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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.
A Beginners
Section.
Starter Kit for
newcomers who wish to begin Ronchi Testing.
Interpretation.
Basic Interpretation of Ronchi Patterns.
Software
Simulations and Analysis programs available for Download.
Scanning a surface while testing.
Diffraction
effects in a Ronchi Image.
Advanced
Interpretation
of Ronchi Patterns.
Interpretation
EXERCISES Will help you understand interpretation. Answers are below.
Interpretation
ANSWERS Print these out, fold over, to hide answers, then use in
conjunction with the exercises.
Test
variations and Set-ups.
Sources -
Light sources for Ronchi testing.
Gratings - A wide range of occulting Gratings.
Rigs
for a wide variety of Ronchi Tests.
Null Figuring using Ronchi Testing.
Advanced Setups for a wide variety of
applications of Ronchi Testing.
Aspherizing
using the Ronchi Test – methods and capabilities.
Capabilities
and Conclusions.
Conclusions and
Assessment of uses
and capabilities of Ronchi Testing.
History
and References
History of Ronchi Testing
References
and source material.
Background
I grew up
with Ronchi Testing, using other tests when necessary. This was in an era and place where few, if
any, materials were available specifically aimed at ATM’s.
This was a
mixed blessing. But one beneficial
result was independence from specialist suppliers combined with a readiness to
research, and try different solutions to problems. Local materials and
substitute methods were very important.
Some were a total failure. Some
worked reasonably. A few worked very well. We developed a system of Ronchi
testing that required no special tools [1]. There was nothing special in this because,
at that time, most ATM’s all over the world did the same.
Recently, I
have become aware that a younger, newer generation of budding ATM’s seems to be
at a disadvantage when compared to the older generation of ‘deprived’
ATM’s. Many seem to think special
equipment is needed for Ronchi-testing and that Roncigram interpretation requires
witchcraft. You can acquire or make special equipment later if you like, but,
when bombarded with information from the web, simply remember that :-
No special grating, nor special
measuring Rig, is required for normal Ronchi testing.
The ‘Web’
has bombarded younger ATM’s with a mixture of information and
disinformation. It is great that ideas
are so freely and quickly disseminated. Some are excellent but, because they
are not edited, others are less satisfactory, and a portion is simply devoted
to reinventing the wheel with the blind leading the blind.
For a
newcomer, I would recommend that purchasing a simple, but well written book,
may be less confusing and a more direct way to make a first telescope
mirror. This is paradoxical because
there is much truly excellent material on the web, but a newcomer will find it
extremely difficult to discriminate between the important and the trivial and
will likely become bogged down.
One should very quickly begin the
only activity that teaches the techniques – actual experience.
In a
society less tolerant to allowing experiments – a society which encourages
people to purchase items ready made – budding ATM’s may find them selves
directed by well meaning people to commercial resources that are expensive,
inappropriate, and often are unavailable in other countries or areas. If you look around, almost everything
required to make and test a telescope may be found commonly available. It is easy to become bogged down by well
meaning advice and never even start making a telescope mirror.
In this
environment I hope the following material will :-
1.
Provide
a means of assessing different methods of setting up for Ronchi Testing in the
only way that means anything – actual results.
2.
Question
if better results could be obtained with a much simpler test rig.
3.
Give
people in far-flung places the confidence to set up an excellent test with
simple local materials and not waste money on importing unnecessary items.
4.
Allow
users to instantly set up for Ronchi Testing without waiting for any special
materials.
5.
Help
newcomers and old hands alike to better evaluate Ronchigrams.
6.
Give
an interesting background.
7.
Be a
starting point for anyone researching Ronchi Testing material.
8.
Finally,
promote discussion of an interesting area of optics.
These are
ambitious aims. I hope they are at
least partially met. I did want to
extend and revise this material even further but other life matters must take
precedence.
I also hope that any disagreement with this
material prompts people to experiment in search of results and truths.
No doubt some of this will need to be rewritten
as better explanations come to mind.
(Peter Smith.)
NOTE.
All of the material is Copyright.
As long as material is used in unaltered form,
and is not sold for profit, I give permission for anyone to distribute and use
the material. This includes the
Programs RonchiZ and RonchiEstimates (see software)
which should also accompany this material.
Please note that a few of the photographs have been included by
permission of their owners. These have
been acknowledged.
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INDEX
[1] The local Astronomy club was
vigorous and used similar methods. On the
longer focal length reflectors we specialized in, the Ronchi test was
appropriate for prefiguring and even final figuring.