Max Duration of Very Long Exposures

<p>How long can a DSLR shutter be left open for very long exposures such as 30, 45, 60... minutes? I remember hearing somewhere that sensors can heat up after a certain amount of time. With film I've gone well over an hour but there's no sensor heating up, cooling off, etc... On my D7000 I've gone about 15-20 minutes max with no problems. Is this even an issue? Was it <em>ever</em> an issue? I know you can stack photos/HDR for similar effects but there are times when I would like to shoot one <em>very long</em> exposure. Thanks.</p>

I would think they'd have some kind of protection built in if damaging the sensor was a possibility. My guess is that

 

battery life is the real limiting factor here.

<p>I made several circa 90 - 120 minute exposures on my D700 with an extra battery via the the vertical battery grip. This never effected the sensor - maybe I got lucky but I never had an issue with an uber long exposure so long as I had enough battery power for the shutter to remain up and for the noise reduction afterward.</p>

<p>I suspect charging/resetting and reading data off the sensor is what heats it up, so video would be more of an issue than a still. I'd expect noise to build up over the exposure, and I've generally found the risk of blowing a highlight or something interfering with the exposure (for astronomy, a car appearing over the horizon, someone waving a torch around, someone kicking the tripod...) means it's almost always worth taking multiple shorter exposures and blending them, although I guess you could fall below the minimum sensor read level. I wouldn't expect it to hurt anything on the electronics, though. I always vaguely wished someone would do a genuine 24 hour star trail exposure from one of the poles (just because they could), but I've only seen stacked images. :-)</p>

<p>Depending on the camera model, your long exposure images may show the effects of amp noise in the form of a purple blob or haze, usually near the edges or corners.</p>

<p>There is no physical harm in shooting long exposures.</p>

<p>This is really a matter for specific sensors/models rather than a digital or even marque characteristic. Much also depends on the settings (with or without in-camera noise reduction, etc.). The ISO chosen is another important parameter. Tolerance of "noise" is another biggie. As an old GAF 500 shooter, I can stand a lot of noise (the digital <em>analogue</em> of grain)<br>

As for polar star trails:</p>

<ol>

<li>It's COLD out there!</li>

<li>If you'll fund me, I'll volunteer!</li>

</ol>

<p>No? Well, hope springs eternal. <br>

God Jul to all of you.</p>

 

Remember that film suffers from low-intensity

reciprocity failure, and that an hour's exposure on

film is probably only the equivalent of 5 or 10

minutes with a digital sensor.

 

Even with a DSLR set to 50 ISO, an hour-long exposure would require either a very small aperture or an extremely low level of light not to be overexposed.

 

Besides, digital capture enables you to "stitch" multiple short exposures together to simulate LE effects like star trails, etc.

 

I have seen the "purple blob" effect on a very early digital bridge camera, where the small sensor size and power hungry electronics conspired against long exposures. Never seen it on any recent model of DSLR though.