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01-20-2014, 05:33 PM   #1
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Pentax K-7 Meter Glitch?

My K-7 has around 95,000 actuations on it (after 30 months), just to put into perspective that it's used very heavily. This weekend I was digitizing some plate glass negatives from the 1920s and the meter began reacting strangely.

I've had some issues with the meter giving me different readings in LV versus non-LV modes for a while. And, interestingly, at different shutter speeds the images turn out the same way depending on if the camera is in LV or non-LV mode. For instance, looking through the viewfinder the meter may say f5.6 and 1/125th. In live view, it might say f11 or f16 at 1/125th. Notably, the LV meter readings have been in-line with my Eric-CLA'd film SLRs, all of which meter out within a third stop of each other pretty consistently. Taking the image at the suggested setting in either mode results in the same, correct exposure despite the aperture being two or more stops different. This has also been increasing with time in the last year, when I first noticed the meter readings were off by about a half stop.

This weekend,however, it began reacting very strangely. After about 30 minutes of reprographics, I'll let the camera site and cool down for 30 while I copy the images to the PC and do some file organization. That's also to spare me standing on a hard floor for hours at a time. Late in my second set of images, after about 50 (total) minutes of imaging in a two-hour period, the meter began reacting wildly and unpredictably. In LV mode, it would suddenly make ten-stop metering swings. I do reprographics in manual mode, so the settings remained the same but light meter said that the light was shifting from more than five stops under to more than five stops over and then back every few seconds. Oddly, if I took an image at f8 1/125th when the meter said it was underexposed, the image was black. The same settings when the meter read proper exposure and the image was fine. The same settings when the meter said the image was over exposed, and the image came out almost pure white. I'm indoors under fixed lighting, so there aren't be any variables due to actual lighting.

So, does this sound like a software or hardware issue? My concern, obviously, is that something is seriously wrong with either the meter components or the motherboard. I'm using the last firmware edition, but is it possible for firmware to be corrupted?

01-20-2014, 06:56 PM   #2
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What sort of interior lighting? If it's fluoro (either compact bulbs or standard long flours) the metering will vary as the lights flicker on and off. May not affect live view as the camera is operating like a "video camera" in this mode.
01-20-2014, 08:00 PM   #3
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You don't have bracketing on, do you?
01-20-2014, 09:29 PM   #4
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Last time my k7 metering went a bit unpredictable, the three position metering mode switch had been accidentially bumped into an "intermediate position" between matrix and centre weighted.

01-20-2014, 11:34 PM   #5
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So it is fluorescent lighting, two naked bulbs behind white acrylic with a negative on top and a macro lens. Bracketing was off. The meter was set for spot so I could take a fine-point reading on an area that's about 15% gray (the baseline I use for contrast control) and then the settings were all done manually.
01-21-2014, 10:22 PM   #6
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Fluoros 99% likely culprit then. They turn on and off too quickly for the eye to see, but the camera is faster and could expose as if one or both lights are off. Try using a different light source.
01-22-2014, 02:39 PM   #7
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I'll try other lights, but it's weird the issue would start after I've done this set up for a year. One of the techs I received a quote from suggested resetting the camera and reinstalling the firmware updates. So I may give that a go tonight.
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