RONCHI

History

1938 – 1945

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.

More rational analysis,  a widening input

and new Serious Uses by Professionals

 

 

Towards the end of the 1930’s the Ronchi test had become well enough established and respected that it was used by some advanced amateurs and professionals for special advanced applications.

 

A few of these advanced amateurs were about to become skilled professionals.  The advent of WW2 precipitated a huge expansion of the optics industry world wide,  and personnel were required for advanced development of new equipment and routine production of items.  In countries with quite small optical industries, but with a pool of optical expertise in the Amateur field it was only natural for many to move into professional optics.  

 

This was to continue even after WW2 as the cold war developed and large US Avionics companies snapped up expertise from all over the world.

 

Examples are Cox (later to write regularly in Sky and Telescope), De Vany (later to work for Perkin Elmer and Hycon – the company which made the cameras for the U2 spy plane - finally he had a regular column in Applied Optics), Walard, and Lower.  In a similar way, many optical designers from areas as diverse as Germany and Wales subsequently surfaced in countries such as Switzerland ( eg. Bertele) and the US (eg. Herzeberger).  Funding, and being on the cutting edge of technology, has always been attractive to researchers, and they readily moved to less dangerous and more lucrative areas.

 

In many countries, ATMing activity and research was seriously disrupted by WW2, but activity continued at a reasonable level in the US.  Some basic research continued in Italy, although much was done in increasing isolation.

This was also true of other optical developments, for example, Holland (eg. Bouwers),  Russia (eg. Maksutov),  and France (Deve).

 

 

The following are mainly from the Scientific American columns edited by Albert Ingalls.

 

More often, some of the most significant developments were published in other prestigious scientific journals.  Scientific American often reported on extracts from these papers, but more and more the really serious ATM was searching for really up to date and more detailed information than appeared in Scientific American.  Much of the influence of Scientific American shifted to the published ATM books which were essentially reprints of earlier Scientific American material.  While extremely important, this precluded some of the more up to date information.

 

Scientific American magazine still remained an extremely important medium for dissemination information, so it is still a fruitful source of research material.  This was to continue yet for some time until the era of the more specialist publications such as Sky and Telescope which was in the near future.

 

 

 

1938. Ingalls, Scientific American, Jun 1938.  Ingalls reports on Kirkham’s use of a Ronchi grating when testing eyepieces. This is extended to quantitative measurements of Spherical aberration.

 

1939. Ingalls, Scientific American Apr 1939.  Ingalls refers to the recognition of amateurs such as H. A. Lower and Arthur De Vany by professionals.  Their pioneering work on Schmidt construction by Ronchi testing was behind this success.

 

1939 HW and LA Cox.  Journal of the British Astronomical Society. 50, 61-68, (1939).  Placed a slit at the focus of a Schmidt and observed the image by eye through the front.  He used a straight edge to aid interpretation and points out that this is essentially the same as a method used by De Vany which used a square grid at the focus of the Schmidt. 

 

1939. R. Platzeck and E. Gaviola. JOSA. 29, 484, (1939)   "On the Errors of Testing and a New Method of Surveying optical Surface and Systems".  While this has nothing to do with Ronchi testing, it does indicate the push for new more rigorous testing methods.

 

1939. Ingalls, Scientific American Aug 1939. Ingalls reports on testing correcting plates.  Uses light beam on a small silvered glass bead as pinhole.

 

1940. Ingalls, Scientific American, Dec 1940. Ingalls reports on people relying on estimating shadows without zonal testing – resulting in poor mirrors.

 

1941. Ingalls, Scientific American, Jan 1941. Ingalls reports on testing a Wright corrector.

 

1941. Ingalls, Scientific American, Aug 1941. Ingalls reports on the difference between professionals and amateurs. One tests at Centre of curvature, the other at focus using some null test. Each considers the other peculiar.

 

1941. Ingalls, Scientific American, Aug, 1941. Ingalls reports of a description by Eugene G. Brown of the Detroit Astronomical Society of a reflection null for extremely short mirrors which is now often called the Waineo Null test. Brown adds that Ralph Tozer of Detroit is the first there who used the test described above.

Below is a diagram.  The light is piped in via a Perspex (Lucite) rod.  Being a null test, Ronchi lines should appear straight.  In a similar way, the light pipe may supply light to a pinhole.  Today, small LED or Laser Diode sources make this less important.  A variation is to use an extremely fine fibre optic strand.  The end may be small enough to act as a pinhole without any attention or a glass ball may be formed by melting the end.  This assures more even illumination.

 

1941. Ingalls, Scientific American, Aug, 1941. Ingalls reports C. M. Davenport and W. S. Bohlman uses piped-in light for testing both as a pinhole and ronchi source.

 

1942. 1942. Ingalls, Scientific American, March 1942.  Ingalls reports on Dr. Struve’s use of a Ronchigram for confirmation of progress in parabolizing very large observatory mirrors.

 

1942. Ingalls, Scientific American Apr, 1942.  Ingalls reports of the superb quality of the 82" mirror of the McDonald Observatory.  The Ronchi test was one of many used.

 

1942. Ingalls, Scientific American, May 1942.  Ingalls reports on testing a large corrector plate and the movement of amateurs into the ranks of professionals such as Cox and McGuire.

 

1943. Ingalls, Scientific American, Jun 1942.  Ingalls reports the use of a mercury sphere as source during testing.  Microscopists had commonly used this as a testing source.  This technique was occasionally used by some pioneers of testing nearly a century beforehand.

 

1943. Ingalls, Scientific American, Aug 1943.  Ingalls reports on testing for turned down edge comparing sensitivity of the Ronchi test.

