RONCHI INDEX

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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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[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