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.
Immediately after the announcement by Ronchi of the
Grating test there was a flurry of activity both by Ronchi’s close associates
and others, mainly in France and Germany.
It would seem that little, if anything, appeared in English publications
in this period.
Ronchi was determined to explain the Grating test in
terms of Wave optics and saw it as an interesting piece of pure science more
than something to be applied in production work. Others immediately saw the test as a practical solution to
optical production and testing and they neither understood fully nor cared much
about anything other than an explanation in geometric terms.
Ronchi [1]
himself says “A period of evolution
of these ideas followed, and the fact that, in the meantime in other centres of
optics, gratings were being employed in testing optical systems also
contributed to this process. The most
interesting cases were those of Lenouve l[2]
and of Schulz. Schulz’s publication [3],
however, did not appear until 1928. We
mention these cases because it must be stated that they really did not speak of
gratings, in the meaning of instruments functioning by diffraction; Lenouvel,
instead of speaking of ‘resaux’, speaks of ‘trames’, and Schulz refers to
‘Rastern’ instead of ‘Gitter’. This
philosophical remark is sufficient to demonstrate that these authors were also
only interested in gratings ‘at low frequency’, therefore, there was no need to
refer to interferential considerations, but the strictly geometrical study of
their behaviour was sufficient. These
authors explicitly limited themselves to gratings of not more than 10
lines/mm.”
“Particularly interesting was the publication of Yvon [4] who, by taking
the geometrical reasoning too seriously, reached unfavourable conclusions on
the employment of gratings as a means of study of optical systems.”
“As long as the grating employed had a very low
frequency, like the ones we had used at first and that also had been used by
other authors treating the same argument, the geometrical reasoning
corresponded quite well with the results of the experiments and measurements;
but at the same time the method did not lead to results as fine as desired. It was evident that in order to increase this
sensitivity it would be necessary to use gratings of the highest frequency
possible, but then the results decidedly deviated from those predicted from
geometrical reasoning.”
In retrospect, both Ronchi’s obsession with fitting
the test to wave optics and his contemporaries’ obsession with immediately
applying the test to production using geometrical theory were limiting. If the theory and computing power had been
available, the test would have had a huge impact on testing with low frequency
gratings even without wave theory. Yet,
it is true that a full understanding could never have occurred without
understanding wave optics.
We should consider the state of testing at this
stage. Test plates and Newtons rings
were well understood, The Fizeau interferometer had been in use for 50 years,
and the Adam Hilger made and patented Twyman Green interferometer, an outgrowth
of Michelson’s interferometer but dedicated to testing, was just finding its
way into the best establishments such as Zeiss. The Ronchi test gave ‘fringes’ similar in some respects to these
other interferometers so it is perfectly understandable that some of the
research activity into the Ronchi test was aimed at widening the range of
similar testing methods.
We now know that the Ronchi fringe pattern is actually
a shearing Interferometer. These were not really analysed until the 1950’s and
1960’s when their more complex fringe pattern was properly understood. But in the 1920’s the research and analysis
had yet to be done which would allow of easy interpretation of the Ronchi
Fringe pattern.
This was way before any other type of shearing
interferometer and the shapes of the fringes in the presence of spherical
aberration was new.
While Ronchi was a little disparaging of over zealous
geometrical interpretations of these fringe shapes, we now know that a rigorous
geometrical analysis would have explained these fringe shapes.
Hence a potentially useful and simple test languished
– waiting for a slow but steady effort to untangle the fringe patterns.
It was not until Anderson and Porter demonstrated the
usefulness of the Ronchi Test in 1929 that the test gained a new leash of life both
in large telescope optics and the vibrant ATM movement nurtured by Ingall’s
Scientific American columns. Ronchi
himself says “Numerous amateur
astronomers were of the same opinion, especially in the United States, and they
have long considered the grating test the most suitable for their
constructions, also because it does not require equipment either expensive or
difficult to obtain. It must also be remarked that by 1938 Waland had pointed
out the practicability of the achromatic grating interferometer for testing
aspherical surfaces while being manufactured.
The same was demonstrated by Schulz in 1948; indeed Schulz had the
courtesy to coin the name ‘Ronchigrams’ to indicate the figures of shadow
fringes. In 1959, two Australian
astronomers, Sherwood and Lumley, published indications to simplify the
appliance of the grating interferometer in the construction of surfaces with parabolic sections, as those
utilized in astronomical mirrors.”
But we are getting ahead of ourselves. The next historical section will consider
the era from 1929 – 1938 in more detail.
References
Published in during this Era
1924. L. Lenouvel. Rev. Opt. 3, 211, (1924)
1925. V. Ronchi. La Prova dei Sistemi Ottici
(Zanichelli, Bologna, (1925)
1925. V. Ronchi. Nuovo Cimento 2, 1, (1925)
1925. V. Ronchi. Nuovo Cimento 2, 517, (1925)
1925. V. Ronchi. Rend. Accad. Naz. Lincei. 1, 659,
(1925)
1925. V. Ronchi. Rend. Accad. Naz. Lincei. 2, 257,
(1925)
1925. V. Ronchi. Rend. Accad. Naz. Lincei. 2, 319,
(1925)
1925. L. Lenouvel. Rev. Opt. 4, 294, (1925)
1925. L. Lenouvel. Rev. Opt. 4, 299, (1925)
1925, G. Yvon. Rev. Opt. 4, 353, (1925)
1926. V. Ronchi. Rend. Accad. Naz. Lincei. 3, 680,
(1926)
1926. V. Ronchi. Rend. Accad. Naz. Lincei. 1, 569, (1926)
1926. V. Ronchi. Z. Physik. 37, 732, (1926)
1926. V. Ronchi. Rev. Opt. 5, 441, (1926)
1926. V. Ronchi. Z. Instrumentenk. 46, 553, (1926)
1926. C. V. Raman and S. K. Datta. Trans. Opt. Soc.
27, 51, (1926)
1927. G. B. Pacella. Rend. Accad. Naz. Lincei. 5, 752,
(1927)
1927. V. Ronchi. Nuovo Cimento. 4, 297, (1927)
1927. V. Ronchi. Nuovo Cimento. 4, 343, (1927)
1928. J. Jentzsch, Phys. Z. 24, 66, (1928) "Die Rastermethode, ein Verfahren zur
Demonstration und Messubg der Spharischen Aberration".
1928. G. Schulz. Annal. Physik. 35, 189, (1928)
1928. V. Ronchi. Rev. Opt. 7, 49, (1928)
1928. V. Ronchi. Z. Physik. 46, 594, (1928)
1928. V. Ronchi. Lezioni di Ottica Fisica (Zanichelli,
Bologna), (1928)
1929. J. A. Anderson and R.W Porter, Astrophys. J. 70,
175, 175, (1929) "Ronchi's
Method of Optical Testing"
GOTO RONCHI INDEX
[1] 1964 V. Ronchi. Appl. Opt. 3, 437, (1964). "Forty Years of History of a Grating
Interferometer"
[2] 1924 L. Lenouvel. Rev. Opt. 3, 211, (1924)
1925 L. Lenouvel. Rev. Opt. 4, 294, (1925)
1925 L. Lenouvel. Rev. Opt. 4, 299, (1925)
[3] 1928 G. Schulz. Annal. Physik. 35, 189, (1928)
[4] 1925, G. Yvon. Rev. Opt. 4, 353, (1925)