James Vincent

Hi Mike

Good to hear the scope is coming along, for some reason i am unable to open up the pictures.

My scope is a 20 inch  F4.5 inch home made Dob based in the criege and Berry book.  The main mirror is home made, and it originally had an astro systems secondary mirror spider and heating system.The secondary mirror was changed because it was giving astigmatic images, mirror was not flat. It was replaced with a sky optics 30th wave and is now working properly.

Jim

One of the biggest issues with a Newtonian is way secondary mirror is attached to the holder, if it is bonded with silicon it can distort the mirror causing an astigmatic image.

The secondary should be quite thick at least 15 to 20mm for a 110mm  flat to prevent distortion.

hope you get it sorted out.

Jim