GOTO RONCHI INDEX
Copyright – P. J.
Smith
But permission is given to distribute this material in
unaltered form as long as it is not sold for profit.
BASIC TEST RIG
This test rig is similar to a simple Knife Edge
tester.
The main difference is a holder for the Ronchi
Grating, which is simply a commonly available 35 mm slide mount held with a
bulldog clip. This is versatile,
protects the grating, and is convenient if you wish to experiment and make many
quick changes.
By omitting the Slide mount the grating may be mounted
a little closer to the optical axis, but if this is important look at the
principle used in the Brute test rig.
The light source may be a small light bulb (preferably
the type with a built in lens) or a red LED.
The red LED, which is probably the best, is best
unmodified.
Simply drill a hole and push it in place.
In front of the light source must be a
ground surface of glass. A
small piece of thin glass ground on both sides is convenient. Microscope slide, window, or picture frame
glass is excellent. [1] See diffuser.
If you use a slit scribed on black painted glass, the
rear surface of the glass may be ground.
This then becomes the diffuser. See scribed
slit.
One easy way to hold the slit in place for experiments
is with blobs of BlueTac or modelling clay.
The 35 mm slide mount may be held with a small Bulldog
clip from the top. It is secure and
simple. If this is not too large, it is
easy to adjust the tilt of the grating with your fingers. An extension handle makes it more sensitive
but is not absolutely necessary. See the DeLuxe and Starter rig for a better
tilt adjustment.
The entire unit
should stand about 10 inches high and the cut-out on each side should be large
enough for your nose. A cut-out on each
side caters for both left and right hand viewers.
To use the unit in the Grating/Grating mode, simple
remove the slit and slide the grating partially over the light on the front of
the frame. A piece of ground
glass must be used between grating and light. You may need a spacer in front of the frame to keep the slide
mount from hitting the source. Examples
are found under the DeLuxe and Starter Rig.
For more delicate tilt adjustment (only needed in the Slit/Grating
mode), see the Deluxe Tilt rig.
If you need to get closer on axis, see the Close in
Brute Rig.
GOTO RONCHI INDEX