Modern motion-picture lenses and their testing

Modern motion-picture lenses and their testing

E. V. Gavrilov

ZAO Optika-Élit, St. Petersburg

V. K. Kirillovski

St. Petersburg State University of Information Technologies, Mechanics, and Optics, St. Petersburg�Submitted December 8, 2004�Opticheski� Zhurnal 72, 47–56 �October 2005�

This paper presents schematic optical diagrams of new lenses for professional cinematography.Methods are considered for monitoring the quality parameters of the images formed by the lensand the errors in fabricating the lens components. © 2005 Optical Society of America.

Progress in the development of detector systems hasbrought about a substantial reduction of the size of cameraswhile simultaneously improving the quality of the recordedimage. As the resolving power of the detector systems in-creases, the requirements on the quality of the image formedby the camera optics have become greater, while the de-crease of the camera size has promoted an increase of theangular field of the lenses that are used.

I. CLASSIFYING THE LENSES OF MOTION-PICTURE ANDTELEVISION CAMERAS

A number of attributes1 can be used to divide the entirediversity of lenses into classes, groups, types, and forms.

In terms of the form of application, there are three largeclasses of camera lenses:

• for standard television �SDTV�,• for high-definition television �HDTV�,• for professional cinematography.

In terms of purpose, seven groups of camera lenses canbe distinguished:

• for studio transmissions,• for outdoor imaging �electronic field production, or EFP�,• for video journalism �electronic news gathering, or ENG�,• for electronic cinematography �Cine Style�,• for film cinematography,• for video conferencing,• for macro imaging.

In terms of basic optical characteristics, lenses can bedivided into five forms:

• long focal length �f��150 mm, neglecting extenders�,• fast �1:F�1:2�,• wide angle �2wmax�70° �,• high zoom ratio �M �50� �,• standard, with medium characteristics �1:F�1:2, 2wmax

�70°, M �50��.

In terms of the size of the recorded image frame, thereare the following lenses:

773 J. Opt. Technol. 72 �10�, October 2005 1070-9762/2005/1

• for motion-picture film: lenses for film formats S16 mm,35 mm, and S35 mm;

• for CCD-array format: 1 in., 2 /3 in., 1 /2 in., and 1/3 in.

We regard lenses for 35-mm film as the most frequentlyused in professional motion-picture cameras.

II. MOTION-PICTURE LENSES FOR S35-mm FILM

Lenses for the S35-mm film format are most frequentlyused in professional motion-picture cameras. The quality ofthe optical image of such lenses must satisfy the followingconditions:

• high image contrast: at least 0.5 at 40 lines/mm, at least0.4 at 60 lines/mm, and at least 200 lines/mm for visualcalibration of the lens over the entire image field;

• maintenance of geometrical similarity of the picture beingphotographed by its image, which requires distortion to becorrected to within no worse than 5%, except for fish-eyecameras;

• compensation of the pumping effect, or pulsing of the im-age; i.e., the variation of the scale of the image at finitedistances must not exceed 3%.

The focal lengths of a linear array that has been devel-oped range from 9.6 to 500 mm. This corresponds to field-of-view angles from 155° to 2.5°.

The objectives most widely used in the linear array arethose whose focal lengths equal 28, 35, 40, 50, 75, and100 mm.

In developing such lenses, most of the attention is paidto design simplicity, manufacturability of the components,and assembly of the lens as a whole.

The required parameters of the lens can be achieved insome cases by choosing a well-known starting layout and byadding components with properties that are already known.In general, when developing new optical systems with aug-mented parameters, it is most efficient to use the method ofcomposition of optical systems proposed and developed byM. M. Rusinov.2

The main technical characteristics and schematic dia-grams of some modern professional lenses are shown inTable I.

77300773-08$15.00 © 2005 Optical Society of America

The group of fast, wide-angle lenses includes anastig-mats with focal lengths 9.6, 12, 14, 16, 18, 20, 22, and24 mm, developed on the basis of original layouts. The cre-ation of such systems is a very complex problem, and thedifficulties encountered when they are being developed in-clude the following:3,4

• the need to provide sufficiently high image illumination atthe edges of the field of view,

• the need to eliminate a number of nonelementary aberra-tions that occur only at large angular fields,

• the need to use geometrical vignetting to eliminate fieldaberrations.

The optical setups of such lenses are an extension of thesetups used when designing the lenses of a basic linear array,supplemented with certain components with known dimen-sional and aberrational properties.