 

1944. Ingalls, Scientific American, May 1944.  Ingalls reports on concave grating mirrors used in a Fabry- Pérot interferometer which were supposedly shown to be accurate to 1/50 wavelength by a Ronchigram.  Some of these optics were for Neils Bohr. Ingalls implies that 1/50 wavelength accuracy is possible of the test.  This is quite tenuous and shows some lack of understanding and rigour on his part.

 

 

Other Developments

 

 

 

 

1938. R. Crino. Ottica. 3, 304, (1938)

 

1938. R. Calamai. Ottica. 3, 41, (1938)

 

1938. R. L. Wallard. J. Sci. Instr. 15, 339, (1938)  Made a Schmidt using a Slit at the focus as a source which was re-imaged via a refractor through a Ronchi Grid made of 120 wires per inch.  This is especially about examining an unpolished surface smeared with oil.  He went on to make a 30/36 inch Schmidt for St. Andrews University, Scotland. Some testing was via an oil flat in autocollimation when he used Grating/Grating.

 

Kirkham and others had earlier combined a viewing telescope which received parallel light from an optik under test.

One part of the system contained the slit, the other the grating.  Wallard applied this to the figuring of the corrector plate of a Schmidt correcting plate.

 

He also further developed an autocollimation test using oil for the flat reflecting surface for both Newton and Cassegrain variants..  Since there were many reflections from unsilvered surfaces, he chose to use the grating/grating mode for maximum light throughput.

 

                  

 

 

The above diagrams also show how he used a remote viewing telescope to access the focal region.

 

 

1938 John Strong.  "Proceedings in Experimental Physics", p 77 - 78   Uses both Grating/Grating and Slit/Grating variations depending on the optics under test.  This excellent publication, a Laboratory Manual, helped to spread knowledge about Ronchi Testing. Unfortunately, some of the Ronchigrams in some editions of this book have been transposed and are incorrect.  The following is an example.

 

 

 

1938. HW and LA Cox.  Journal of the British Astronomicaql Society. 48, 308-313, (1938)   "The Construction of a Schmidt Camera".    This describes construction of a Schmidt camera.  Used a Slit and a Grating.

 

 

This is often called the Lower test.

 

 

 

1939 HW and LA Cox.  Journal of the British Astronomical Society. 50, 61-68, (1939)  Placed a slit at the focus of a Schmidt and observed the image by eye through the front.  He used a straight edge to aid interpretation and points out that this is essentially the same as a method used by De Vany which used a square grid at the focus of the Schmidt. 

 

1939. R. Platzeck and E. Gaviola. JOSA. 29, 484, (1939)   "On the Errors of Testing and a New Method of Surveying optical Surface and Systems"

 

1939. Di. Jorio. Ottica. 4, 31, (1939)  Further developed physical model.

 

1939. Di. Jorio. Ottica. 4, 83, (1939) Further developed physical model.

 

1939. E. Ricci. Ottica. 4, 104, (1939)

 

1939. B. Crino. Ottica. 4, 114, (1939)

 

1939. Di. Jorio. Ottica. 4, 184, (1939) Further developed physical model.

 

1939. R. Bruscaglioni. Ottica. 4, 204, (1939) Investigation of the sensitivity of the test.

 

1939. Di. Jorio. Ottica. 4, 254, (1939) Further developed physical model.

 

1940. G. Bocchino. Ottica. 5, 219, (1940).  Did research on 5th order spherical aberration.

 

1940. V. Ronchi. Ottica. 5, 275, (1940)

 

1940. G. Bocchino. Ottica. 5, 286, (1940) Did research on 5th order spherical aberration.

 

1940. V. Ronchi. Lezioni di Ottica Ondulatoria (Zanichelli, Bologna), (1940) Investigation of the sensitivity of the test.

 

1941. P. Pallitino. Ottica. 6, 26, (1941) Further developed physical model.

 

1941. G. Toraldo di Francia. Ottica. 6, 151, (1941)  Development and comparison of Geometric and Physical models. He developed exact shape of fringes with wave theory.

 

1941. G. Toraldo di Francia. Ottica. 6, 258, (1941) Development and comparison of Geometric and Physical models. He developed exact shape of fringes with wave theory.

 

1942. Di. Jorio. Ottica. 7, 243, (1942) Further developed physical model. He developed exact shape of fringes with wave theory.

 

1942. G. Toraldo di Francia. Ottica. 7, 282, (1942) Further developed physical model. He developed exact shape of fringes with wave theory

 

1942. G. Toraldo di Francia. Ottica. 7, 304, (1942)  Attempts to apply to chromatic aberration measurement.

 

1942. Di. Jorio. Ottica. 7, 314, (1942)

 

1943. G. Toraldo di Francia. Ottica. 8, 1, (1943) Further developed physical model. He developed exact shape of fringes with wave theory.

 

1943. Di. Jorio. Ottica. 8, 92, (1943)  .

 

1943. G. Toraldo di Francia. Ottica. 8, 225, (1943)  Further developed physical model. He developed exact shape of fringes with wave theory.

 

1943. Di. Jorio. Ottica. 8, 288, (1943) Further developed physical model.

 

1943. G. Bocchino. Ottica. 8, 310, (1943)

 

1947. G. Toraldo di Francia. Atti. Fond. G. Ronchi 2, 25, (1947)  Further developed physical model. He developed exact shape of fringes with wave theory.

 

1947. G. Toraldo di Francia. Atti. Fond. G. Ronchi 2, 89, (1947)

 

1948. L. G. Schulz. JOSA. 38, 432, (1948)  The name Ronchigrams was coined by Schulz.  Application to aspherics.



 

GOTO   RONCHI   INDEX