Optics in Italy Adriana Fiorentini A brief review is presented of the work carried out in Italy in various branches of optics and related fields. Introduction Modern optics developed in Italy in the early 19th century, mainly in regard to theory and the construc- tion of optical instruments. Most of the earlier opticists in Italy were astronomers; a few others pioneered in the design of optical instruments for topographical purposes. Optical research was active around 1850, the period of Amici, Porro, and Ricc6, but it gradually de- clined until, in the years preceding 1914, neither scientist nor organization contributed to the develop- ment of optics in Italy other than those optical in- dustries founded at the end of the 19th century. The first organization devoted to optical research, the Laboratorio di Ottica e Meccanica di Precisione, founded in 1917, operated no more than a few years. Only personal contributions to optical research, outside any organized scientific body, were made in the following decade until a new organization, the Istituto Nazionale di Ottica, became active in 1927. This Institute was created for the purpose of promoting the development of Italian optical research and providing advanced instruction in the various branches of optics. It is still the only organization exclusively devoted to the study of optics in this country, although several other organizations contribute in part to the development of particular branches of optics: the research laboratories of the optical industries, the Physics Departments of some universities, the Center for the Study of Micro- wave Physics of the National Research Council and, for physiological optics, the Departments of Ophthal- mology, Physiology, or Psychology of some universities. The following sections contain a brief review of the work carried out in Italy in specific fields of optics. The author is at the Istituto Nazionale di Ottica, Firenze, Italy. Received 26 January 1962. This review should in no way be considered as com- plete; it will only point out some of the highlights of optical development in Italy. In particular it does not consider research applicable to solid-state physics rather than to optics in the strict sense. For more de- tailed information on the subjects mentioned in this paper the reader will be referred to the original publica- tions. 1. Geometrical Optics and Optical Design A number of Italian scientists have contributed to the development of the theory of optical instruments since the early 19th century. Among them are Amici and Porro, whose works are so well known that they do not require to be mentioned here, and a few others, lesser known, such as Mossotti who, in his book on the theory of optical instruments,' presented a complete treatment of third-order aberrations and who first demonstrated the possibility of correcting both the spherical and sine aberrations of a cemented doublet (by the formula found later by Harting); Billottil who studied trigonometrical ray tracing; and Ferraris who considered the cardinal properties of optical sys- tems. More recently, geometrical optics and optical design have perhaps not been so generally cultivated in Italy as in other countries, although research of con- siderable interest was carried out during the period following World War II and in the last few years. The design of a new Schmidt telescope, having only spherical surfaces, is due to Colacevich' who also con- tributed to the study of optical concentric systems 4 and proposed a new formula for the interpolation of the refraction index of glass.' Early studies on aspherical refracting surfaces were performed by Scandone.A Various papers by Toraldo di Francia deal with the correction or the calculation of some aberrations of particular optical systems 7 8 and with the variation of axial aberrations as a function of object distance.' Recently Cambi has developed a projective formula- May 1962 / Vol. 1, No. 3 / APPLIED OPTICS 279
Transcript
Optics in Italy
Adriana Fiorentini
A brief review is presented of the work carried out in Italy in various branches of optics and relatedfields.
Introduction
Modern optics developed in Italy in the early 19thcentury, mainly in regard to theory and the construc-tion of optical instruments. Most of the earlier opticistsin Italy were astronomers; a few others pioneered inthe design of optical instruments for topographicalpurposes.
Optical research was active around 1850, the periodof Amici, Porro, and Ricc6, but it gradually de-clined until, in the years preceding 1914, neitherscientist nor organization contributed to the develop-ment of optics in Italy other than those optical in-dustries founded at the end of the 19th century. Thefirst organization devoted to optical research, theLaboratorio di Ottica e Meccanica di Precisione, foundedin 1917, operated no more than a few years. Onlypersonal contributions to optical research, outside anyorganized scientific body, were made in the followingdecade until a new organization, the Istituto Nazionaledi Ottica, became active in 1927. This Institute wascreated for the purpose of promoting the developmentof Italian optical research and providing advancedinstruction in the various branches of optics. It isstill the only organization exclusively devoted to thestudy of optics in this country, although several otherorganizations contribute in part to the development ofparticular branches of optics: the research laboratoriesof the optical industries, the Physics Departments ofsome universities, the Center for the Study of Micro-wave Physics of the National Research Council and,for physiological optics, the Departments of Ophthal-mology, Physiology, or Psychology of some universities.
The following sections contain a brief review of thework carried out in Italy in specific fields of optics.
The author is at the Istituto Nazionale di Ottica, Firenze,Italy.
