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oldannie

Collecting darks

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I want to collect some 600sec and 300sec darks, maybe 20/30 of each over as short a period as possible, using Atik 460ex, mono. I have my cooling set to -15 deg C (max for the 460 is -25) and the weather forecast is telling me it's going to be about 8 deg C overnight though as we're quite high and rural it may well be lower.  Using the sequencer on Artemis capture can I safely let everything run for 6/7hours (in my pulsar) or would I be better acquiring darks over shorter periods?  Have only just moved from DSLR to CCD and not overly technically minded so full of naive questions!

 

Annie

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Since your camera has set point cooling, you can take your darks whenever you want, as long as its dark enough so you don't have any light leakage

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Are you sure you want to go to all this bother? We have a 460 EX mono in one of our rigs and, after an initial test with darks, we decided they didn't work. They don't work on our Atik 11000 cameras either - or not as well as alternative methods.

We use a master bias as a dark and found that it gave a result indistinguishable from a master dark of precisely the right temperature. Given that the cooling is on the feeble side with this camera, so it may struggle to maintain the set point in summer, a master bias may do better than a master dark at slightly the wrong temperature. We go after the faint stuff here so we stretch very hard indeed, meaning that calibration matters. We just don't think much of darks...  

Olly

 

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I did wonder about the efficacy of darks Olly and no I would rather not go to all that trouble.  - does that mean you just use flats and bias.   I would expect to take around 20 flats and loads of bias?

 

Annie

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I must confess I sometimes don't bother with darks (with the same camera as you Annie).

I have tried Olly's method of using a master bias for a dark and quite honestly it made a proper mess of the result.  Left it out and image was just fine.  

I'd do a few darks and keep them in a library, but don't make too much work out of it as the chip on this camera is pretty good.  

Carole 

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That would seem to be a sensible compromise Carole - Cheers!

Annie

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