Originally posted by Cyril_K5 I had a similar problem. At first I realised that I didn't put back the rubber protection from the grip contacts and thought I touched these with my fingers but then I realised when it happened a second time that it was due to the batteries I was using. They were "non Pentax" unknown third party batteries that I have discarded since then. I now only use Pentax and Polaroid batteries and never had any problem since. I did try a timelapse with 400 exposure, the batteries almost went to depletion but worked perfectly fine
I had issues using the battery grip with AA batteries also. I have given up on these as well
It's not caused by third-party batteries. I've used nothing but genuine Pentax batteries and I suffer through the mirror-gone-crazy problem regularly. I shoot time-lapse professionally, so I run into it a lot, but it's not the time-lapse itself that causes it. It just appears to be a crap-shoot when it happens, no way to predict it, and the only way, so far, to replicate it consistently, is to run your camera in time-lapse mode for a while, not just 400 exposures. Since people have the problem when not shooting time-lapse, my theory is that the only reason it shows up more for me is purely the law of averages because of how much use my K3 is getting.
It's not the grip either. I don't even own the battery grip.
It doesn't appear to be temperature or battery voltage spikes/surges. At least if it's either of those, it's not being reported accurately in the EXIF data. I saw no real anomalies in EXIF data of the photos leading up to mirror-flap. The last photo before the issue shows no unusual temperatures or unexpected battery voltage changes. Could be it's not being recorded accurately, depending on where the temperature sensor is, or if the voltage spike/surge is happening in the split of a second after the last photo is taken... but as of now, evidence doesn't seem to support it being temperature or voltage.
If you don't shoot time-lapse or weddings/events professionally, journalism or even birds/animals/nature, it's probably not an issue to worry too much about... at least in the sense that it will cause you wide-spread problems. I shoot architecture professionally, and if I weren't doing time-lapse, I'd probably keep the K3 and not worry too much about it. However, if you have to depend on it to get specific shots that you cannot "do over", and if the camera is getting heavy use, then I'd rethink relying on the K3 until this issue is fixed.