pin protrudes where it should on the mount and retracts when its taken out of "A".

Im wondering whether squirting a little electrical contact cleaner around the area may help. (Obviously I'll be careful, as I dont want it going on or in the optics), perhaps I could wipe the lens mount to make sure its clean?

Your thoughts please.

Many thanks

02-23-2015, 01:50 AM   #2
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QuoteOriginally posted by bigyinn Quote
I could wipe the lens mount to make sure its clean?
This! Use some cotton buds and some alcohol - give it good wipe several times, then wipe dry - it would start working as new. The only problem with A contacts might occur if there is something wrong with A connection in the mechanisms of aperture that's engaging the pins - but I have never seen that happens to any of my several A lenses.

Good luck!
02-23-2015, 03:54 AM   #3
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I'll give that a try tonight, nothing to lose. I guess IPA (IsoPropyl Alcohol) will be ok to use?
02-23-2015, 04:59 AM   #4
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QuoteOriginally posted by bigyinn Quote
I'll give that a try tonight, nothing to lose. I guess IPA (IsoPropyl Alcohol) will be ok to use?
Should be - I personally always clean contacts with 70% hand sanitiser - it has gel-like form and so doesn't spill nor gets deep inside - just cleans the surface.
But I guess the IPA should do the trick - just use little. Let us know how it worked out for you

02-23-2015, 05:00 AM   #5
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if cotton buds and normal alcohol don't work probably you have problems with internal lens contacts, and need to open the lens....
for this similar problem in a sigma mini wide I circuited 'A' pin with the metal parts that make contact with the camera in internal circuit; now camera read the values of aperture correctly...
doing so I always have 'A' mode setted...

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/272338-sigm...-problems.html

good luck!
02-23-2015, 06:45 AM   #6
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QuoteOriginally posted by bigyinn Quote
I'll give that a try tonight, nothing to lose. I guess IPA (IsoPropyl Alcohol) will be ok to use?
Isopropanol will work much better than India Pale Ale (IPA).
02-23-2015, 07:54 AM   #7
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Doesn't taste as nice though!
02-23-2015, 08:24 AM - 1 Like   #8
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The aperture ring on Pentax-A SMC 50mm f/1.7 tends to give problems due to a design flaw. If you are not the 1st owner of the lens it may have been repaired and grease was used on the "A" pin internal mechanism. If this is the case, the pin will have to be disassembled and cleaned. This can be done carefully without removing the aperture ring itself (and risk losing the small ball bearing). A JIS screwdriver, fine tweezers and some lighter fluid is all that is required. Along with a reasonable amount of manual dexterity and infinite patience.

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/88051-pen...ng-repair.html

02-23-2015, 02:25 PM   #9
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Sucess!!!

Thank you so much Not a Number for pointing me to the guide.

It has helped me resolve an issue I've had with this lens for 18 years! It was always very intermittant whether it would work in A., on any of my cameras.

It turns out that I was missing the angled plate that sat underneath the sprung pin that formed the A-M Selecting plate assembly.

Through trial and error I made a replacement out of one leg of a paper binder as it was about the right width and thickness of metal. Took me a couple of hours to stop it interfering with the aperture workings and get it just so. I think it contacts the inside of the lens mount, so it completes the circuit.
Plus I lot the spring and pin a couple of times, so spent a while trying to locate it on the carpet!

Now I can use it on my new K50 with confidence!

Thanks again!
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