Dark Frames

[valleyman]

Is it possible to take dark frames any time of the day. and make a set of masters for each time set.

Like 1min darks 2 min darks 3 min darks etc, and have the CCD set at a regular temperature say -5c 

or do you have to take them at the same time as the Lights.

[Leveye]

It's best to take them directly after your lights. The sensor and ambient outside temps will be the same.

[johnrt]

If you have set point cooling on your CCD then go ahead and take some at the temp you will run the camera at when you shoot the lights. If not then as Leveye says best to do them after your lights to match the temp of the darks to lights.

[Russe]

I have a darks library for my usual exposure length of 300s. I stuck my camera into the freezers, wrapped in tin foil and a towel. Then I took 100 darks and afterwards put them into folders according to their temp. 1-5C, 6-10C etc.

[Russe]

The same I did for Bias. Those I put through DSS and only kept a master file of 100 Bias, threw the rest away.

The only ones you gotta take are Flats. What I do is - I usually don't touch focus or camera and take the flats the next morning.

[valleyman]

Ok have made Master darks at 1 min, 2min,3min at -5c with the CCD

Will make some 4min and 5min as well

Then do the Bias again at -5c all stacked with Nebulosity

[tingting44]

have a read through this, some really good info in there

http://stargazerslounge.com/topic/212778-sub-length-vs-sub-count/

defo worth a read 

[Physicist13]

there's always a lot of discussion about dark,flats,bias!!!

Darks: the main variation for darks (by far) is their temperature dependance. So its good to have a set of darks at a temperature close to those you take images at..within about 3deg c ish. Most good s/w will scale the darks for both exposure time (a simple scaling so you dont need different dark exp times) and for temperature. But the further away from the actual temp of the lights the poorer the scaling will be. you need a master from at least as many frames as the lights are likely to be.

bias: are temp independant. just take lots (100 or more!) exp at fastest shutter speed. make master and use that.

flats: are the ones you have to take using exactly the same optical setup as the lights (incl cam orientation)...although "artificial" flats in s/w can be equally good in very many cases (but cant deal with things like speck,motes or images with very small background regions).

Patrick

[Zakalwe]

The great thing about setpoint cooling on CCDs is that you can do the darks pretty much anytime. As long as you image at the same temperature then you can re-use the same set of darks (and bias) over and over.

Or you could junk the darks and use a bad pixel map and bias.