Lights, Darks, Bias, Flats Query

[PembrokeSteve]

Hi,

Having problems trying to find any written guidance on this and I know the StargazersLounge is the place to find an answer.
My query is:-
If you shoot say 40 "Lights", then how many "Darks" would you also need to take?
Also if you were planning on incorporating "Bias" and "Flats" then, how many Bias and Flat frames would be required (for 40 lights).
Is there any quick reference guide/card one can refer to for this, or is it a trial and error thing at calibration/stacking stage.

Regards,

Steve

[steppenwolf]

3 minutes ago, PembrokeSteve said:

If you shoot say 40 "Lights", then how many "Darks" would you also need to take?
Also if you were planning on incorporating "Bias" and "Flats" then, how many Bias and Flat frames would be required (for 40 lights).

Aim for 20 of each type of calibration file. As Bias frames are quick and easy to capture you could take more but I have never seen any improvement unless you have bad columns on your sensor and are using PixInsight for your calibration routine and even then I remain to be convinced!

[vlaiv]

It really depends on camera that you are using. It also depends on software that does calibration. If software that you are using uses 32bit precision for calibration - then you don't have anything to worry about, but if you use one that only does 16 bit for calibration then there is theoretical limit to number of darks, bias, flats and dark flats that you should use.

General rule with which you cannot go wrong is: as many as you can

 

[carastro]

There is no fixed amount, darks get as many as you can but I would say 12 - 15 is sufficient, if you have a set point cooled camera you can make a library of darks and re-use them and ditto with the Bias.

I normally do about 15 flats regardless of how many light frames I took, but if you are using filters you'll need separate flats for each filter.  

HTH

Carole 

[ollypenrice]

It would help to put your kit in your signature since advice will vary with equipment. I agree with Steve that 20 of each (though probably more for bias) will nail it.

However, if you are using a DSLR it is by no means certain that darks will help you. Many DSLR imagers prefer to dither-guide and to use a master bias instead of a dark. If you are not guiding then the dither will probably happen automatically through random tracking error. The problem is that the dark current is very sensitive to temperature so the darks may not be taken at the same precise temperature as the lights, so doing as much harm as good in many cases.

It is a good idea to use a master bias as a dark-for-flats. Depending on your software, this may or may not be done automatically at the stacking stage.

Olly

[spillage]

When running my dslr I always dithered and then ditched the darks, just used flats and bias. Not sure if this applies to the cmos sensor or just dslr but the asi1600 seems okay without darks when dithering.

[PembrokeSteve]

Many thanks for your advice. Much appreciated.
Wish this weather in West Wales would improve.
Clear sky's it seems ..so I think, lets get my new NEQ6 set up and do some test shots with my Canon 450D.. I go outside and it has clouded over!!