Received 26 January 1962.
This review should in no way be considered as com-plete; it will only point out some of the highlights ofoptical development in Italy. In particular it does notconsider research applicable to solid-state physicsrather than to optics in the strict sense. For more de-tailed information on the subjects mentioned in thispaper the reader will be referred to the original publica-tions.
1. Geometrical Optics and Optical Design
A number of Italian scientists have contributed tothe development of the theory of optical instrumentssince the early 19th century. Among them are Amiciand Porro, whose works are so well known that they donot require to be mentioned here, and a few others,lesser known, such as Mossotti who, in his book on thetheory of optical instruments,' presented a completetreatment of third-order aberrations and who firstdemonstrated the possibility of correcting both thespherical and sine aberrations of a cemented doublet(by the formula found later by Harting); Billottilwho studied trigonometrical ray tracing; and Ferrariswho considered the cardinal properties of optical sys-tems. More recently, geometrical optics and opticaldesign have perhaps not been so generally cultivatedin Italy as in other countries, although research of con-siderable interest was carried out during the periodfollowing World War II and in the last few years.
The design of a new Schmidt telescope, having onlyspherical surfaces, is due to Colacevich' who also con-tributed to the study of optical concentric systems4and proposed a new formula for the interpolation of therefraction index of glass.' Early studies on asphericalrefracting surfaces were performed by Scandone.AVarious papers by Toraldo di Francia deal with thecorrection or the calculation of some aberrations ofparticular optical systems7 8 and with the variation ofaxial aberrations as a function of object distance.'Recently Cambi has developed a projective formula-
May 1962 / Vol. 1, No. 3 / APPLIED OPTICS 279
tion of the problems of geometrical optics with an ap-plication to the design of a centered optical system.' 0
Substantial contributions to geometrical optics andoptical design have been made by Morais. Besidesvarious types of photographic lenses, range finders,and periscopes, Morais has designed wide-angle lensesfor aerial photography (unpublished report), a par-ticular photographic lens with a distortion not greaterthan 1 t over a 30° field (to be applied to a bubblechamber), and a solar telescope." He has also contri-buted to the study of concentric systems' 2 and to thestudy of high-order aberrations,'" has applied vectorhomographies to the design of optical systems, 1
4 and hasderived a generalized formulation of Heath's law. 1Many other papers by the same author deal with theparticular problems of anamorphic systems, systemswith variable focal length, etc.
Other contributions to optical design are mentionedin Section III.
II. Diffraction
The chief contributor to the study of optical dif-fraction has been Toraldo di Francia. In a number ofpapers he developed a new formulation of the funda-mental problems of diffraction through the principleof inverse interference, postulated and demonstratedthe existence of evanescent waves in diffraction, gave asatisfactory account for the anomalous propagation of
waves, applied the Gibbs phenomenon to the theoryof optical images and to contrast-phase microscopy,demonstrated that diffraction is not in general a revers-ible phenomenon in the thermodynamic sense, etc.Most of his earlier contributions to the development ofdiffraction theory are contained in his recent volume"La diffrazione della luce,""1 a general introduction tolight diffraction from the point of view of modern ap-plications.
Toraldo has also shown the advantage of consider-ing a third branch of optics, intermediate between geo-metrical optics and wave optics but having character-istic features of its own, which he called parageomnetricaloptics.'7 Parageometrical optics has proved to be avaluable means of investigation in the field of micro-waves.
A contribution of primary importance in the under-standing of fundamental diffraction phenomena is alsodue to Toraldo di Francia, who demonstrated thatno theoretical limit exists for the resolving power ofan optical system." This fact has been shown to bea necessary consequence of the role of evanescent wavesin diffraction. The same author has also computedsuitable amplitude and phase distributions on the pupilgiving resolving powers much higher than the classicalone. 19
Some properties of diffraction gratings have beeninvestigated by Ronchi, Scandone, Toraldo di Francia,
and others. Some of this work is mentioned in the nextsection.
