Imaging Glossary Primer ?

[rabbithutch]

You folks who are imaging the skies amaze me. The things that you accomplish would have required whole governments of money when I was young.

In reading the various posts about imaging, I see many terms that I don't understand, and the glossary has not cleared any of the mystery for me.

Here are just a few terms that baffle me at this point:

sub

half

ha...

dark

flat

I've not found a primer on this topic but that can probably put down to my not knowing where to look and my general state of dullness.

TIA

[robbieince]

Sub = a sub exposure. Your images are made of several individual exposures, which you combine together to reduce noise. The individual exposures are called subs.

Half = not sure what context this is in but could mean exposing so that the signal is half the maximum ie when you take a flat it should be averaging at half saturation level.

Ha = hydrogen alpha emission frequency. The colour red associated with the light emitted by energetic hydrogen - used to detect signal not emitted by light pollution.

Dark = an exposure taken with the same temperature as your subs but with no light entering the recording system. Is used to capture the thermal and electronic noise in the recording system. Is subtracted from each sub.

Flat = an exposure through your recording system of a neutral target. It shows imperfections in your system such as uneven illumination (vignetting) or dust shadows. Is used to reduce these imperfections by dividing each sub (after dark subtraction) by the flat.

Hope that helps

Rob