Author Topic: Collection of Darks and Bias useful?  (Read 318 times)

Offline GeBs

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Collection of Darks and Bias useful?
« on: 2019 October 03 07:41:53 »
Hello,
I am relatively new in astrophotography and recently bought the book "Inside PixInsight" from Warren A. Keller. He writes at the beginning of the book that it makes sense to create a collection of darks and bias, as those can be used over several weeks, possibly even months.
I have now recorded several hundred darks and bias with my Canon EOS600Da DSLR instead of lights in cloudy nights.
I sorted the bias according to ISO and sensor temperature in 5°C steps. The darks are also sorted by exposure time. The file names I have all changed with Advanced File Renamer, which I have ISO, exposure time and sensor temperature in the file name.
Then I created masters from the bias and darks.

So e.g:
- Bias ISO800 21-25°C (156 images)
- Bias ISO800 26-30°C (78 images)
- Bias ISO800 31-35°C (185 images)
Same with Darks:
- Darks ISO800 120s 21-25°C (156 images)
- Darks ISO800 120s 26-30°C (176 images)
- Darks ISO800 240s 26-30°C (78 images)
- Darks ISO800 240s 31-35°C (185 images)
- Darks ISO800 600s 26-30°C (99 images)
- Darks ISO800 600s 31-35°C (74 images)

Now I only need to create lights and flats at night, determine the average sensor temperature of the lights and flats and calibrate everything with the finished bias and darks.
Is this all so correct and usable and what Warren A. Keller means in his book or is this all nonsense and I really have to "waste" half the night for darks?
I would appreciate your feedback and hear how you handle darks and bias.

Greetings from Austria
Gebhard

Offline rakla

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Re: Collection of Darks and Bias useful?
« Reply #1 on: 2019 October 06 02:56:08 »
Hi Gebhard

I use a modded Nikon 7200 DSLR with a similar approach but stick to seasons for now, which of course means a larger temperature range. I then take lights and flats and choose the bias and darks from my library, based on the season / approx. temperature.

This seems to work fine with my setup.

/Ralf

Offline GeBs

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Re: Collection of Darks and Bias useful?
« Reply #2 on: 2019 October 06 23:32:03 »
Thanks Ralf for your answer. Do you think that the season is important from the weather condition more than only the sensor temperature?

Do you know if this library approach will also work with cooled CCD cameras? Personally I think this must work better because you have a constant sensor temperatures.

Anyone else here in the forum who will share their how to make and handle darks and bias?

Greetings
Gebhard

Offline John_Gill

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Re: Collection of Darks and Bias useful?
« Reply #3 on: 2019 October 07 02:16:38 »
Hi,

Some calibration files are temperature dependant.  Bias and flats files are quick to take, so I run those after an imaging session.  Darks are the issue, especially with a DSLR.  Some people put their DSLR in the freezer until the required temperature is met and then they do darks.  I do not have huge temp differences so I just bring the scope inside and run my darks at whatever temp.  Now I am using a cooled camera (ZWO 1600mm), I bring the scope indoors, set the temp on the camera and run my darks.

I think the temperature and gain combinations can make the library large and then you need to redo the library every 6 months which becomes a pain.
So, a library will work for either DSLR or a cooled camera ... I just prefer to get calibration frames per imaging session.

space is not black
John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline rakla

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Re: Collection of Darks and Bias useful?
« Reply #4 on: 2019 October 20 06:25:51 »
Gebhard, i was referring to the seasons mainly to indicate an approx. temperature range. Afaik there are no other aspects with regards to darks and bias frames. When it come to actual pictures humidity is an issue for me in spring / autumn.

As John points out it takes flats and bias frames need little time. I take flats with each imaging session and bias once in a while. I tend to take the flats at dusk using the natural skylight. This works well for me, as I usually setup before nightfall anyway.

/Ralf