Question about Darks

[kz1bob]

Hi All,

This is probably a nube question, but the best way to stop being a nube is ask for help, right :-)

When you take your 'darks' do have a set of darks that you use when you process your images or do you take new darks with each session so that they were taken in the same environment as your images?

To a certain extent would ask the same about taking flats, as well.

All advice very appreciated.

[RichLD]

Hi there

Do you have a camera with set point cooling? If you do it's possible to build a darks library outside of precious imaging time that are the same duration and temperature as your light exposures.

Flats, however,  are intended to correct visual imperfections in the optical train such as dust bunnies and vignetting so need to be taken at the end of each imaging run, unless of course you have a permanent set up where the camera orientation and focusser position never shifts and no new dust appears etc. I know some imagers who regularly reuse their flats but in general you need to generate them at the end of each session, especially if you repeatedly tear down and reassemble your kit like I do ?

Hope that make sense ?

Rich

[SteveNickolls]

This is a 'depends' question. If you are thinking of using a DSLR, because it's not possible to control the temperature like with a dedicated Astro-camera, I'd probably not bother taking dark frames. Unless you take a lot of them you can introduce more noise into the final image. My journey into DSLR imaging has been with Alt-Az mounts where you take many short exposure light, dark, bias and flat frames. Initially I was taking around 50 dark frames and more recently I have been using stock frames at the same ISO and exposure values. In the future I'm not going to bother with dark frames, partly down to the temperature issue and also as I understand it Canon cameras do a lot of 'magic' to dark frames meaning their value is at best lost. Flat frames however are very useful and need to be taken at each imaging event without altering the optical path of the camera/telescope. If you are going to use a dedicated asatro-camera then I'm sure others will better advise you. 

Cheers,
Steve

[kz1bob]

I will be starting with a DSLR. It is an Olympus E-500. Most of the world is using Canon, but I will give it a go with my existing camera to start and then feed the monkey as I learn.

In my case, I will be tearing down after each session. I am thinking there will be a lot of trial and error, but hopefully, the error part will be minimal and the trial part proves to be half the fun.

[ollypenrice]

Yes, if you don't have set point cooling I wouldn't bother with darks. You are likely to do more harm than good. It would almost certainly be better to use a master bias (re-usable) in place of a dark and, if you can, dither your subs (move them a little between each capture. Many capture programmes can automate this.)

With our permanent setups our flats last months but if you are mobile you have to re-do them. If using DSLRs try to de-activate the chip-shaking cleaner for AP or it will defeat the flats by shaking the dust around.

Olly

[kz1bob]

Thanks Olly for the chip shaking tip.