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07-17-2010, 02:52 PM   #1
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Need help - K20D forcing arperture w/manual lenses

One of my K20's has me for a loop as every manual lens I place on it ends-up wide open(no aperture control whatsoever). I can turn the dial, but the diaphragm stays open.

If I take a K 35mm lens and adjust the ring, the diaphragm works normally.
If I mount it back on(upon locking in place), it will open fully and stay there.

Has anyone seen this type of behavior before?
I'm thinking a mechanism is jammed in the mount which is forcing the lens lever down.
Though I've never had a problem like this happen before on these camera's

07-17-2010, 03:25 PM   #2
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to get the obvious cause out of the way: you do have the camera in Manual mode, right?
07-17-2010, 03:36 PM   #3
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QuoteOriginally posted by urje Quote
to get the obvious cause out of the way: you do have the camera in Manual mode, right?


Yes, all modes same result.

I think the aperture lever is stuck or defective tbh. But I can't seem to find anything wrong with it by looking.
I read in another thread that the little spring could get dislodged, but none of the images were working and so I can't really confirm this is the problem.
For me everything seems to work, except that the moment I mount a manual lens on the camera, it goes wide open and stays there.

Last edited by JohnBee; 07-17-2010 at 03:47 PM.
07-17-2010, 04:02 PM   #4
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Okay here's what I have found(so far)...

The camera stops down(using green button) and when it does the arperture closes momentarilly, but as soon as its done, it returns to being wide open. Remember... this is a manual lens(nor PK/A). So it should(normally) be in the given aperture setting on the dial.
However, it doesn't do that. It really seems as though something is pushing the lens lever when I lock the lens on the mount. I tried examining the mount but I can't see any discrepencies whatsoever in the mechanism.

I'm really stumped as to what might cause this

07-17-2010, 04:19 PM   #5
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You Do know that the DIAL, has no affect on the aperture setting on a K (or M) lens, don't you? Or are you talking about the Aperture ring? Either way, These lenses only stop down when you press the green button or when you snap the shutter. If you want to preview what is going to happen, (and meter for exposure) you can use the Optical preview (in M mode only) by pulling the power switch to the right. You have to set the camera to use it instead of Digital preview in the custom menu.

Also, you've set the camera to Allow Aperture Ring, Correct?

07-17-2010, 04:26 PM   #6
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To summarize the above:
  • Set "Using Aperture Ring"=permitted on the setup menu
  • Put camera in M mode
  • Choose aperture using ring on lens
  • Press green button to meter for shutter speed
  • Do exposure
The lens will remain wide open in all modes except M. Due to weirdness of the metering system, it may be necessary to chimp and adjust the exposure up/down. You can also use the optical preview for metering if that works better for you.



Steve
07-17-2010, 05:19 PM   #7
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QuoteOriginally posted by JeffJS Quote
You Do know that the DIAL, has no affect on the aperture setting on a K (or M) lens, don't you? Or are you talking about the Aperture ring? Either way, These lenses only stop down when you press the green button or when you snap the shutter.
QuoteOriginally posted by stevebrot Quote
To summarize the above. The lens will remain wide open in all modes except M. Due to weirdness of the metering system, it may be necessary to chimp and adjust the exposure up/down. You can also use the optical preview for metering if that works better for you.

Wow... I must really be loosing my mind, because I could of sworn(up and down) that my K lenses all responded to the aperture ring manually without stopping down... in fact... I could or sworn that I was using it just recently on a scenery shot at f11 thinking... wow! an I ever glad I don't have to force focus because the screen is so dark. In fact... I know the viewfinder was dark due to the ring setting!

Therefore, am I to conclude that there was something wrong with my camera prior to today or am I going mad?

PS. I've been on allergy medication for a few days now. I guess its taking its tole on me
07-17-2010, 05:34 PM   #8
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QuoteOriginally posted by JohnBee Quote
Wow... I must really be loosing my mind, because I could of sworn(up and down) that my K lenses all responded to the aperture ring manually without stopping down... in fact... I could or sworn that I was using it just recently on a scenery shot at f11 thinking... wow! an I ever glad I don't have to force focus because the screen is so dark. In fact... I know the viewfinder was dark due to the ring setting!

