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06-01-2021, 11:19 AM   #1
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Underexposure problem, maybe aperture solenoid, maybe not

I'm having a problem with my Pentax K-50 that I've seen several earlier threads on, but the symptoms are not quite the same. Pictures taken through the viewfinder are very underexposed, while in live view they are normal. According to earlier threads, it looks very much like the aperture control solenoid not working, especially as in manual mode the pictures I get are independent of the aperture setting. I tried the trick of assigning Optical Preview to the RAW/Fx button and clicking it a lot to exercise the mechanical parts. On the widest aperture setting, nothing happens when I press the button (as I would expect), but on all other aperture settings, pressing the button stops it right down. This looks more like a problem in how the camera is controlling the aperture than a simple failure of the solenoid.

There is a further complication. If I fit a lens with its own aperture ring and set the aperture there, there is still a problem. The camera shows the F number as F--, so it knows that aperture adjustment is not available. The aperture mechanism shouldn't then be an issue. But the same thing still happens. In automatic mode, if I switch between viewfinder and live view, then even without taking a picture I can see the exposure and ISO settings changing between the two. If I rotate the aperture ring in live view mode, I can see the ISO changing to compensate. In viewfinder mode, the ISO and exposure time remain fixed.

This happens whether the metering mode is set to multi-segment, center-weighted, or spot.

I have updated the camera firmware (from 1.00 to 1.10) but nothing changed.

06-01-2021, 11:25 AM   #2
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This may help with the F-- issue.
Using Manual Lenses (M42 Screwmount, M , K) on Pentax DSLRs F-- - PentaxForums.com
06-01-2021, 02:25 PM   #3
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Welcome to the forum! Nice to have you with us.
06-01-2021, 03:10 PM   #4
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When I read your original post, it seems as though you have tried lenses both with and without aperture rings, is that correct? Can you be more specific about which lenses you tried.

Also, what setting is the mode dial in, and what are your other settings?

Post an image here with EXIF intact and we may be able to spot the setting that's giving you trouble.

If all else fails, do a complete factory reset on your camera, and see if that fixes it. I'd also try cleaning all the lens and camera contacts with an alcohol wipe since this is a common source of problems.

06-01-2021, 03:59 PM   #5
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same with my K-30

QuoteOriginally posted by Raak Quote
I'm having a problem with my Pentax K-50 that I've seen several earlier threads on, but the symptoms are not quite the same. Pictures taken through the viewfinder are very underexposed, while in live view they are normal. According to earlier threads, it looks very much like the aperture control solenoid not working, especially as in manual mode the pictures I get are independent of the aperture setting. I tried the trick of assigning Optical Preview to the RAW/Fx button and clicking it a lot to exercise the mechanical parts. On the widest aperture setting, nothing happens when I press the button (as I would expect), but on all other aperture settings, pressing the button stops it right down. This looks more like a problem in how the camera is controlling the aperture than a simple failure of the solenoid.

There is a further complication. If I fit a lens with its own aperture ring and set the aperture there, there is still a problem. The camera shows the F number as F--, so it knows that aperture adjustment is not available. The aperture mechanism shouldn't then be an issue. But the same thing still happens. In automatic mode, if I switch between viewfinder and live view, then even without taking a picture I can see the exposure and ISO settings changing between the two. If I rotate the aperture ring in live view mode, I can see the ISO changing to compensate. In viewfinder mode, the ISO and exposure time remain fixed.

This happens whether the metering mode is set to multi-segment, center-weighted, or spot.

I have updated the camera firmware (from 1.00 to 1.10) but nothing changed.
Yes , it is a "normal" behaviour in the early stage of solenoid failure.
My K-30 is doing more less the same things.
06-01-2021, 05:10 PM   #6
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QuoteOriginally posted by Raak Quote
I'm having a problem with my Pentax K-50 that I've seen several earlier threads on, but the symptoms are not quite the same. Pictures taken through the viewfinder are very underexposed, while in live view they are normal. According to earlier threads, it looks very much like the aperture control solenoid not working, especially as in manual mode the pictures I get are independent of the aperture setting. I tried the trick of assigning Optical Preview to the RAW/Fx button and clicking it a lot to exercise the mechanical parts. On the widest aperture setting, nothing happens when I press the button (as I would expect), but on all other aperture settings, pressing the button stops it right down. This looks more like a problem in how the camera is controlling the aperture than a simple failure of the solenoid.

