Dark Libraries?

[pook]

Can I build up a library of dark files for different exposure times and temperatures, so as to not waste any clear sky time? For instance, can I have a set at 5C, 50 exposures of 1 minute, and call that set 5C-1MIN, and then lets assume I take 30 subs at a similar ambient temp, can I just use the first 30 of set 5C-1MIN?

I hope that makes sense.

If so, while it may take ages to build this library at different temps and times, it may save work in the long run.

[RobH]

Yes, you can, and it's well worth doing.

The number of darks doesn't need to match the number of lights though.

You need enbough darks so that when you stack them to create a master dark, you remove any random noise from them during the stacking process, and therefore don't end up adding noise to your lights when you calibrate them.

You can also make a master bias......I now make my master bias from about 100 subs, and my master darks, around 30-50.

I've done a big section on calibration on my website.....you might find it useful.

http://stargazerslounge.com/imaging-tips-tricks-techniques/121457-articles-tutorials-signal-noise-image-calibration-levels-curves.html#post1602671

Cheers

Rob

[MG1]

I'd try and keep the libraries as fresh as possible though....over time your chip will change and you want to ensure that you are subtracting the correct darks info.

[Bizibilder]

It gives you something to do on cloudy nights! I take all my dark "libraries" in the garage - I find it is pretty close to ambient - so I run off 40-50 darks for each exposure time and ISO that is likely to be used, make a note of the temperature and file them in folders under temperature each folder having darks for each exposure time. I invariably work at ISO 800 so all my darks are at that setting. I now have darks for 30sec, 1 min and 2 min for every two degrees from -4 to +10. I'm just waiting for the weather to warm upto do some more!!

[RobH]

It's true that the chip changes over time, but I find that a good set of darks/bias will last for 6 months in practice.

[MG1]

That's good to know...cheers Rob. If I can reuse where possible I do.

[pook]

Thanks guys! That's brilliant. The thought of creating all these files each time I tried to shoot anything was slightly depressing.

So long as I keep them up to date twice a year I shall start work on this right away.