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03-31-2021, 12:20 PM   #1
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Join Date: Sep 2010
Location: Calgary
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K50 aperture control failure

Hi Pentaxians,

My trusty K50 has recently developed a problem:
The camera control of the iris has stopped functioning, leaving the lens totally shut down to the smallest iris setting.

The camera thinks it has access to it, and shows the exposure meter happily flashing away, but the photos all come out almost black.

I can work around this for the most part, as I no longer use the plastic Zoom lens it came with, and exclusively use my film prime lenses, so I have easy access to manual iris settings.

The issue comes with my desire to use high speed flash for Summertime photography.
Even though I have a manual high speed flash unit, so the camera shouldn't need to access the iris as it has nothing to do with the exposure calculations, it still forces the camera to 1/180 flash sync speed if not using the "A" auto iris setting.

And as this then shuts the iris completely to its smallest setting, it is essentially unusable.

Can anyone tell me:

1. Is there a fix for this failure of camera iris control? Is there a repair kit / part I can buy and install to repair my K50?

2. Is there any way to tell the camera that it doesn't need to access the iris for high speed flash use, as everything (Shutter speed, ISO, focus, iris, flash power setting) is being dealt with by ME, so the camera has no reason to access the iris..?

Surely, all the camera needs to do for high speed flash sync is know the shutter speed, in order to sync the flash pulses.

As I'm manually dealing with exposure / flash pulse strength, so am not using the built in exposure meter, it has no need / reason to know what the iris is set to.
So why does it seem to insist on having access to the iris?

Any assistance on repairing my K50 and / or setting it to allow high speed flash would be greatly appreciated.

Thank you.

03-31-2021, 12:30 PM   #3
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My K-50 developed the problem about two years ago. I did the "Sand down the solenoid" method and it revived it for a while, but recently went back to being stuck, again. In addition to this, the fingers on the on-off ring switch were almost destroyed when I tried to put the camera back together, again.

I already had one lens with a manual aperture control ring, but I picked up a 10mm wide angle manual lens to round out my little "manual" collection to keep using the camera without having to replace or repair anything.

At this point, I'm just saving up to get a K-1 or K-3 II to replace it and then use it as a little backup camera if I need it.
04-05-2021, 09:31 PM   #4
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@DafTekno: It is with 99% certainty the stuck solenoid, study the threads Mark mentions and apply DIY, otherwise you can work only restricted with lenses allowing manual aperture setting

@ThomSirveaux: although the sanding sometimes works, you were lucky that no further problems came with it.
As you disassembled your K-50 already you know the procedure, so it is simple to do it right this time and get the Japan-made DSLR solenoid.

Then it is easy to fix the On/Off switch, if you buy a K100D, *ist or similar you can take that tiny part with the fingers from there, it fits.
You can see that part here, I haven't yet disassembled a KP but except the K-S1 that part is similar in all other Pentax bodies.
You can see, it is just one screw to get it off.


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