Such lenses have a field of view greater than 70°, and thetask of reducing the diameter of the first lens presents seriousdifficulties for the designer. The first problem is associatedwith correcting aberrations. It is the direct consequence ofsuch a limitation of the size of the first lens, since this sizewas not an essential factor in designs developed earlier, andthe problem was solved quite satisfactorily. The entrance pu-pil is usually located at about the interval of one focal lengthf� from the front element, and the image distance is oftengreater than 2f�. Such a combination is achieved when thefirst component has a significant negative power. Here themain problem is to correct the distortion and astigmatismsimultaneously, especially if one keeps in mind the chro-matic variations of the distortion and astigmatism when thelens is focused at finite distances.

Compensators based on pairs of negative meniscuses areused to completely correct distortion in this kind of lenses.To simplify the process of fabricating wide-angle lenses, a

TABLE I. Schematic diagrams of lenses of a basic linear array.

774 J. Opt. Technol. 72 �10�, October 2005

combination of a weak positive lens in front of a negativelens is used that is capable of introducing positive distortionand thereby of compensating the negative distortion of theentire front component. This approach was used, for ex-ample, when designing a lens with f�=20 mm �see Table II�.

The second problem is associated with focusing. Thevariation of aberrations, especially those that depend on ap-erture, shows up more clearly in lenses whose parameters areat their limit. Our analysis of the schematic diagrams showedthat the following schematic diagrams for lenses that possessthe minimum pumping effect are possible. In this case, tocompensate the variation of the field-of-view angle of thelens in the process of focusing, a special zoom system me-chanically associated with the focusing movement is used init. Because of the necessity of compensating a relativelysmall change of the focal length to compensate the pumpingeffect, the optical layout of such a lens with variable focallength is significantly simplified. The lens can also be basedon an ordinary lens in combination with a multiplexer, lo-cated between the last surface of the lens and the imageplane. The pumping effect is compensated by varying thefocal length of such a multiplexer.

The illumination of the lenses considered here obeys thecos4 � rule even with vignetting caused by aberration in theimage of the entrance pupil, and even when the slope angleof the off-axis rays in image space is reduced.

The main technical characteristics and schematic dia-grams of some short-focus and medium-focus lenses thathave been developed are shown in Table II.

The group of fast long-focus lenses includes anastigmatswith focal lengths 200, 300, and 500 mm, based on the de-sign of the Telegoir and Tair lenses.

By replacing the front component in the f�=300 mmlens with a more complicated three-lens combination, it was

774E. V. Gavrilov and V. K. Kirillovski

possible to achieve high image quality and increase the rela-tive aperture.

The secondary-spectrum problem inherent to long-focallenses is successfully solved by using synthetic fluorite or bya reasonable choice of ordinary kinds of glass, for example, acombination of TF4, TF5, TF10 with OF4, STK19, and oth-ers. A fairly high level of correction of the secondary spec-trum can then be obtained with a comparatively simple lensdesign.

The main technical characteristics and schematic dia-grams of some long-focus lenses are shown in Table III.

III. STAGES IN THE CREATION OF A LENS

The lens parameters indicated in Section II are achievedin the process of creating the lenses by solving two mainproblems:

1. the problem of a modern lens design in which the resultof the calculation, i.e., the mathematical model of thelens, shows that the resulting design parameters provide

TABLE II. Schematic diagrams of wide-angle lenses.

TABLE III. Schematic diagrams of long-focus lenses.


the necessary transfer factor of contrast and distortion, aswell as minimizing the pumping effect and stray illumi-nation caused by light scattering;

2. the problem of fabricating the components of the lens andof the entire optical system in accordance with the calcu-lation, i.e., of ensuring that

�a� the accuracy of the specified calculated sizes is in ac-cordance with the allowances,

�b� the refractive index and dispersion of the optical mediaare in accordance with the results of the calculation,

�c� the inhomogeneity and striations in the glass do notviolate the requirements of the design documentation.

IV. CORRECTION OF MODERN MOTION-PICTURE LENSESAND CONTROL PROBLEMS

The optics of lenses for professional cinematographyhave thus achieved a high level. Modern concepts, methods,and software for calculations of optical systems and progress


in the development and production of optical glasses havemade it possible to create lenses whose calculated character-istics are fairly high. Thus, considering the calculated char-acteristics of the systems mentioned above, we can state thata compound lens �see, for example, Table I� forms a wavefront whose deformation does not exceed �W� �2–3��.Keeping in mind that, on the average, the setup containstwenty optical surfaces, we find that the requirements on thefabrication accuracy of each surface are at the level of �N=0.2 �ring�, which corresponds to �Wsurf�0.1�. Such highrequirements are explained by the fact that the surface errorsin a compound system add up. To monitor such small errors,methods and facilities are needed that possess the appropriatesensitivity, and, to quantitatively estimate the image qualityand aberrations of systems under production conditions,measurement facilities are needed whose errors are substan-tially smaller than the errors of the system being tested.

