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10-01-2022, 09:18 AM   #1
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Confirm aperture block failure in K-70

Wondering if someone can help me determine if my 5 year old Pentax K-70 does in fact have the aperture block failure.

When I use the standard lens that came with it (DA 18-135) the pictures are OK if taken in LV mode but dark when using the viewfinder.

However, when using my other Pentax lens (HD PENTAX DA 55-300mm F4 5.8 ED WR) the images are OK in either mode.

Just looking for confirmation if this is the dreaded "aperture block failure" I've been reading about. Since this is within the camera I would think it would affect either lens.

See sample pics below: dark one using viewfinder and bright one using LV

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PENTAX K-70  Photo 
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PENTAX K-70  Photo 
10-01-2022, 10:37 AM   #2
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Could be but not entirerly clear from those examples. With aperture block failure the image is usually really dark, because the lens iris remains closed - F22. Your image exif says f8 so thats 3 stops : yeah could be 3 stops under but ...
Try setting the lens to min F wide open.
Certainly in its early stages this can be inconsistent and intermittent in its occurence (but gets worse and persistent) - I set the RAW/Fx button on my KS2 to stop down preview and a couple of presses of that would free up the solenoid allowing me to keep using it for a while longer. But thats not a fix or particularly recommended.
Have a look at teh relevant thread here:

How to detect aperture-block failure/stuck solenoid on Pentax K-70 - PentaxForums.com
10-01-2022, 11:21 AM   #3
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I checked out the link but I'm still not sure if it's the aperture block issue.
As per the instructions, Method 1 outcome is exactly as described (in Av mode @ F3.5 the image is dark while @ F22 the image is bright)
Using Method 2, looking into the lens and going into Live View mode I can see the aperture move correctly (which I assume means the solenoid is working)
10-01-2022, 11:44 AM   #4
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If you get dark exposures only with the DA 18-135mm lens, but get consistently good exposures with your other lens(es), then the problem is most likely with the lens, not the camera. I presume your second example was taken with LV, so that would indicate not a lens problem. But then it could be intermittent.

Why not shoot some more with the other lenses to see how it goes? With such a limited number of results, hard to say for sure there is not an intermittent problem with lens blades or contacts. If the problem only arises with the DA 18-135mm, and not at all with another lens, that should bring more suspicion upon the lens.


Last edited by mikesbike; 10-01-2022 at 11:52 AM.
10-01-2022, 01:58 PM - 1 Like   #5
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At the beginning of aperture block failure, it will come and go and work better in live view. It can go away and come back so the fact it wasn't with one lens could just be timing.

However your two shots are totally different.
shot 1 : 1/100 f/8 iso 400 and shot 2 1/60 f/4 iso 3200. You should expect shot 2 is about 3 stops brighter from iso, a stop brighter from aperture stop, and about 2/3rd bright from the shutter speed for a total 4 2/3rd stops brighter.
10-01-2022, 02:23 PM - 1 Like   #6
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Hi Jonh,

The shots you show are very much like the ones I got at the beginning of the aperture block happening on my K-70. Your PLM will not be affected by the aperture block however other lenses will that's why it works fine it doesn't need the solenoid in the same way.

At the start if you use burst mode with the 18-135mm then it might unblock mine did but had to keep doing it every time I switched it on.

I got a lot of info from this thread

New K-70 and Aperture Block

New K-70 and Aperture Block - PentaxForums.com
10-01-2022, 04:28 PM   #7
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Thanks for the info.
The burst mode did in fact unblock it and it works normally for a period of time.
If I shut off the camera and leave it for 10 min the problem returns but can again be fixed using the burst method.

But I guess this is pretty conclusive that this is the aperture block problem.

Curious that this issue is present only in my 18-135mm lens. The other zoom lens does not exhibit any problems (at least not yet).


