Bulb setting - how long is safe

[hector49]

Hi there - haven't posted for a while as I have been out shooting and trying different things that I have read here and in some books.
But I have a question on using the bulb setting. I searched, but could not find anything in the forum, so my apologies if this has been covered already.
My question is, how long can I leave the shutter open using the bulb setting without causing any damage? Is it infinite, or is there a general rule of thumb for this?
I am planning on taking some lightning shots for the first time and as we have been having some storms lately, and there are a couple in the forecast for this week.
Any comments/suggestions/recommendations would be helpful.
Thanks in advance.
Hector

[inkista]

Some folks use shutter speeds that are hours long for star trail photography. You usually have to worry about your battery draining before you have to worry about sensor damage. However, the longer the exposure, the more heat will be building up in the sensor, so I wouldn't posit that "infinite" was safe.

[RexK_Cozumel]

For lightning shots you really dont need too long of a shutter speed. Certainly nothing anywhere close to damaging your sensor.

[Doug Pardee]

You're not going to damage the sensor from exposure to light. You might get an all-white picture if you seriously overexposed, though.

The only thing that you need to be careful of is pointing the camera directly into the sun for a length of time with mirror lock-up and the shutters closed. I don't know why anyone would do that, but apparently occasionally someone does. If you did that, the closed shutters would be exposed to direct focused sunlight from the lens. Normally the mirrors would keep the sun from reaching the shutters except for a short time just before and after the photo is taken, but if you're using mirror lock-up the shutters are unprotected.

Especially on older digital cameras, you might have a problem with a particular image taken with a really long exposure, due to heat build-up near the sensor. This "amp glow" typically shows as a reddish cast in one corner or along one edge of the picture. This doesn't damage the sensor, it just messes that photo up a bit. I haven't heard complaints of significant amp glow in cameras new enough to have, say, 8 or more megapixels.

[Gonzo13]

I just did some lightning shots not to last month. I think that the longest exposure that I had for it was maybe 40 seconds.

[hector49]

Great - thanks for all the info.
I had read that to get the perfect lightning shot, as it is so unpredictable, that you needed to leave the camera open for the shot - ie, use bulb, and press the release and wait.
Ideally in a heavy storm when lightning is fast and furious, this wouldn't be an issue, but for storms that aren't so heavy, but have great lightning at a good distance, it could be an undisclosed amount of time between strikes.
But, the comment around 40 seconds seems to make sense to me now.
Too bad we can't photograph thunder - you know when that's coming.
Anyway, thanks again.