In fabricating lenses, there are currently a number ofoperations whose quality is determined by the operator’sskill. These subjective factors must be eliminated fromamong the dominant factors by improving the technologiesfor the test facilities and by using modern high-tech appara-tus and test methods.

To solve these problems under actual production condi-tions, methods and processing equipment must be developedthat provide the required fabrication accuracy.

The test methods and devices of modern optics mustprovide the following:

1. testing of the fabrication errors of optical components, therequirements on the accuracy of which with respect toerrors of the optical surfaces are, as shown, �Wsurf

�0.1�;2. measurement of the quality characteristics of the image

formed by the system, and estimation of the image qual-ity;

3. measurement of the aberrations of the fabricated systemfor certifying it with respect to compliance withcalculation.

In formulating the requirements on the characteristics ofthe apparatus for process control of the lenses of modernmotion-picture optics, we should point out the following:Test apparatus is needed that makes it possible to monitor�N without using test glasses; i.e., noncontact methods areneeded, since superimposing a test glass makes it almostimpossible to avoid dynamic and thermal strains of the opti-cal surfaces commensurable with an error of 0.1�. Thus, aninterferometer is required whose inherent error is a factor of5–10 lower than the error to be measured; i.e., it must be�0.01–0.02��.

V. REQUIREMENTS ON THE ACCURACY OF REFERENCEELEMENTS FOR CLASSICAL AND TRADITIONALINTERFEROMETERS

It the test surface of an optical component is brought intocontact with the reference surface of a standard and if theirshapes do not match, an air gap of variable size is formed,which can be regarded as a sheet with thickness h and re-


fractive index n=1 �air, vacuum�. The path difference of thelight rays with wavelength � that are incident on the sheet atan angle of and are reflected by the optical surfaces thatbound the gap is5

= 2h cos +�

2. �1�

When the light is incident along a normal to the surface,we have cos =cos 0=1, and then

= 2h +�

2. �2�

If the path difference is an even multiple of � /2, thelight becomes stronger. The relative intensity distribution inthe interference pattern is determined by

I = cos2 �

�. �3�

We denote the path difference in wave measure as

� =

�. �4�

If one surface is tilted relative to the other at angle �, thespatial frequency of the interference fringes caused by the tilt�fringes of equal thickness� is

=sin �

�. �5�

At small angles, we use sin �=�. Then

=�

�. �6�

The relative intensity distribution in the interference pat-tern when the tilt of the surface is introduced can be writ-ten as

I = cos2 �� y + �� , �7�

where y is the extent on the optical surface along the normalto the edge of the wedge.

Equation �7� describes the formation of the interferencepattern of two tilted flat or spherical wave fronts. The inter-ference fringes are rectilinear and parallel and are separatedby equal gaps, with a cosinusoidal character of the intensitydistribution in the interference pattern �in the direction nor-mal to the interference fringe�. The quantity � indicates thephase shift in the periodic pattern of fringes on a sectionwhere there is an additional path difference caused by errorof the optical test surface if the reference surface has noerrors.

To form the reference wave front in traditional interfer-ometers �for example, those that use the Fizeau or Twyman-Green layout�, it is necessary in their design to use a refer-ence optical element �usually a flat or spherical referenceoptical surface�. Such an element creates a wave front con-taining unavoidable residual errors �deformations�. These er-rors have a number of causes, including


1. residual fabrication errors, because the traditional meth-ods used for processing and testing accurate optical sur-faces do not guarantee that their shape errors will be lessthan � /20;

2. the possibility of uncontrolled shape change of the opticalsurface of the reference component. The presence of sucherrors will promote

�a� dynamic effects �for example, pinching in the mounts�,�b� gravitational effects �breakdown of the unloading of a

component�,�c� temperature effects,�d� vibrational affects.

In practice, the intensity distribution on the interferencepattern is thus determined by

I = cos2 �� y + �T + �R� , �8�

where the phase shift is determined by the sum of errors�R=WR /� and �T=WT /�.

