The Single Wire Test
There are two aspects to this arrangement that are of especial interest
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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.
The effects of diffraction are different
The edges of the wire show a diffraction effect
but the edge of the mirror has no multiple image.
More
photographs of Single Wire test images as applied to a Sphere will be found
under Scanning across the Ronchigram.
Very deep Aspherics may be tested
My program RonchiNu simulates this
test.
When very deep Aspherics are tested with a single wire a well defined
ring is seen when outside Centre of Curvature.
By measuring and comparing this ring with predicted shadows at definite
wire positions, the curve may be checked for different zones.
This is what most define as the ‘Wire Test’. It is particularly useful for very deep Aspherics. It has been reported by Cox in Sky and
Telescope, De Vany, and Malacara.
More recently, some are using a technique that scans a wire across a
mirror. The measured scan is matched
with settings against a notched pinstick across the mirror. It is placed inside COC. This is of more use with shallower mirrors.
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