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04-10-2008, 08:19 PM   #1
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Long exposures and in-camera noise reduction

I've taken some long night-time exposures - 10-20 seconds - and it seems that the in-camera noise reduction (*ist DS) takes about the same amount of time as the original exposure. My un-scientific observation.

In my old film days, I took some lo-o-o-ong nighttime exposures (startrails -45 minutes +) - if I do the same using my DS, am I going to to have to wait for 45 minutes for the noise reduction process to complete? If that's the case, what happens to the image if I turn noise reduction off? Or, is it harmful to the sensor to take that long an exposure?

04-10-2008, 08:47 PM   #2
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QuoteOriginally posted by ChipB Quote
I've taken some long night-time exposures - 10-20 seconds - and it seems that the in-camera noise reduction (*ist DS) takes about the same amount of time as the original exposure. My un-scientific observation.

In my old film days, I took some lo-o-o-ong nighttime exposures (startrails -45 minutes +) - if I do the same using my DS, am I going to to have to wait for 45 minutes for the noise reduction process to complete? If that's the case, what happens to the image if I turn noise reduction off? Or, is it harmful to the sensor to take that long an exposure?
Unlike your old film days you never took a "dark frame" to subtract from the original exposure.
This is what your digital camera is doing. And the exposure is equal to the original exposure..
You can shut NR off and not have the looong wait (exactly equal to the first exposure) as the dark frame is taken but you will increase the noise and possibly have "amp glow", which is a reddish "hot spot" produced by the sensor.
Some people prefer to do their own "dark frame" and then combine it w/ their real exposure. If all your timed exposures are the same length, then you only need one dark frame for a set of images. Best to ask the "astro people" the nuts and bolts of this proceedure....
JPEG Dark Frame Subtraction
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04-11-2008, 08:52 AM   #3
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Thanks Jeff. That's kinda what I figured - take a 45 min exposure , wait 45 minutes for the dark frame process. Bummer. I remember one time taking a 3 hour exposure - set the alarm to get me up. Wow - 6 hours for the DS!!

If I were to undertake sure an event, does anyone know if sensor damage could occur? I'm concerned about the heating of the sensor during a very long exposure.

The driving force behind all this is that for the first time since I've owned the DS (2 years now) I'm going to be in a very dark nighttime environment and wanted to try to replicate what I did in my film days.
04-12-2008, 04:28 AM   #4
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I've seen some veeeeeeeery long exposure images here and they all didn't turn out nice, not worth the wait.

So, before investing your precious time I suggest to try it out with an hours long exposure taken overday in a dark room (windowless room, I mean).

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