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07-10-2018, 01:47 AM   #1
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My K-50 aperture or shutter problem or fix.

I'm a proud owner of a used Pentax K-50. About 1000 shots threw my camera I started getting black under exposed now what do I do?


Last edited by jonnie_webb; 07-11-2018 at 03:31 AM. Reason: looking for answers
07-10-2018, 03:42 AM   #2
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wow, that sounds like a bizarre thing, but a nice solution. I hope you'll fix this.
07-10-2018, 03:46 AM   #3
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What a great idea!

Taking the lens mount ring off the camera __might__ make the demagnetizing process more effective.
07-10-2018, 04:26 AM - 1 Like   #4
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Does your mirror lens by chance have a non-conductive mount (black vs bare metal or with pins)? Lenses with non-conducting mounts on a K-50 will cause the green button not to work properly. If the lens does not have a conductive base a quick and dirty test would be to place a bit of metal foil over the "data" pin (near 6 o'clock on the body mount) and trying the green button.

Are you experiencing dark frames when using say DA lenses without aperture rings or A, F, or FA lenses set to "A"?

Does the fixed aperture mirror lens have exposure problems in Av mode?

The aperture control failure usually occurs with fully automatic lenses where the stop down actuator does not position properly to keep the iris at the proper opening. The lens stops down completely to say f22 rather than f8. Lens with aperture rings continue to work properly with the green button because it is the ring setting that stops the iris at the set opening not the camera body. Since there fixed aperture lenses have no stop down levers on them the failure of the stop down actuator is irrelevant.

And in the past no one who has worked on the solenoid and checked has reported the parts being magnetized - i.e. the filings from horse shoe core are not magnetized. You may cause more harm than good exposing electromagnetic components of your camera to strong degaussing fields. You may even demagnetize the permanent magnet of the solenoid which will cause it to fail too.

See also:
https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/315725-dark-exposur...-me-first.html


Last edited by Not a Number; 07-10-2018 at 04:41 AM. Reason: reorganization, add link
07-10-2018, 10:58 AM   #5
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So the aperture control block also controls the shutter but I thought symptoms were failure to operate the shutter eventually not dark frames with fixed aperture lenses. Perhaps post some full exif intact links or pictures to show us what the mirror lens exposures were. Maybe use a smartphone app or just sunny 16 to calculate an appropriate exposure and try M mode on a few also. It's not as accurate as TTL but it works.
07-10-2018, 01:50 PM   #6
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QuoteOriginally posted by Not a Number Quote
Does your mirror lens by chance have a non-conductive mount (black vs bare metal or with pins)? Lenses with non-conducting mounts on a K-50 will cause the green button not to work properly. If the lens does not have a conductive base a quick and dirty test would be to place a bit of metal foil over the "data" pin (near 6 o'clock on the body mount) and trying the green button.

Are you experiencing dark frames when using say DA lenses without aperture rings or A, F, or FA lenses set to "A"?

Does the fixed aperture mirror lens have exposure problems in Av mode?

The aperture control failure usually occurs with fully automatic lenses where the stop down actuator does not position properly to keep the iris at the proper opening. The lens stops down completely to say f22 rather than f8. Lens with aperture rings continue to work properly with the green button because it is the ring setting that stops the iris at the set opening not the camera body.
The problem with the solenoid always happens with "auto" lenses, or with lenses set to "A", because the solenoid is part of the unit that enables the body to control the aperture. Any problem with a fixed-aperture lens must have a different cause.
07-10-2018, 06:29 PM   #7
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I had (and may have in the future) what sounds like a similar problem with my K-30, You might take the steps listed at the following link and see if they help: my fix of the K-30 aperture problem without disassembly: Pentax SLR Talk Forum: Digital Photography Review. Who wants to pay $200 to have a camera repaired when it probably isn't worth $200? On the other hand, one doesn't like to see what otherwise is a good unit put out to pasture. Good luck.
07-10-2018, 08:03 PM - 1 Like   #8
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QuoteOriginally posted by reh321 Quote
The problem with the solenoid always happens with "auto" lenses, or with lenses set to "A", because the solenoid is part of the unit that enables the body to control the aperture. Any problem with a fixed-aperture lens must have a different cause.
In the lower end bodies like the K-50 the solenoid is also involved in the mirror and shutter and can eventually fail entirely. While it is atypical behavior for a fixed aperture lens to have problems it isn't entirely impossible. (At least that is what I recall but I cannot find sources right now - too tired near bedtime.)

07-10-2018, 08:57 PM   #9
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QuoteOriginally posted by jonnie_webb Quote
I'm a proud owner of a used Pentax K-50. About 1000 shots threw my camera I started getting black under exposed
Seven hours after first posting, you made an edit of your Original Post. I never saw it before you edited it, and it makes no sense now. My words in this thread have all been reactions to what others are saying.It would help if you would restate the problem.
07-10-2018, 09:02 PM   #10
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QuoteOriginally posted by jwcjrccc Quote
I had (and may have in the future) what sounds like a similar problem with my K-30, You might take the steps listed at the following link and see if they help: my fix of the K-30 aperture problem without disassembly: Pentax SLR Talk Forum: Digital Photography Review. Who wants to pay $200 to have a camera repaired when it probably isn't worth $200? On the other hand, one doesn't like to see what otherwise is a good unit put out to pasture. Good luck.
'Optical Preview' does work well to free the solenoid under partial failure, but it would have no value under the total failure scenario postulated below
QuoteOriginally posted by UncleVanya Quote
In the lower end bodies like the K-50 the solenoid is also involved in the mirror and shutter and can eventually fail entirely. While it is atypical behavior for a fixed aperture lens to have problems it isn't entirely impossible. (At least that is what I recall but I cannot find sources right now - too tired near bedtime.)
Are you assuming that all frames are black?
07-10-2018, 09:23 PM   #11
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QuoteOriginally posted by reh321 Quote
'Optical Preview' does work well to free the solenoid under partial failure, but it would have no value under the total failure scenario postulated below
Are you assuming that all frames are black?
No - when my K-50 failed I had atypical failure. Sometimes it behaved as normal overly stopped down) but sometimes it just failed to set the right shutter speed - giving me really slow shutter speeds in bright daylight that blurred and were bright. I am only saying that until we have pictures with intact exif we don't know what's up.
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