[random pentax user]

I wonder if very long exposure, about 2 hours, could leave any harm to my k-5, sensor damge etc.

[adr1an]

Lol - I was just asking the same question myself via the Search Feature....

What I found is: The answer is in the Astrophotography threads and in short - No.

I obviously am not answering from personal experience - but there appears to be numerous people w/ K10's (better it seems), K20's, 5's, 7's and x's that have all taken between 5 minutes up to one image I saw that was 2.5hrs...

The biggest issue is the Dark Frame Subtraction (or NR as its called in-camera) that kicks in and will double the time of the exposure as the camera takes its automatic follow-on built in DF after every frame - so 30sec will become 1min between cycles etc.... I believe you can turn it off in the K5 - but K20 and 7 users need to resort to the Debug Menu.

If you do turn it off - I'm guessing it would be worth while taking at least one DFS shot tho. It would seem that the Hot Pixel Noise is fairly Linear and Constant - so one shot should cover a range of long-exposure shots.

But ultimately - it would seem there is no risk of damage - just of decreasing Signal to Noise Ratio. Any Hot Pixels that start to present themselves due to heat should disappear as the sensor cools again. Some people in the Astro threads feel that multiple short exposures (of say 30 secs each) that are then stacked using a program like Startrails application is better in terms of getting good S:N ratio.