Here are some Foucault shadowgrams of my 10 inch f/6 mirror using my
Foucault tester and my
Sony Mavica digital camera.
Each column shows the appearance of the full disk with the knife
positioned in the middle of the corresponding zone of the Couder screen.
Each row shows the results of
applying the action in the first column to the state in the previous row.
The numbers below each image are the deviations from the best sphere in thousanths of an inch as determined by the tester with the Couder screen.
The last column shows the profile the deviations of the right half of the mirror relative to a sphere (a cheapo integration of the deviation numbers); note scale changes.
(Click on an image for a 4x larger view. No image processing was
done beyond that done by the camera itself. You may notice some faint square patterns in the images;
these are digitization errors, not flaws in the mirror!)
|Zone 1||Zone 2||Zone 3||Zone 4||Error Profile|
|1/2 hour, tool on top (TOT), decentered 25%, pressure on outside edge|
|13 min, TOT, decentered pressure on zone 3|
|12 min, TOT, decentered pressure on zone 2|
|35 minutes, MOT, center-over-center strokes|
|20 minutes, MOT, long slow W-strokes, hands on edges|
|10 minutes, MOT, long slow W-strokes, hands on center|
|........... data below relative to a parabola ............|
|5 minutes, MOT, long slow W-strokes, hands on edge|
|6 minutes, MOT, long slow W-strokes, hands on edge|
|twice around (1 minute?), TOT, decenter slightly, light pressure on outside edge|
|twice around (1 minute?), TOT, decenter 50%, light pressure on outside edge|