At the beginning of 2017 I decided to treat myself and order the telescope I had been craving since I began this hobby, the Skywatcher Quattro 200 CF. This carbon tubed f/4 Newtonian not only offered me a faster scope but also offered many other enhancements compared to my mid-90's Orion Europa 200.
Once it arrived and I got all of my accessories moved across to it I took some test shots and noticed a strange halo effect around bright stars....
This puzzled me, I had no idea what was causing it so I started this topic on Stargazers lounge. For the full story please read that topic but I will give the main points below.
Notice there are 3 areas, about 120 degrees apart, which are the locations of the mirror clips. The issue is caused by the polished edge of the mirror causing light to reflect in many directions, the images below show the edge reflecting looking down the OTA & also the silver edge of the mirror when the mirror cell was removed from the OTA.
There are a number of solutions to this problem:
- Paint the outer edge of the front face of the primary mirror using non-reflective dark paint to obscure the edge of the mirror.
- Add a ring of material, I chose self-adhesive flocking material, to obscure the edge of the mirror.
- Add some form of baffle to the inner edge of the tube to obscure the edge of the mirror.
The photo below show shows my flock ring fitted:
The difference this made was instantly observable, below is an image comparing the original problem (left) vs ring fitted (right).