There is a further complication. If I fit a lens with its own aperture ring and set the aperture there, there is still a problem. The camera shows the F number as F--, so it knows that aperture adjustment is not available. The aperture mechanism shouldn't then be an issue. But the same thing still happens. In automatic mode, if I switch between viewfinder and live view, then even without taking a picture I can see the exposure and ISO settings changing between the two. If I rotate the aperture ring in live view mode, I can see the ISO changing to compensate. In viewfinder mode, the ISO and exposure time remain fixed.

This happens whether the metering mode is set to multi-segment, center-weighted, or spot.

I have updated the camera firmware (from 1.00 to 1.10) but nothing changed.
Unfortunately the solenoid is a key part of the aperture block and it does sound as if the aperture block is failing. Your further complication sounds normal with the "F" displayed, check the section in your manual on "using the aperture ring". There are some variances depending on the lens used, but I think manual mode should work.
06-01-2021, 10:23 PM - 1 Like   #7
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QuoteOriginally posted by Raak Quote
I'm having a problem with my Pentax K-50 that I've seen several earlier threads on, but the symptoms are not quite the same. Pictures taken through the viewfinder are very underexposed, while in live view they are normal.
Actually those symptoms are exactly the same, just not everybody uses LiveView and thus won't notice "if the Pentax works in LV-mode".

QuoteOriginally posted by Raak Quote
According to earlier threads, it looks very much like the aperture control solenoid not working, especially as in manual mode the pictures I get are independent of the aperture setting
That is so, im M-Mode the solenoid is not in function!
But you missed the most imporant threads


QuoteOriginally posted by Raak Quote
I tried the trick of assigning Optical Preview to the RAW/Fx button and clicking it a lot to exercise the mechanical parts. On the widest aperture setting, nothing happens when I press the button (as I would expect), but on all other aperture settings, pressing the button stops it right down. This looks more like a problem in how the camera is controlling the aperture than a simple failure of the solenoid.
No, this is typical failure of just the solenoid!


QuoteOriginally posted by Raak Quote
There is a further complication. If I fit a lens with its own aperture ring and set the aperture there, there is still a problem. The camera shows the F number as F--, so it knows that aperture adjustment is not available.
In 99,95 of all cases that means that your Pentax isn't set for manual lenses in the menu.
As @ramseyebuckeye wrote already.


QuoteOriginally posted by Raak Quote
The aperture mechanism shouldn't then be an issue
For 99% it is THE ISSUE!

QuoteOriginally posted by Raak Quote
But the same thing still happens. In automatic mode, if I switch between viewfinder and live view, then even without taking a picture I can see the exposure and ISO settings changing between the two. If I rotate the aperture ring in live view mode, I can see the ISO changing to compensate. In viewfinder mode, the ISO and exposure time remain fixed.
Very normal behaviour with ABF.

You tried to find out a lot but didn't read those guidelines how to detect ABF:
Detection of aperture block/diaphragm-block failure/stuck solenoid K-30, K-50, K500 - PentaxForums.com
Then you know for sure.

06-04-2021, 01:53 AM   #8
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Thanks for that link to tests for ABF.

By the first test (take a picture using the viewfinder in AV mode with the widest and the narrowest aperture), the wide setting gives an underexposed image and the narrowest gives a correctly exposed one. Looks like ("99.9%") the solenoid is stuck and needs to be replaced.

But by the second test (look into the lens while switching Live View on and off), I'm not sure how to interpret the result. The aperture does switch between closed and open, but it is at maximum in viewfinder view and minimum in live view. This is so independently of the F stop selected on the camera (in Av mode).

So the diaphragm is being operated, but only at two settings, maximum and minimum.

As for the use of an aperture ring, the camera is already set to allow this ("Using Aperture Ring" -> Enable). It takes pictures whether the ring is on "A" or any manual setting. I had assumed that the reason the camera shows "F--" when aperture is set on the aperture ring is that my lenses with aperture rings aren't modern enough to communicate their setting to the camera. The K-50 and the lens that came with it (no ap ring) are 15 years old, and my Ricoh 28-85mm lens (with ring) at least ten years older than that.
06-05-2021, 12:15 AM   #9
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QuoteOriginally posted by Raak Quote
By the first test (take a picture using the viewfinder in AV mode with the widest and the narrowest aperture), the wide setting gives an underexposed image and the narrowest gives a correctly exposed one. Looks like ("99.9%") the solenoid is stuck and needs to be replaced.
That already is enough to know that the solenoid is stuck!
QuoteOriginally posted by Raak Quote
But by the second test (look into the lens while switching Live View on and off), I'm not sure how to interpret the result. The aperture does switch between closed and open, but it is at maximum in viewfinder view and minimum in live view. This is so independently of the F stop selected on the camera (in Av mode).
So the diaphragm is being operated, but only at two settings, maximum and minimum.
That's correct as well for a stuck solenoid!

