3.25" (82mm) Helios Solar Film Filter. Fits Optical Tube Diameter 2 7/8" (74mm) to 3 1/8" (79mm)

hey guys quit the lazy geek here today I want to talk about a little problem that I had are a little trick I found about basically preserving back focus in my systems when I want to input when I want to include like two inch filters in there back focus is basically while it can mean a lot of things but in my in this particular case it's the distance that you want to have between a lens or a telescope and the camera sensor so here is a lens that I have which is a sigma lens for canon and the canon system specifies that between the OS mount flange and the camera sensor we should have exactly forty four millimeters and i have an adapter that i use from astro mechanics that's 19 millimeters in thickness so it takes up a lot of those almost half of these 44 millimeters already and on top of that adapter which goes to m42 threads here i want to use a two inch CLS ccd filtered I have from up t