Image capturing darks flats etc advice please

[Spookyer (Brett)]

Image capturing

I have looked around the net and put this brief summary together, could more experienced people have a look please and check it and provide advice to improve it.

Dark frames, take with lens cap on, match temperature, ISO, exposure length - take at least 12 if possible. Compensating for noise from imaging sensor

Flat frames, take images of an evenly illuminated field (light box) with the same optical setup and orientation as the lights (focuser in same position etc). Temp not important. Aim for an exposure length that gives you a hump around the middle of the histogram. Are used to correct the vignetting and uneven field illumination created by dust or smudges in your optical train.

Bias frames, take with lens cap on, match ISO, exposure length at fastest shutter speed (1/8000 second), take a lot 30+, quick to do. Temp not important. Used to remove the CCD or CMOS chip readout signal from the light frames.

Light frames, actual shots of the subject, get as many as possible.


Cheers
Brett

[naskies (Dave)]

Hi Brett,

Looks pretty good. Don't forget "dark flat" frames - like dark frames, but matched to the same settings/duration as flat frames.

One thing - 12 dark frames might be a bit few, especially considering they're quite easy to take. If you have too few dark frames, you'll actually add noise to your final stack.

By the way, if you have dark and dark flat frames identically matched to the light/flat frames, you don't actually need bias frames.

The DeepSkyStacker website has a great overview:

http://deepskystacker.free.fr/english/theory.htm

[LightningNZ (Cam)]

I find somewhere around 20 dark frames to be pretty sufficient even with my noisy-as-all-hell Canon300D.

If you are flat-fielding using an LCD or EL panel rather than the sky, these are so bright (and your flats so short in exposure) that dark flats are quite unnecessary. Hard to do though with large apertures, or remote sites. I do consider it very important to get a large number of flats using this method though (at differing rotational angles and side-side translations) because of imperfections or smudges on the panels.

hope this helps,
Cam

[sil (Steve)]

Your list looks good. To be honest you can go a long way with just just lights though. Most of the hurdle is in processing techniques, teasing out those finer structures....just when you think your picture is looking good you see a tutorial that lets you take your image to a whole new level.

I've been doing photography for 20+yrs and when I got into digital I started taking lots of pics of the night sky just to muck about. So I only have lights for those times but I can still get some nice shots with what I know now about processing.

Also when it comes to flats/darks/bias I keep a well labelled set of master flats/darks/bias frames. Some of the characteristics these frames are meant to remove don't change much or at all over time with the same equipment. I've had success with improving old shots I only had lights for using the same gear/settings to put together a master dark/flat/bias. There are some differences of course which technically add noise but the improvements I still get outway the added negatives.

So I'd suggest as you go to keep a well labelled set of master dark/bias/flat frames for different combinations of lenses and settings. There will be times when the weather comes in and ruins a photoshoot before you can take darks etc but at least building up a set of masters gives you something you can fall back on if you need. Many people might just say to throw away the data and reshoot another night, but there are times when it can't be done that easily (comets/eclipses/holiday location). For me, having some data is better than no data.