Thanks Steve, Luis and Doug. I am collecting data about 20km from Melbourne. Light pollution is a major pain.
This image was produced with the Canon 300mm F2.8 lens. I have been systematically eliminating all sources of 'noise'. This of course includes light pollution which leads to gradients.
Gradients are a major problem with wide fields. I think I am nearly there.
Here is the Carina Nebula showing dim dust and nebula detail without any sign of gradients. 12Mb
http://d1355990.i49.quadrahosting.co...R_newoptic.jpg
I have had this problem of colour casts due to vignetting and or colour shifts due to greater angles of incidence on the rear mounted LPR interference filter. See image of Rho region below.
By using an 82mm filter accurately mounted in front of the lens this has been eliminated.
By the use of a a lens hood that limits the area of sky the lens 'sees' to the actual image area, and stopping all light that does not contribute to the final image formation even entering the lens I think that I am minimising these problems.
In fact this even goes to flat correction as the flat is polluted by light rays that do not contribute to image formation.
I will try and write a more comprehensive story when I finally work out what is going on!
Bert