The accuracy of interference monitoring when the otherconditions are definitely obeyed is thus determined by thevalue of WR. Taking into account the usual metrological re-quirement that the error of the measurement method must bean order of magnitude less than the error to be measured onan item, we can determine the typical requirements on themeasurement accuracy of aberrations and the errors of opti-cal systems of different accuracy classes.5 WT is the limitingallowable error of the reference wave front of a device formonitoring the reference surface of an interferometer. It canbe assumed that the values of the required accuracy in thecase of interferometry refer, when the other conditions aresatisfied �vacuum, elimination of the influence of vibrations,etc.�, to the allowable residual errors of the reference wavefront, which in turn are determined by the errors of the ref-erence optical surface.

It is thus possible to formulate requirements on themonitoring of the reference elements of the greatest accuracyfor universal interferometers �of traditional types�:

1. Requirements on the accuracy of a device for monitoringstandards are shown in Table IV.

2. Because the standard may be unstable, it cannot be as-sumed that it is sufficient to calibrate it periodically. Ac-tually, to ensure and maintain the indicated accuracy, itbecomes necessary in practice to carry out effective self-monitoring of the real state of the reference wave frontduring each monitoring session.

TABLE IV. Requirements on the accuracy with whic

Type of optical system

Requirthe accu

system, n

Modern photographic lensOptical surfaces of the objective lenses 0


The studies of Ref. 7 showed that these conditions canbe satisfied by creating an alternative interferometer in whichthe reference wave front is stopped down.

VI. CHOOSING A SYSTEM SOLUTION FOR ANINTERFEROMETER

One of the most widely used methods of studying wave-front deformations, including those associated with shape er-rors of high-precision polished surfaces and aberrations ofthe focusing optical systems, is the interferometry method.

System solutions of traditional interferometers are basedon the formation of a reference wave front by using referenceoptical surfaces. Such devices include standard classicalTwyman and Fizeau interferometers10,11 �for example, Fig.1�.

The well-known advantages of such system solutionsserved as a basis for using them extensively. However, therehas been increased demand in recent decades for optical sys-tems and elements of a high accuracy class. Today suchitems include the optical systems of professional motion-picture lenses. The requirements on the accuracy of theiroptical surfaces, as has been shown, are at the level of�0.1–0.2��. Thus, for monitoring when they are being fabri-cated and used, devices are needed that provide accuracy at alevel of �0.01–0.02��, i.e., an order of magnitude more ac-curate than the traditional value.

A disadvantage of classical interferometers in monitor-ing the optics of the highest accuracy class is the need for

optical devices are monitored.

ts onof these than

Requirements onthe accuracy of themonitoring device WR WT

�0.1–0.2�� 0.15� 0.015�

�0.01–0.02�� 0.015� 0.003�

FIG. 1. Twyman interferometer. 1—laser, 2 and 3—lens elements of theilluminator system, 4—stop, 5—collimator lens, 6—beamsplitter, 7—opticalsystem being investigated, 8—reference spherical surface, 9—reference flatsurface, 10—observation-system lens, 12—image detector �for example, theeye�.

h the

emenracyo wor

1�

.1�


them to include a reference optical element, whose fabrica-tion accuracy is limited. In this case, there is no guaranteeagainst an uncontrolled change of the accuracy of the refer-ence optical element during operation of the interferometer.

An alternative approach to interferometry is to createinterferometers in which a spherical reference wave front iscreated by diffracting a radiation beam focused at a pinhole8

whose diameter is commensurate with the wavelength. Thefirst known layout of this type was proposed by Linnik9 �Fig.2�.

Here a diffracting aperture in a semitransparent opticalcoating is set in the plane of the circle of confusion formedby the optical system being tested in the monitoring layout.The disadvantages of such an interferometer with coincidentarms are that it has a difficult adjustment process that differsfrom the traditional, low quality of the interference patternand definite complexities in its interpretation.

A laser interferometer with a diffracted reference wavefront and separate arms showed high efficiency in the moni-toring of high-accuracy optical surfaces and systems6,10 �Fig.3�.

Numerous interferometer layouts have been developedwith a stopped-down reference wave front. These devicesuse the traditional technique for adjusting and interpretingthe interference pattern and provide high interferogram qual-

FIG. 2. Layout of Linnik interferometer. 1—lamp, 2—condenser, 3—filter,4—pinhole, 5—collimator lens, 6—optical system being investigated,7—exit pupil, 8—wave front formed by test system, 9—Linnik plate, 10—beamsplitter coating with pinhole, 11—distorted wave front being investi-gated, 12—diffracted spherical reference wave front, 13—interferencepattern.

