[slip]

try to mimic the same shot as above, but keep it in manual instead of auto.is it possible to have it on auto EV compensation? maybe it compensated on the one photo and not the other?
try different metering patterns as well. (center, spot, etc)
if it does this in manual, I would think it needs a repair.

good luck

randy

[Deimos]

I had the exact same problem as you with my K-r

https://www.pentaxforums.com/forums/general-technical-troubleshooting/150836-...tos-black.html
(samples deleted)

Where I would take two shots in good light and one would be ok and the other way underexposed with identical or similar settings. It would do this sometimes but not others, frustrating.

I sent it into Pentax, they kept it for awhile. Eventually they said they couldnt diagnose the issue and sent me a replacement. Maybe send it in if you can?

[br.davidson]

Thanks for the help everyone. The photos I posted here don't show it as much, but I have another that clearly shows the aperture is way smaller on the dark photo. It seems that bobpur's diagnosis was correct.