I'm trying to mount an 80 mm refactor onto a dovetail plate (bottom of plate should be 2 15/16 inches wide). I have attached a picture below of the current mounting bracket (not sure exactly what it is called). I plan to take this off and put tube rings on it. I did not think it would be so difficult to find tube rings and a plate. Where can I find a good plate and compatible rings? I have found a few, but they are quite expensive. By the way, how necessary is it to have expensive (really good quality) rings for astrophotography?