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Ronchi Gratings

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Posted by Robert May on October 31, 2002 21:07:00 UTC

You don't need a Ronchi Grating for making a Foucault tester. You just need a razor blade for the purpose.
You may want to stop by my website where, on one of the subpages in the mirrormaking article, testers are commented on.
http://bobmay.astronomy.net .
Ronchi gratings are available from a number of places from Edmund Scientific to Willmann-Bell amongst others.
One of the early methods of making a grating was to take fine copper wire and wrap two strands between two copper or brass rods in a frame and remove one strand of the wire and then solder the other wire to the rods. Then remove the second side of the wires and use this as a grating. The spacing will be that of the wire size. The better way now is to print or etch the lines on a piece of glass or plastic or make a photograph with fine quality B&W film, depending upon the desired size of the spacings.
If you desire to make gratings with film, make sure that you get the spacing even and the lines 50% wide.
People have done gratings with printers but often have problems with uneven spacing due to the software that is normally used interpolating the spacing and putting down 10 dots on one line and 11 dots on another line, making the grating useless for optical work.

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