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Old 30-01-2009, 10:12 PM
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Octane (Humayun)
IIS Member #671

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Join Date: Dec 2005
Location: Canberra
Posts: 11,158
Again, my opinion, but, I believe any astrophotographer worth his salt would not employ the method of taking darks and flats (this, especially, is absolutely ridiculous) to build a library and then use them, /especially/ when it comes to DSLR imaging. Dedicated astrophotographic CCDs are a different story, thanks to their exacting build qualities.

A true dark matched to your light is the best way to go. Of course, it would be even better if a dark could be taken at the exact same time the light was exposing, but, I don't think we're there, yet (will we ever?).

Just the tip of the iceberg: how would you account for the accumulation and buildup of hot/dead/stuck pixels on your sensor over time, and under very specific conditions, such as temperature and humidity? Certain pixels may show up at ISO-400, but, not at ISO-100.

To me, this means you'd need to build a library of darks (I won't bother to mention flats because the idea of building a library of flat frames is preposterous) which would encompass anything from the absolute minimum time you'd expose your lights (typically 3-20 minutes), at every ISO, say, for at least one hour per ISO and shutter speed. The time taken to build this fallible system is a waste.

You're better served taking your dark frames after your light frames, and your flats (with associated darks) either before imaging, or directly afterwards.

At the end of the day, I guess it depends on how exacting you want to be and what you consider a good astrophotograph. Unfortunately, I think there is but a handful of people who take this methodical approach, yet, their results speak for themselves.

All my opinions. Any insults, implied anger, bad grammar and bad spelling, are entirely unintentionalal. Sorry.

Regards,
Humayun

Quote:
Originally Posted by TrevorW View Post
Everyone entitled to their opinion I've used this process on occassions and wouldn't say that my images have been crappy or a total disaster, albiet I'm still in the learning stage.



and to quote another imager from his NGC2070 post if he doesn't mind

"Thanks Rob

The cloudy area is natural from what I can tell, and it was certainly in the data as it appeared. I took several frames at 3x3 binning first and these didn't have it.

I've used darks from a library I've built over several days - at timings from 0.5sec to 3,600sec and at various temperatures. I matched the library darks with the lights individually. I hadn't taken any flats for this one - yet.

The dessicant has been recently baked, so that sould be OK. __________________
Cheers
Chris
"
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