About 10 years ago I bought an 8" f/9 reflector. Or so I thought. '70s vintage Parks Optical aluminum tube. Great little scope.
Yesterday I pulled the mirror cell to clean the primary. Usually I just clean the mirror while in the cell but this time I wanted to replace the felt liner that cradles the mirror's edges as it had become worn and flat and no longer keeps the mirror from sliding around.
So I pulled the mirror out of the cell...
Lo and behold, hand written clear as day on the edge of the mirror, in big red letters, is "8" f/7 55 1/2" FL".
Hah! All these years I thought it was an f/9 and used that ratio in all my calculations!
I new there were extra holes toward the back end of the tube but I just thought someone in the past had moved the mirror up for some reason, imaging perhaps.
Now I have to go back and edit my notes.... .
Edited by Keith Rivich, 27 September 2020 - 11:41 AM.