Ill. Applied Optics
Passing in rapid review the many topics pertainingto applied optics we shall first refer to the so-calledgrating-interferometer devised by Ronchi2 0 whosetheory and application have been widely treated inItaly. Soon after its conception, the grating-inter-ferometer proved to be a successful means of progress,partly because of its interesting theoretical implica-tions but also because of its practical use, a direct con-sequence of the simplicity of its application to testingoptical instruments. A great deal of work was thendevoted to the development of the Ronchi test; themain contributors have been Di Jorio, 2' Bocchino,22
Bruscaglioni,2 3 Scandone,24 and Toraldo di Francia.2 'The exact theory of the grating-interferometer waslater developed in a simple and elegant manner byToraldo di Francia.26
In the field of optical instruments for astronomicalpurposes, mention should be made of several spectro-graphs designed and constructed in Italy which, if notcompletely original, at least present considerable im-provements over the classical types. The solar spectro-graph designed by Morais" and mounted at the Astro-physical Observatory of Arcetri is a modification of theclassical Eagle type where the single mirror has beenreplaced by a Cassegrain-system with the advantage ofa greater compactness of the whole instrument. Fra-castoro has made use of a perforated grating in thedesign of a spectrograph to be applied to the Zeissreflector telescope of the Lojano Observatory.2 7 Ahigh luminosity mirror spectrograph, whose opticalsystem has been designed by Morais, presents a par-ticular solution of the problems of flexures and ofthermal isolation, due to Guidarelli.2 ' The instru-ment contains a Cassegrain collimating system and acamera which consists of a catadioptric concentricsystem.
Considerable advance has been made recently in thedesign of optical instruments for topographical purposes,a field of research to which Italian researchers havedevoted constant attention ever since the days ofPorro. A high-precision automatic level has beenrecently conceived and constructed29 which permitsleveling operations with the accuracy of the order of1 see of arc.
Optical applications to photogrammetry are alsobeing developed. Wide-angle objectives for aerialphotography with very small distortion have beendesigned and the distortion measured by a new in-strument.3 0 Stereocomparators of extremely high ac-curacy have also been built. 3
Some contributions have been made to the study ofphotographic emulsions as regards their performance
280 APPLIED OPTICS / Vol. 1, No. 3 / May 1962
as receptors of optical images. The resolving powerof photographic materials was measured independentlyfrom that of the objective lens by a resolvimeter de-signed by Bruscaglioni,3 2 and measurements in avariety of experimental conditions were carried out byBocchino.33 Fracastoro also contributed to the theo-retical and experimental investigation of somecharacteristics of photographic emulsions.3 4
IV. Physiological Optics
The study of vision is spread over a number of fieldsin both the physical and biological sciences; con-sequently it is difficult to make a comprehensive reviewof the work done in this field. An attempt will be madeto mention at least the main sources of information.
A group of research workers at the Istituto Nazio-nale di Ottica has been working in the field of visionfor the last ten years. Most of them are physicists andhave investigated mainly the physical and psycho-physical aspects of vision. In addition, electro-physiological and psychological phenomena connectedwith vision have been widely investigated.
Toraldo di Francia has emphasized the need forusing wave optics instead of geometrical optics whendealing with the performance of retinal receptors.The analogy between retinal cones and microwaveantennas suggested in particular a new interpretationof the Stiles-Crawford effect.35 36 Toraldo has alsopointed out the role of spacial and temporal gradientsof retinal illumination in affecting visual response,starting a number of researches which have been car-ried on by his co-workers. Investigations by LuciaRonchi and her collaborators cover a variety of sub-jects, namely, the readability of printed characters ofvarious shapes,3 7 the effect of mydriatics on some visualfunctions,38 the directivity of retinal receptors,36 theeffects of possible rod-cone interaction at mesopiclevels,39 -47 ' the speed of reading under critical con-ditions,4 2 -4 4 the effects produced by figures with quasi-perceptive contours,45 etc. A great deal of work hasalso been done by Lucia Ronchi and her co-workers onthe electroretinographic response to various types oftime-varying stimuli46 -4 8 as well as on the possible in-teractions between electrical responses to stimuli ofdifferent wavelengths. 4950
V. Ronchi is responsible for a number of papers onsome psychological aspects of vision, and his con-tributions to this field are summarized in a recentvolume.'" The author of the present review and herco-workers have contributed to the study of contour-contrast effects,' 2 -"5 of some dynamic characteristicsof vision,'6 and of binocular interaction.' 7
Most of the Italian contributions to the study of thephysiology of the eye have been made by groups ofworkers in the Ophthalmological or Physiological De-
partments of certain universities. Mention may bemade, for instance, of the investigations on the elec-trical response of the eye made by Wirth at the Oph-thalmological Department of the University of Rome,'8
of a number of researches carried out at the Universityof Pisa by Focosi and his co-workers,' 9 6 ' especially inthe field of binocular vision, and of some investigationson the electroencephalographic response of variousanimals connected with visual stimulation, made underthe direction of Moruzzi at the Neurophysiology De-partment of the University of Pisa.66-6 '
Psychological aspects of vision have been investigatedat the Catholic University of Milan and at the Psy-chology Departments of the University of Florence,Rome, Palermo, etc.
