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08-08-2014, 05:53 PM   #1
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KX Taking Dark pictures

Hello.... Ive searched and searched online and cant find any clues as to whats going on with my KX. Problem I'm having is after first starting up my camera the first 7-8 shots come out almost pitch black, Ive even pointed it at the sun and it looks like a dim 5w bulb. After about 7-8 shots not changing any setting whatsoever it starts taking picture perfectly until I power off and it has to start up again. Any clues? Could the light meter be bad, or perhaps the Sensor is dying? Ive done software update to the latest, full reset , different lenses Pentax 18-55mm kit lense and my Pentax 50-200mm lense with no change. Ive had it for about 2.5yrs now and have about 7k actuations.

08-08-2014, 06:19 PM   #2
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Thats pretty strange. I'm no expert but if I had guess I would have thought it could be something sticky around the aperture actuation.

You could confirm if metering is Ok by sticking the camera in manual and looking at the meter (don't need to take a photo) while adjusting shutter / aperture. Is consistent over a period after startup? Does the suggested exposure follow the "Sunny 16" rule (on a sunny scene, f16 + approx 1/125).
08-08-2014, 06:46 PM   #3
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The checks to do are switch it on and point it at your face and press the shutter with no flash.


Observe the aperture iris, is it closing all the way down.


Check the aperture the camera thinks it was using.


What your looking for is the iris stopping down to f16 by observation, but the camera thought it was wide open so records in the exif f4 or f5.6 or thereabouts.


If this is happening theres an aperture issue.


Your fault could be explained by the aperture closing all the way down when the meter tries to use a wide open setting and this state remains until it warms up or loosens up in use after 6 or 7 shots and then the camera controls the aperture correctly.


In other words is the aperture obeying the camera


If the exif records the used aperture correctly the fault lies elsewhere and further testing is needed.
08-08-2014, 07:37 PM   #4
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Are the images evenly dark, or is there unevenness from top to bottom? The camera shutter is 2 "subassemblies" that move in sync and maybe they aren't working correctly immediately after power up.

Another troubleshooting tip to rule out sticky aperture on the motor. Turn on the camera, Av mode, stop all the way down (approx f22 with your lenses). Those settings tell the camera to exposing for minimum aperture. Are the first few images still too dark?

08-08-2014, 07:47 PM   #5
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  • Take the lens off the camera in M mode with focus set to manual
  • Set shutter speed to 2s
  • Find the aperture actuator coupling (9:00 o'clock on the inside of the mount as you face the front of the camera)
  • Confirm that the coupler is at the bottom of its travel (full-down position)
  • Release shutter and confirm that the coupler travels to the full-up position at the beginning of the exposure and returns to full-down when the exposure is finished
Anything other than this behavior indicates a fault in the actuator motor or its controller or a broken mechanism. This is the most likely cause. A malfunctioning shutter will normally result in the top being exposed differently than the bottom or a black bar top or bottom.


Steve
08-08-2014, 08:12 PM   #6
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QuoteOriginally posted by kiwi_jono Quote
Thats pretty strange. I'm no expert but if I had guess I would have thought it could be something sticky around the aperture actuation.

You could confirm if metering is Ok by sticking the camera in manual and looking at the meter (don't need to take a photo) while adjusting shutter / aperture. Is consistent over a period after startup? Does the suggested exposure follow the "Sunny 16" rule (on a sunny scene, f16 + approx 1/125).
Ok so Ive attached a couple pics of what I was talking about, Ive tried the suggestion, and whats weird is I put it in M mode and moving the Fstop up made the images brighter. When I got all the way to 40 instantly made the pictures almost normal. These picture were taken at ISO 320 1/100sec at F4.0 Focal length 50mm, and were taken within a second of each other with no changes at all in the settings
Attached Images
View Picture EXIF
PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
08-08-2014, 08:23 PM   #7
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I would check the battery in the camera first to see if it is still fully charged. If the battery voltage drops below certain threshold, sometimes, the metering may be off; just a thought...
08-09-2014, 11:55 AM   #8
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I disagree.


The exifs from both images show this :-


iso 320 for both images


f4 for both images


1/100 for both images




The metering is correct or the second image would not be correctly exposed. There isn't a connection issue with dirty contacts or it wouldn't correct itself after a few actuations and then behave incorrectly again then correct itself again without disturbing the lens mount.


This behaviour is exactly as I predicted. The camera thinks its controlling the lens but sometimes it is and sometimes it isn't.


The confirmation is in looking at the lens iris as it takes the underexposed images, I suspect you will see the iris stops fully down and then suddenly stops partially down as the camera behaves itself. This is very likely due to a fault in the aperture control, exactly as I expressed in my earlier post.


Have a go at this simple test.

08-09-2014, 01:23 PM   #9
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QuoteOriginally posted by Imageman Quote
exactly as I expressed in my earlier post.
Get used to it. If I could count the number of times...

What'cha wanna bet that the actuator is munged in a manner similar to that of another K-x/r/m a few months ago where the user was having the same symptoms? I will look for the thread. There were photos.


Steve
08-09-2014, 01:30 PM   #10
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Im used to it steve.


Im a photographic god and nobody is worshipping me, (petulantly stamps little foot)
08-09-2014, 01:46 PM   #11
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QuoteOriginally posted by Imageman Quote
Im a photographic god and nobody is worshipping me, (petulantly stamps little foot)



Steve
09-23-2014, 11:48 AM   #12
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I had a similar problem when I was repairing my K-2000.

The issue was the mirror/shutter is out of sync with aperture actuator. Somehow the gear box got into wrong state which the mirror flip and aperture actuator is not firing at same time. The actuator actually moves to fully closed position even the aperture been set to wide open. This is the way the mechanism works to calibrate aperture position by fully close the aperture first then set to the dialed aperture instead of simply travel from the full open position to dialed aperture. ( you can see that from the lens as advised before)

The problem was, there is a solenoid that controls when actuator engage to the gears. It became sticky. The one I have actually is out of position which not allow it to retreat (a self-inflicted wound ). Push the solenoid actuator back (not aperture actuator that you can see from the mirror box, this one is inside of body) fixed my problem. Yours likely is freeze to the rest position instead which few shocks (take first few picture) loose it up.
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