|
RE DARK BACKGROUND
a common mistake in astro processing is people expect the sky to be black.... it isnt , logically if you consider even the hubble deep sky image there is many sources of light which your scope cannot resolve behind it.
The test is as follows, once you have callibrated your images (this means darks and flats for most people) you have an image which essentially contains all the light data, given you are using a DSLR and dont have to deal with the deep well issue of CD cameras, this is probably the point at which you will do your color balance. As described in my last post.
300 sec @ iso 400 should not give you a black sky IMHO . so from here have a look at IMAGES-ADJUSTMENTS-LEVELS there will be a histogram with 3 sliders underneath it, ( note when color balance is out you will often see a double hump, but at this point i assume you have done that), What you need to see is a bell shaped hump, check to see if there is a small tail to the left, this can be due to possibly alignment during stacking process , check edges of image to see that no black or underexposed area at edges exists if so crop out. it should only be couple of pixels wide.
Move the slider to the end of the tail if it still exists, you have now opened up your data to maximise its range.
IF YOU GO PAST THE TAIL AND INTO THE CURVE AS YOU HAVE ON YOUR POSTED IMAGE THEN YOU LOSE DATA, I CANNOT STRESS THIS ENOUGH.
the faintest detail exists at this end that is things like outer halos of galaxys .
At this point in your "career " it may not be obvious but as you progress it will be. your eyes are great , but the histogram NEVER lies.
hope this explains a few issues
a cheery regards
CLIVE
|