V. Related Fields
In Italy, as anywhere else, considerable advance hasbeen recently made in some fields of research which, ifstrictly speaking do not belong to optics, are at leastrelated to it, either because their development hascontributed to a new formulation of classical opticalproblems or because the problems they raise can besolved by methods very similar to those applied in con-ventional optics.
One of these fields is that of microwave physics.At the Centro Microonde C.N.R. in Florence, a groupperforming research in optical microwave systems hasbeen constituted under the direction of Toraldo diFrancia. The researches carried out by this group inthe last few years have covered a variety of subjects.The methods of optical design have been successfullyapplied in the study of configuration lenses for wide-angle and high-speed scanning.
New types of perfect configuration lenses have beenfound and correction of spherical aberration of verysimple microwave lenses have been obtained by lenscombinations quite similar to optical doublets.6 9 7
Concentric stigmatic systems of the Luneberg typehave been widely investigated; the mathematical prob-lem of finding all possible lenses of this type has beensolved,7 2 and a particular class of lenses has been de-scribed.73 74 Some of these systems, having an outerspherical shell of constant index and an inner core ofvariable index, could also be used as microscope ob-jectives for the infrared.7 ' Lastly, stepped-zone mirrorsfor microwaves have been designed which operate bothby reflection and diffraction.7 6 77 Parageometricaloptics has proved to be valuable in the treatment ofthese diffraction reflectors.
Another field which is increasingly related to opticsis that of information theory. Among the studies car-ried out in Italy in this field, some papers by Toraldo diFrancia deserve special consideration because they rep-resent one of the first attempts to formulate anew
May 1962 / Vol. 1, No. 3 / APPLIED OPTICS 281
the central problems of optics according to the methods
of communication theory. Two papers deal with the
statistics of the optical images considered as stochastic
sources7 8 and the capacity of an optical channel in the
presence of noise79 ; but the most important contribu-
tion to this field seems to be the exact formulation of
the theory of resolving power, by means of the sampling
theorem, made by Toraldo di Francia.0The classical concept of resolving power has long
enjoyed the attention of the optical school of Arcetri,
and many objections have been raised, especially by
Ronchi,"1 against the conventional way of defining it.
A crucial argument against conventional resolving
power has been presented by Toraldo, as reported above
(see Section II). The new formulation of the theory
of resolving power is based on the evaluation of the
maximum amount of information which may be con-
tained in an optical image. The degrees of freedom of
an optical image are shown to be a finite number, while
the number of degrees of freedom of the object is infinite.
As a consequence, a large class of different objects may
correspond to a given image, and the actual object can-
not be recognized unless an infinite amount of informa-
tion is available a priori for the observer. In particular,
this holds for the resolution of two points.In the field of practical applications of information
theory reference will be made to a learning machine re-
cently constructed in Italy,8 2 -84 the PAPA (Italian
abbreviation for Automatic Programmer and Analyzer
of Probabilities). This machine has been successfullyapplied to "read" and to recognize patterns.
A contribution to the development of the physics
of radiation is contained in two recent papers where
the method of evanescent waves is applied to the study
of the radiation emitted by charged particles in uni-form straight motion.8586
VI. History of Optics
To conclude this review it seems worth mentioningthat the study of the history of optics has recentlyreceived increasing attention in Italy, mostly as a
consequence of the original work done in this field by
Ronchi. His general history of optics recently ap-
peared in its French edition,87 while a number of papersby the same author deal with particular subjects of
considerable historical interest.88The author wishes to thank Prof. V. Ronchi, Prof.
Toraldo di Francia, Prof. Righini, Ing. Morais, Ing.
Guidarelli, and all the others who have given her use-
ful information about the literature pertaining to thevarious topics treated in this paper.
References
1. 0. Mossotti, Teoria degli strumenti ottici, Pisa (1857).2. L. Billotti, Teoria degli strumenti ottici, Milano (1883).
3. A. Colacevich, Atti fondazione G. Ronchi 1, 139 (1946).
4. A. Colacevich, Atti fondazione G. Ronchi 4, 15, 23
(1949).5. A. Colacevich, Atti fondazione G. Ronchi 2, 43 (1947).
41. M. Bittini, Atti fondazione G. Ronchi 15, 606 (1960).
42. Lucia Ronchi and G. Mori, Atti fondazione G. Ronchi 15,
46 (1960).
