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02-01-2019, 11:12 AM   #1
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Every shot under exposed, K-S1

I bought this camera new in April of 2017. It was on WOOT as a daily deal for $249 with lens and FLU card .. all new in the box. I never used the camera much (my Olympus Pl6 is my go to camera). The Pentax has only 300 shutter actuations. I grabbed it last week to take to the Mecum motorcycle auction and it glitched right off the bat with every shot under exposed no matter where the settings, even after a total reset.

Finally had a minute to look more closely. No change, everything underexposed. Lens aperture working nicely, camera diaphragm actuator also working as viewed with the lens off. Figuring is has to be something sticky from sitting in the mechanical diaphragm, I set the camera to the continuous shot setting and held the camera up to the light and fired away. The problem was solved after the first burst of 30 or so shots.

Whether this will help anyone else with the same malfunction .. I don't know. But I thought I'd post it just so the information is out there. No question that it was a sticky diaphragm actuator in the camera ( the lens seemed to work fine on inspection)

02-01-2019, 11:45 AM - 1 Like   #2
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Sounds like aperture block failure. There are a lot of threads devoted to the problem here.
02-01-2019, 12:23 PM   #3
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You may find diagnostic procedure here. I had similar problem with my K-S2, and as far as I know aperture block is related to age of the camera, not shutter count.
02-01-2019, 05:14 PM   #4
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The camera actuator probably is not working, it is interesting it appears to work with lens off. The above posts are your first step.
There is a diy cure and places to fix it for $100.

02-01-2019, 06:00 PM - 2 Likes   #5
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The actuator doesn't stop functioning. It always stops the lens down completely when the control assembly fails. That's why non-A lenses with aperture rings continue to work in manual mode with the green button. The aperture ring keeps the iris open at the set f-stop.
02-01-2019, 10:10 PM   #6
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Did you try Av mode at f/22 in your tests? If that exposed well it's a big clue the aperture is not opening.
02-02-2019, 04:45 AM   #7
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Diagnostic suggestions:
Dark exposure problems on K-30 or K-50? Read me first! - PentaxForums.com

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