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12-14-2013, 12:31 AM   #46
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Im betting the aperture drive motor is faulty. try it in full manual set shutter and aperture and iso then do multiple exposures and see if the problem repeats

12-14-2013, 12:54 AM   #47
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QuoteOriginally posted by OldNoob Quote
Im betting the aperture drive motor is faulty. try it in full manual set shutter and aperture and iso then do multiple exposures and see if the problem repeats
I've got a few hours tomorrow, believe me, I'm going to do quite a few tests..

Edit: I'm also going to try it with my Tak 55, no aperture levers involved...

Last edited by altopiet; 12-14-2013 at 01:02 AM.
12-14-2013, 11:54 AM   #48
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QuoteOriginally posted by altopiet Quote
I've still got it on the card, but unfortunately the shots displays on the camera with the same problems...
In that case I agree that's definitely a problem then, the exposure shouldn't be different between the two... I would contact Pentax service and see what they have to say other wise it can more than likely only get worse.

Good point Oldnoob...

Edit: after thinking about it more it it couldn't be the aperture drive motor, since in the four shots each of the two examples of raw and Jpeg output show the exact same subject positioning along with the same exact date & time stamp. I presume these were taken in Raw+?

Last edited by Oldbayrunner; 12-15-2013 at 07:15 AM.
12-15-2013, 10:23 PM   #49
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QuoteOriginally posted by Oldbayrunner Quote
I presume these were taken in Raw+?
Yip, RAW+. I've taken the whole Sunday, using various lenses, my Tak 55/1.8, FA28-80 and the DA70 again, using various settings from manual to P and everything else, continuous AF shooting to interval shooting and anything else I could think of, a few hundred shots....I just couldn't get any repeat of the problem with the shots already posted....I hope it was a once off fluke..

12-17-2013, 10:31 PM   #50
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Perhaps there was a bad connection from camera to lens. In both cases the camera was commanding the lens to F1.4, but in the dark exposure the lens was receiving a different value and stopping down further. Perhaps there was some crud between camera and lens, or there's an intermittent failure inside the camera (since it happens on more than one lens). I don't know any specifics of how the camera signals to the lens and how feasible this could be.
12-18-2013, 11:11 AM   #51
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QuoteOriginally posted by OutOfFocus Quote
.........
I don't know any specifics of how the camera signals to the lens and how feasible this could be.
........
The lens signals to the camera what its full open aperture is and by how many stops it can close down. Based on that and what aperture the camera wants the lens to be the camera will calculate how far to move the aperture lever. It is the extent that the camera moves the aperture lever that ultimately determines how wide the iris will open.

There are many different things that can go wrong. At one end dirty contacts could cause errors when the lens is communicating its maximum/minimum aperture capability to the camera and at the other it could be a mechanical/electrical fault with the aperture drive mechanism.

The motor itself is unlikely to be the problem as that same motor also lifts the mirror and preloads the shutter, so any fault in it would affect those also. The way it works is that the motor always turns the same number of revolutions and a solenoid actuated clutch engages/disengages the aperture lever so that it only moves the required amount. There are of course all sorts of things that can go wrong with that such as a weak solenoid, friction in bearings and so on.

Normally such problems as you are experiencing would be caused by a ticky aperture lever in the lens but if I understood right you are seeing this problem with any lens you attach.
12-18-2013, 06:24 PM   #52
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I have somehow the same issue with the other K-30, at first I thought it just about a "user" issue, but then again I set mine on Full M. Center weighted and intentionally use a burst mode, on all of my lenses the camera produced, under, over, under, over exposures, I immediately contacted local service support and hopefully send the camera in Pentax Cebu and have it check in no time.
12-18-2013, 06:25 PM   #53
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Moreover, I observe this happens whenever I change my aperture settings...

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