Therefore, am I to conclude that there was something wrong with my camera prior to today or am I going mad?

PS. I've been on allergy medication for a few days now. I guess its taking its tole on me
You are going mad. Might be the allergy pills too (same difference)...lay off the Benadryl for a week and then see how it works.

All K-mount lenses focus/compose wide open on your dSLR unless the aperture lever has been physically removed or chopped off. Your non-A Pentax-K lenses should only stop down at exposure time, when green button metering, or when using the optical preview feature and then only when the camera is in M mode.

To make it easier:
  • Examine one of your Pentax-K lenses with back cap off when it is off the camera
  • It should be stopped down to the aperture set on the ring
  • Manually move the aperture actuator lever
  • The aperture will change to full open
  • When you mount the lens on the camera, the lever engages the coupler in the body and opens the lens
  • When an exposure is made with a non-A lens, the coupler releases the lever to stop the lens down to the aperture set on the ring just prior to exposure and engages it to open the lens back up after the exposure is made
  • When you engage the optical preview, the coupler does the same thing to stop down the lens
Note that this action is somewhat different when the aperture ring is in the "A" position on lenses that support that feature. On those lenses, the lever moves the appropriate amount for the aperture set by the camera body.

As for testing that the aperture is stopping down at exposure time...That is easy. Stop the lens down to f/8 in M mode with the shutter speed at 1s. Look into the front of the lens while doing the exposure. You should see the lens stop down and reopen. Put the camera in P mode and do the same thing. The lens should remain wide open for the duration of the exposure.

If the lens does not stop down for exposure in M mode, there may be a broken linkage in the lens. Check that the lever works the aperture properly when the lens off the camera. On some older film cameras, it was possible for the arm to slip past its coupler if misaligned. This is not possible on your K20D. The only way for the lever to fail to engage is if it has been shortened (snipped/sawn off) at some time. There is an outside possibility that the lever might be bent over enough to jam outside its gate on the body leaving it wide open at all times, but this would be very unusual.

If your lens is always stopped down when mounted to the camera and there is nothing wrong with the lens, there is something wrong with your camera.


Steve


Last edited by stevebrot; 07-17-2010 at 05:52 PM.
07-17-2010, 07:09 PM   #9
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QuoteOriginally posted by stevebrot Quote
You are going mad.
A crap! that means the wife was right all along!

QuoteQuote:
If your lens is always stopped down when mounted to the camera and there is nothing wrong with the lens, there is something wrong with your camera.
To avoid the loony bin, I'm going to go with "I think there was something wrong with it, and that its back to normal now"

Thanks for taking the time to explain this out.
It was very helpful.
07-18-2010, 09:02 AM   #10
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Actually, could be a lens problem, it seems to me - if the aperture lever on the lens is bent, broken, or otherwise defective. Or if something is preventing the lens from mounting completely - some people actually do this on purpose because they *want* the lens to stop down immediately when you turn the aperture ring. That way you can use Av mode normally rather than needing to use M mode as you normally do when using the aperture ring.

Anyhow, indeed, K-mount lenses *are* supposed to stay wide open except when they stop down to meter (green button or DOF preview) or shoot.
07-18-2010, 10:59 AM   #11
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QuoteOriginally posted by Marc Sabatella Quote
some people actually do this on purpose because they *want* the lens to stop down immediately when you turn the aperture ring. That way you can use Av mode normally rather than needing to use M mode as you normally do when using the aperture ring.
I actually thought of that too. But.. because I'm trying to build a collection, I simply don't have the heart to fiddle with such gems. Especially the amazing ones like the 35mm & 85mm's.
For what its worth, I have most of the primes starting at 28mm(except for the 30mm), though the prices are really what's keeping me from finishing(nasty).
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