sensor effects from very long exposures?

I've heard it said that very long exposures (>30 min? hours?) may cause sensor damage, possibly due to heat buildup in the sensor. On the other hand, I have seen star-trail photos which clearly used extremely long exposures. Can anyone comment?

Quote:

---

Originally Posted by AlanK

Can anyone comment?

---

I'll comment ...

... It's my understanding that the "heat build up thing" is just someones "sound good theory". It's never been a problem with my long exposures.

What MAY be more of an issue is where the likes of Liveview is used, and the data is constantly being clocked out; can't speak for Nikon, but Canon have an over-heat protection mechanism built in for this circumstance.

I can vouch for Canon's over-heat protection... at least in the 7D. Though I've scoured my manual several times to find it without any luck (which doesn't necessarily mean it isn't there as I am sometimes horrible for plainly overlooking things), I have indeed seen a red thermometer icon appear on my Live-View screen once. Granted that was while the unit was sealed in an Ikelite dive housing, and I was using Live-View + a lot of macro focus seeking + IS. Once I saw the thermometer, I shutdown the camera and let it sit for a while, then when I retried it, it was fine and I have never seen that again since (though I never used Live-View while on a dive again).

- Bill

From Canon's Tech guru Chuck Westfall: "Long exposures pose no threat to the longevity of Canon's CMOS sensors in EOS Digital SLRs, but they will run the camera's battery down. If the battery voltage falls below a prescribed limit, the camera will shut off and any image data in the buffer memory will be lost."

Those star trails you mention are in 99% of the cases stacked photos.

They use alot of pictures taken over 1 or 2 minutes. If you have to leave the camera open for the equivalent amount of time (hours maybe) then something might happen: either your battery won't last so long, or something will be blown out (if you have anything but the sky).
Easiest way is to stack them :)