Solenoid functioning correct: The diaphragm goes from wide open to f4,0
Solenoid stuck: The diaphragm goes from wide open to f22 or f32, whatever your lens with A-ring has as max. closed aperture.

And yet it seems as if the Pentax takes correct photos in LV. It seems only and is usually only in the beginning, after a while it is full stuck there as well. The reason I have described already.
When checking EXIF, one can tell something is not quite alright, because metering was with f22 or f32 instead of f4,0.

QuoteOriginally posted by Raak Quote
As for the use of an aperture ring, the camera is already set to allow this ("Using Aperture Ring" -> Enable). It takes pictures whether the ring is on "A" or any manual setting. I had assumed that the reason the camera shows "F--" when aperture is set on the aperture ring is that my lenses with aperture rings aren't modern enough to communicate their setting to the camera. The K-50 and the lens that came with it (no ap ring) are 15 years old, and my Ricoh 28-85mm lens (with ring) at least ten years older than that.
The Pentax shows "F--" but the "--" will not blink if the aperture-ring is enabled.
Select aperture on the ring
Focusing

Green button
Release

The "--" after the F will blink if "Using Aperture Ring" is disabled.

But a A-Lens will automatically give data, so it will show F1,7 or F5,6... whatever in AV-mode is set.

AV-mode will not work with lenses without A-ring except Takumar M42 lenses and similar with M/Auto-switch, but the time needed is the same:
Select aperture - focus - press Release - Press Release again
And yet: Green button metering is better, more precise.

But this is material for another thread!

Here we are interested only for the solenoid and ABF!

Last edited by photogem; 06-05-2021 at 12:37 AM.
06-05-2021, 09:46 AM   #10
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QuoteOriginally posted by photogem Quote
That already is enough to know that the solenoid is stuck!

That's correct as well for a stuck solenoid!

Solenoid functioning correct: The diaphragm goes from wide open to f4,0
Solenoid stuck: The diaphragm goes from wide open to f22 or f32, whatever your lens with A-ring has as max. closed aperture.

And yet it seems as if the Pentax takes correct photos in LV. It seems only and is usually only in the beginning, after a while it is full stuck there as well. The reason I have described already.
When checking EXIF, one can tell something is not quite alright, because metering was with f22 or f32 instead of f4,0.


The Pentax shows "F--" but the "--" will not blink if the aperture-ring is enabled.
Select aperture on the ring
Focusing

Green button
Release

The "--" after the F will blink if "Using Aperture Ring" is disabled.

But a A-Lens will automatically give data, so it will show F1,7 or F5,6... whatever in AV-mode is set.

AV-mode will not work with lenses without A-ring except Takumar M42 lenses and similar with M/Auto-switch, but the time needed is the same:
Select aperture - focus - press Release - Press Release again
And yet: Green button metering is better, more precise.

But this is material for another thread!

Here we are interested only for the solenoid and ABF!
Can you explain the exact role of the aperture solenoid? The solenoid seems to be a purely on/off device, but the camera is able to set the aperture to many different settings. What accomplishes that?

Anyway, I've watched a bunch of Youtube videos on getting at the solenoid, and your articles on on the whole history of this, and why filing the moving part isn't a good idea, and why only the "white" solenoid is good enough. There are people selling the white solenoid on eBay (or at least claiming to, eBay being eBay), so hopefully I'll be able to fix this at some point.
06-05-2021, 12:14 PM   #11
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QuoteOriginally posted by Raak Quote
Can you explain the exact role of the aperture solenoid? The solenoid seems to be a purely on/off device, but the camera is able to set the aperture to many different settings. What accomplishes that?

