I Decided to try and take some photos of the milky way and subtract dark frame from it (first time). However the more dark frames I subtract the greener the image got and nothing I did corrected this without making the photo in my opinion unusable. what am I doing wrong?
Stellaraya, Dark frames are used during the processing of stacked images in astro programs like Deep Sky Stacker which use them to eliminate hot pixels and the like.
Would help if you posted an image and explained better how you are trying to process your images. More information needed please.
Id post one if it wasn't like 2.5Mb in size, working on reducing it but for now.. I'm loading the Light frame into gimp then opening the dark frame as a layer then selecting Subtract in the mode and reducing opacity to about 50-60%. Using one frame makes it slightly green using two or more makes it a sickly green that is hard to correct.
Your dark subtraction is fine. The green cast is probably due to the milkyway being lower on the horizon. That's quite natural. There's a utility called Hasta la vista green (HLVG) which will remove green gradients from your pics. See repro attached.
Post Processing...
