Describes various test rigs which are easy and cheap to build.
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Copyright – P. J.
Smith
But permission is given
to distribute this material in unaltered form as long as it is not sold for
profit.
NOTE
A range of possible Ronchi test rigs is
presented. A huge number of approaches
are possible and anyone with a minimum of supplies can successfully implement this
test.
Beginners are best served by initially constructing
one of the simple types. I suggest
either the Starter Kit Rig or Basic Rig with the Deluxe option added later.
Since measured movements of the Ronchi grating is
unnecessary for normal Ronchi testing, none of the following include this
feature. [1] Of course, you can use a precisely
controlled Zonal Foucault Tester with calibrated slide for Ronchi testing if
one is available.
Starter Rig is
suggested as a quick way to begin if you are using a professional grating.
Basic Rig works
well. It is quick to make and
versatile.
Deluxe Rig is simply
the Basic rig with fine tilt adjustment of the slit. It is versatile and highly recommended.
The Brute is a
high wattage rig for multiple surfaces working extremely close to the
axis. Crude but effective.
Simple Rig is
mobile and uses a flashlight and aluminium extrusion. Best for rough testing.
Emergency Rig
improvised from a small flashlight.
Laser Diode Rig
uses the point source of a Laser Diode.
Easy to set up but not normally recommended.
Crude Mirror Stand
with simple tilt adjustment is a necessity.
Avoids broken mirrors !
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[1] Some people combine measured longitudinal grating displacement with Ronchi testing when attempting to estimate the degree of asphericity. This is of course unnecessary when testing Spheres. See under Aspherizing for more details.