|
The other two things you can reasonable do include:
1) stacking shots (Deepskystacker - freeware) take shorter duration shots and sum them up to make a better than equivalent longer shot (providing your target isn't so faint you are stacking only noise - not signal)
2) re-set your dark point higher (levelling) and boost / amplify the lumonsity difference between lighter and darker regions of the sky (non linear curves). Programs that do this are generally available - although I only know of expensive ones that do many other things - e.g. Photoshop CS2.
I'll expand on the second point a bit. Imagine sky glow causes a 10 minute shot to have 1 billion photos recieved per pixel in a dark area of the frame, whereas a real star that is faint boost the pixel it falls on to 1.2 billion photons and a bright star boost the photon on its pixels to 25 billion. All this data is recorded and sent to software that works out what to display - software that is generally written for day time use. You end up getting the image you see.
What you'd like to do is say any pixel lower than 1 billion photos - make it pitch black, and above 1 billion is a star, and if one is 25 times brighter - don't make it so bright the air around it glows and you get too much bloom swamping your picture.
So in a raw astro image you might get intensities of light that vary by a hundred million levels of intensity - you wish to throw away the junk and allocate what remains in a sensible way - that changes reality - by boosting very interesting faint details - like planetary nebulae e.g M42 Orion and toning down over bright areas - major stars. So for Orion the end effect might be altering the data of stars and glowing gases so instead of having a billion levels of light intensity between very bright and very faint objects - you end up with only 10,000 levels of light intensity.
You are cheating - boosting what you wish to see and dimming what would otherwise swamp shots. Welcome to astroimaging techniques!
Recommend reading the Zone System for Astrophotography by Rod Wodaski.
|