Intervalometer, dark-frame, long exposure - Script Writing - CHDK Forum
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Intervalometer, dark-frame, long exposure

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Offline yorugua2

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Intervalometer, dark-frame, long exposure
« on: 02 / August / 2010, 19:05:58 »
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I'm looking for a scrit that will take a dark-frame, then a picture with 65 seconds of exposition, a drak-freme, then a picture with 65 secondos of exposition, over and over again for one hour.
The camera is a Canon A450, is for astrophotography.
I'm really lost.
Help!!!
Thenks
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Offline reyalp

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Re: Intervalometer, dark-frame, long exposure
« Reply #1 on: 03 / August / 2010, 13:42:28 »
There is currently no way to take dark frames alone with CHDK.

It is fairly easy (if you are a programmer) to modify CHDK to capture the raw before the dark frame is subtracted. I did it for a540 here http://chdk.setepontos.com/index.php/topic,1998.0.html

If you want a dark frame for every frame, then why not just let the canon firmware do it's dark frame subtraction ? Or perhaps I've misunderstood your plan.
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Offline stargeezer

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Re: Intervalometer, dark-frame, long exposure
« Reply #2 on: 03 / August / 2010, 18:25:03 »
Quote from: reyalp on 03 / August / 2010, 13:42:28
If you want a dark frame for every frame, then why not just let the canon firmware do it's dark frame subtraction ? Or perhaps I've misunderstood your plan.

There is much discussion in the astrophotography world of dealing with dark frames.  The most popular opinion is to build up a library of darks for both exposure time and temperature, and then let software remove the darks.  This allows the imaging time to be spent totally in imaging, and make the darks when the sky is not so friendly.  Many think that the internal dark frame subtraction actually removes good data.  I use the internal dark frame subtraction as my camera tends to change too much during the night, but I am in the minority.  I suspect the original poster was trying to build the dark library at the same time as imaging, I could see that being beneficial also.
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Offline reyalp

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Re: Intervalometer, dark-frame, long exposure
« Reply #3 on: 03 / August / 2010, 18:52:47 »
Quote from: stargeezer on 03 / August / 2010, 18:25:03
Many think that the internal dark frame subtraction actually removes good data.
This is something that could be determined objectively for CHDK cameras, using my before-and-after darkframe raw hack.

You can also generate a dark frame form the difference.
Quote
  I use the internal dark frame subtraction as my camera tends to change too much during the night, but I am in the minority.  I suspect the original poster was trying to build the dark library at the same time as imaging, I could see that being beneficial also.
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Offline yorugua2

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Re: Intervalometer, dark-frame, long exposure
« Reply #4 on: 03 / August / 2010, 20:03:29 »
First, thanks to both.
 I do not understand well that it is what does your patch
does it record a separated dark frame?
 I need the drak frame for the software that I use to process the photos.
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Offline reyalp

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Re: Intervalometer, dark-frame, long exposure
« Reply #5 on: 04 / August / 2010, 00:16:06 »
Quote from: yorugua2 on 03 / August / 2010, 20:03:29
First, thanks to both.
 I do not understand well that it is what does your patch
does it record a separated dark frame?
 I need the drak frame for the software that I use to process the photos.
No, it records the raw before and after canon dark frame subtraction.

Note that the patch in my post is only for a540, and against a very old version of the source, so it's not something you can use directly.

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