Last edited by jonh; 10-01-2022 at 04:44 PM.
10-01-2022, 05:13 PM - 1 Like   #8
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QuoteOriginally posted by jonh Quote
Curious that this issue is present only in my 18-135mm lens. The other zoom lens does not exhibit any problems (at least not yet)
Is the 55-300 the PLM version. If it is then it's not curious the 55-300 plm will still work perfectly fine as it doesn't use the Solenoid. I used that lens pretty much exclusively for
2 or 3 months which I suspect caused the issue as the solenoid is more likely to fails if not exercised.
10-01-2022, 08:23 PM   #9
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QuoteOriginally posted by jonh Quote

However, when using my other Pentax lens (HD PENTAX DA 55-300mm F4 5.8 ED WR) the images are OK in either mode.
If this is the specific 55-300, Iím lost. If it was the PLM version it would make sense. Is the aperture lever on the 18-135 smooth and freely operating if you have the lens off the camera?
10-02-2022, 06:07 AM   #10
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QuoteOriginally posted by jonh Quote
QuoteOriginally posted by luckylu Quote
At the start if you use burst mode with the 18-135mm then it might unblock mine did but had to keep doing it every time I switched it on.
The burst mode did in fact unblock it and it works normally for a period of time.
If I shut off the camera and leave it for 10 min the problem returns but can again be fixed using the burst method.
Burst mode is not a good idea! You can do further damage!
I don't know which cobblers somewhere on the www do still recommend such really a silly practice!!! (not you both, you just got it from somewhere else!)
QuoteOriginally posted by jonh Quote
But I guess this is pretty conclusive that this is the aperture block problem.

Curious that this issue is present only in my 18-135mm lens. The other zoom lens does not exhibit any problems (at least not yet).
I'd say it is pretty sure ABF or better the beginning (and usually it rapidly develops stronger).

As others mentioned, if your 55-300 is the latest PLM version, this lens is not affected!
QuoteOriginally posted by jonh Quote
I checked out the link but I'm still not sure if it's the aperture block issue.
As per the instructions, Method 1 outcome is exactly as described (in Av mode @ F3.5 the image is dark while @ F22 the image is bright)
Then it is ABF for sure!
The only test you need!
If applied as you did and wide open = dark and full closed = alright it is for 99,99% ABF
If something with the lever of the lens would be wrong, one would NOT get those symptoms.


QuoteOriginally posted by jonh Quote
Using Method 2, looking into the lens and going into Live View mode I can see the aperture move correctly (which I assume means the solenoid is working)
Yes, and that happens often at the beginning. The solenoid gets an extra surge of power due to the way LV works.
It is all explained here:
https://www.pentaxforums.com/forums/53-pentax-dslr-camera-articles/389194-li...x-cameras.html

And then, apply:

Tutorial/Repair Pentax K-70 with aperture-problem: Exchange solenoid - PentaxForums.com

Last edited by photogem; 10-02-2022 at 06:13 AM.
10-02-2022, 02:22 PM   #11
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QuoteOriginally posted by luckylu Quote
Is the 55-300 the PLM version. If it is then it's not curious the 55-300 plm will still work perfectly fine as it doesn't use the Solenoid. I used that lens pretty much exclusively for
2 or 3 months which I suspect caused the issue as the solenoid is more likely to fails if not exercised.
Yes it's the PLM version so I guess it makes sense this lens works fine
10-02-2022, 06:12 PM   #12
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QuoteOriginally posted by jonh Quote
Yes it's the PLM version so I guess it makes sense this lens works fine
Ah. Your original post listed the wrong aperture range. The 55-300 with that aperture isnít the PLM. That confused me. In that case yes this is pretty likely abf.
10-03-2022, 11:50 PM   #13
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QuoteOriginally posted by jonh Quote
Yes it's the PLM version so I guess it makes sense this lens works fine
The DA55-300 ED/PLM lens ALWAYS works fine when there is ABF because it doesn't use the mechanical aperture-control but electro-magnetic aperture-control. It doesn't have an aperture-lever

This goes for all KAF-4 lenses (PLM is the motor used in this lens and has nothing to do with KAF-4)
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