[ATMoB-discuss] First photo from C14/ST7

[valleli at rcn.com]

Bruce, John


Another approach that John Martin used on the ST-5 was to put a 48-inch sq. sheet of clean, white poster board inside the roof of the McGregor Obs. and pointed the Schupmann at it while it was illuminated with incandescent lamps. 
This is not ideal because the diffuse reflection is not collimated. If it was, the doughnuts and defects from dust, etc. would have higher contrast in the flat.

Another way is to place a full-aperture sheet of opal glass in front of the corrector. This stuff is not easy to get ahold of.
It commonly was used to place under glass plates and negatives for direct viewing with uniform illumination under the opal.

John also placed two parallel sticks across the aperture as his focusing procedure. The diffraction is quite pronounced when inside or outside focus. Most disappears at correct focus.

Paul