282 APPLIED OPTICS / Vol. 1, No. 3 / May 1962
43. F. Mori and Lucia Ronchi, Atti fondazione G. Ronchi 15,138 (1960).
44. M. Conticelli and Lucia Ronchi, Atti fondazione G. Ronchi15, 369 (1960).
45. Lucia Ronchi and G. Mori, Atti fondazione G. Ronchi 14,495 (1959); ibid. 15, 357 (1960).
46. Lucia Ronchi and S. Grazi, Optica Acta 3, 188 (1956).47. Lucia Ronchi and J. D. Moreland, Optica Acta 4, 31 (1957).48. Lucia Ronchi and P. Strocchi, Atti fondazione G. Ronchi
12, 61 (1957).49. Lucia Ronchi, Atti fondazione G. Ronchi 14, 384 (1959).50. M. Bittini and Lucia Ronchi, Atti fondazione G. Ronchi 15,
53 (1960).51. V. Ronchi, Optics, the Science of Vision (New York Univ.
Press, 1957).52. A. Fiorentini, M. Jeanne, and G. Toraldo di Francia, Atti
fondazione G. Ronchi 10, 371 (1955); Optica Acta 1, 192(1955).
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453 (1957); ibid. 13, 145 (1958).55. A. M. Ercoles and A. Fiorentini, Atti fondazione G. Ronchi
13, 155 (1958); ibid. 14, 230 (1959).56. A. Fiorentini and A. M. Ercoles, Optica Acta 4, 150 (1957);
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59. G. Salvi and G. C. Guzzinati, Ann. ottalmol. e clin. oculist.84, 358 (1958).
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(1960).62. U. Volpi and G. Venturi, Atti fondazione G. Ronchi 14, 63
(1960).63. G. C. Guzzinati and G. Bertoncini, Ann. ottalmol. e clin.
oculist. 86, 98 (1960).64. C. Toselli and D. Andreani, Ann. ottalmol. e clin. oculist. 81,
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1681 (1958).68. M. Mancia, M. Meulders, and H. G. Santibanez, Arch. ital.
biol. 97, 378, 399 (1959).69. G. Toraldo di Francia, Optica Acta 1, 157 (1955); Problems
in Contemporary Optics (Florence, 1956), pp. 190, 196.70. N. Carrara, Laura Ronchi, M. Schaffner, and G. Toraldo di
Francia, Alta Frequenza 27, 116 (1957).71. A. M. Scheggi and G. Toraldi di Francia, Alta Frequenza 29,
438 (1960).72. G. Toraldo di Francia, Ann. Mat. 44, 35 (1957).73. G. Toraldo di Francia, J. Opt. Soc. Am. 47, 566 (1957).74. G. Toraldo di Francia and M. T. Zoli, Atti fondazione G.
Ronchi 13, 223 (1958); ibid. 15, 90 (1960).75. G. Toraldo di Francia, J. Appl. Phys. 32, 2051 (1961).76. Laura Ronchi and G. Toraldo di Francia, IRE Trans.
Antennas and Propagation AP-6, 130 (1958).77. G. Toraldo di Francia, Laura Ronchi, and V. Russo, IRE
78. G. Toraldo di Francia and M. T. Zoli, Problems in Contem-porary Optics (Florence, 1956), p. 64.
79. G. Toraldo di Francia, Optica Acta 2, 5 (1955).80. G. Toraldo di Francia, J. Opt. Soc. Am. 45, 497 (1955).81. V. Ronchi, Proc. Symposium Astron. Optics, Manchester,
1955.82. A. Gamba, Proc. IRE 49, 349 (1961).83. A. Gamba, L. Gamberini, G. Palmieri, and R. Sanna, Suppl.
Nuovo cimento 20, 112 (1961).84. A. Gamba, G. Palmieri, and R. Sanna, Suppl. Nuovo ci-
mento 20, 146 (1961).85. G. Toraldo di Francia, Nuovo cimento Ser. 10, 16, 61 (1960).86. Laura Ronchi, V. Russo, G. Toraldo di Francia, and C.
Zaccagnini, Optica Acta 8, 281 (1961).87. V. Ronchi, Histoire de la Lumiere (Colin, Paris, 1957).88. V. Ronchi, Atti fondazione G. Ronchi 3, 155 (1948); ibid.
4, 38 (1949); ibid. 9, 362 (1954); ibid. 10, 154 (1955);11, 189 (1956); I cannocchiale di Galileo e la Scienza delSeicento (Einaudi, Torino, 1958).
ICO MUNICH 1962
US delegates to the Sixth Congress of the International Commission of Optics are W. LewisHyde (leader), R. C. Jones, and D. Z. Robinson, with alternates Mary E. Warga, StanleyS. Ballard, and G. Hass. For more information about the ICO Munich meeting. see page 252.