Anyway, I've watched a bunch of Youtube videos on getting at the solenoid, and your articles on on the whole history of this, and why filing the moving part isn't a good idea, and why only the "white" solenoid is good enough. There are people selling the white solenoid on eBay (or at least claiming to, eBay being eBay), so hopefully I'll be able to fix this at some point.
The lens is fully open as you frame the photo, then shuts down to the value set when you take the photo - shutting down is stopped by the body if aperture is set by the body but is stopped by the lens if aperture is set by the aperture ring.

The solenoid stops the shutting down if the body has set the aperture.

So if you have a lens where f/4 is the widest opening and f/22 is the narrowest opening - and the aperture is set at f/5.6, a correctly working solenoid will stop shutting down at f/5.6 {just a little smaller than the f/4 opening}, but it will go all the way to f/22 {a very small opening} if the solenoid is not working correctly. So, you need to set the fstop to the next smallest opening to the largest opening in order to test it.

When my K-30 began to show symptoms of what I call "Dark Image Syndrome", I began carrying a FA 28-105mm lens with me, because it does have an aperture ring, and when I could no longer get the body to reliably control the aperture, I simply began to use it.

Last edited by reh321; 06-05-2021 at 12:21 PM.
06-05-2021, 01:46 PM   #12
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QuoteOriginally posted by Raak Quote
Can you explain the exact role of the aperture solenoid? The solenoid seems to be a purely on/off device, but the camera is able to set the aperture to many different settings. What accomplishes that?
Take a lens off camera and change the aperture setting. You will notice 2 things. The aperture closes down or opens up. The aperture lever moves corespondingly.
It effectively changes the minimum aperture. So instead of having f/22 or f/32 you only have what you set. The solenoid is giving all or nothing but you mechanically limit that range by changing the aperture ring.

Edit. Yeah thats the opposite part you asked about. Opps.
The solenoid has to allow the camera to limit the the aperture lever. It must be when it opens it releases the blocking device.

So is aperture block a verb as in the blocking or in a physical thing like the engine block of a car?

Last edited by swanlefitte; 06-05-2021 at 01:56 PM.
06-05-2021, 10:35 PM   #13
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QuoteOriginally posted by Raak Quote
Can you explain the exact role of the aperture solenoid? The solenoid seems to be a purely on/off device, but the camera is able to set the aperture to many different settings. What accomplishes that?
Dark exposure problems on K-30 or K-50? Discussion Thread - Page 20 - PentaxForums.com


QuoteOriginally posted by Raak Quote
Anyway, I've watched a bunch of Youtube videos on getting at the solenoid, and your articles on on the whole history of this, and why filing the moving part isn't a good idea, and why only the "white" solenoid is good enough. There are people selling the white solenoid on eBay (or at least claiming to, eBay being eBay), so hopefully I'll be able to fix this at some point.
As far as I know there is only one seller on ebay.com (USA) selling the white solenoid:
Pentax K-30 K-50 K-70 K-S1/S2 K-500 Genuine White Solenoid Part - Japan - | eBay
His offers are fine.
I don't know about the offers on ebay.uk... to new to know.
06-06-2021, 01:06 AM - 1 Like   #14
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QuoteOriginally posted by Raak Quote
Anyway, I've watched a bunch of Youtube videos on getting at the solenoid, and your articles on on the whole history of this, and why filing the moving part isn't a good idea, and why only the "white" solenoid is good enough. There are people selling the white solenoid on eBay (or at least claiming to, eBay being eBay), so hopefully I'll be able to fix this at some point.
I'm in the UK, and I've self-repaired a K50. I didn't find any, apparently genuine, local sellers of "white" solenoids on Ebay UK. I decided to keep an eye on Ebay for non-working, old, or just cheapish Pentax cameras of the models listed by Photogem. I checked the descriptions carefully to try to make sure any problems were not likely to be solenoid related. It was not long before a couple of cameras were listed and bought for 20/30(I also have a K30 which may need a solenoid replacement at some point). A plus to doing this is that you get an idea of the work necessary by extracting the solenoid from what is basically then a scrap body.

Transplant went well and K50 all good.

Colin
07-04-2021, 11:13 AM - 2 Likes   #15
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The replacement solenoid arrived yesterday, and I fitted it today. I got it from the seller that photogem recommended -- his listing shows up on ebay uk as well. The surgery went well and the K50 is back in working order. The soldering is a bit of a trial! Many thanks to photogem for his advice and extensive documentation on exactly how to do the operation.
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