FIG. 3. Interferometer with diffracted reference wave front and autocolli-mation illuminator arm. 1—laser, 2 and 3—illuminator system, 4—tiltedmirror, 5—pinhole, 6 and 7—counter collimation lenses, 8—flat autocolli-mation mirror, 9–11—elements of observational microscope with Bertrandlens, 12—video camera, 13—video-signal processing unit, 14—unit for dis-tinguishing the centers of the interference fringes, 15—television monitor,16—computer, 17—surface to be measured.


ity, flexibility when studying optical systems and elementswith various transmittances �reflectances� from 98% �specu-lar coatings� to 0.15% �antireflection coatings�.

The device is distinguished by the absence of referenceoptical elements and the errors produced when they are beingfabricated; it is simple in design, compact, and easy to oper-ate.

On the other hand, an analysis7 of the transformationfunction �TF� for the method of interferometry of wave-front

deformations shows that the relative intensity I in the inter-ference pattern is associated with wave-front distortions ��in wave measure� by the periodic dependence

I = cos2 �� . �9�

Here I= Ii / I0, where Ii is the intensity at a given point of theinterference image, I0 is the intensity at the same point in theabsence of aberration, �=W /�, where W is the normal de-viation of the wave front, and � is the wavelength of theradiation in the interferometer. An analysis shows that anumber of advantages are created here by the periodic char-acteristic of the sensitivity:

1. obvious display of the pattern of wavelength errors,where the interference fringes play the role of isolines;

2. the quantitative character of the method, where the inter-ferogram is convenient for direct geometrical measure-ments of the coordinates of the position of the fringesassociated with the wave-front errors being studied.

Reference 7 gave an analysis of the possibilities andlimitations of methods and facilities for studying high-precision surfaces. The disadvantages of smooth transforma-tion characteristics include

• limited dynamic range lying within the framework of thelinear section of the TF,

• low sensitivity of visual measurement positioning, associ-ated with the indistinctness of the image elements �darkpattern, circle of confusion, hartmannogram spots�;

• high redundancy of the information accompanying auto-matic deciphering and interpretation of such images.

To eliminate the above drawbacks and to obtain efficientmethods and facilities for studying high-precision surfacesthat possess new properties and expanded possibilities, a sys-tem of one-dimensional TFs is developed.7 A number of typi-cal TFs are presented, to which are assigned conditionalnames in quotation marks matching the external shape of thegraph of the function: “pulse” and “comb.”

Since the invariant dependences discussed here can beassociate different quantities in different specific cases,single values of the function and the argument are taken forall the TFs: Wy,z is the independent variable corresponding tothe two-dimensional parameter being studied, and Iy�,z� is thedependent variable corresponding to the two-dimensional in-tensity distribution in the optical-measurement image.

The TF method of studying pulse-type precision surfacescan be explicitly represented by an expression using the


function: I=�W�=lim N exp�−N2�W2�, which takes theform I�W�= Imax when W=0 and I�W�=0 when W�0.

The periodic TF method of studying comb-type preci-sion surfaces can be explicitly represented by

Iy,z = comb�W/�W� = �n=1

N

�W − n�W� ,

where �W�W�n�W. In practice, it can be determined as

I�W� = Imax whenW

�W= 0,1,2,3 . . . ,

I�W� = 0 whenW

�W� 0,1,2,3 . . . .

Analysis showed that the TF system that has been devel-oped gives a number of special positive effects, such as con-servation of information redundancy, improvement of theclarity and detection of new details and properties of theobject, increase of the sensitivity of the monitoring and mea-surement accuracy, increase of efficiency and productivity,and simplification of the task of automating the monitoringand investigations.

The apparatus developed for these invariant transforma-tion functions, as shown by studies, becomes the theoreticalbasis for modern methods of processing optical measurementdata and creating modern computerized methods of opticalmeasurements and testing, including new principles, algo-rithms, and software.

The mutual influence of the methods synthesized forstudying high-precision surfaces with these new results andmethods is also illustrated using the example of the proposed�and implemented in the form of a commercial device�method of isometry of the second derivative of the spatialintensity distribution function, making it possible, for ex-ample, to distinguish the centers �axes� of the interferencefringes. This development allowed an automatic interferom-eter of a new type to be created, making it possible to in-crease the accuracy with which interferograms are inter-preted by a factor of 10–40 in real time.

The operation of electronically distinguishing and visu-alizing the centers of interference fringes �Fig. 4� with mul-tiplication of the frequency of the fringes is accomplishedaccording to a TF of the form

Icon = comb� 1

��y sin � + kW�� ,

where Icon is the relative intensity in a contoured interfero-gram, � is the tilt angle of the reference wave front of the

FIG. 4. Interferogram-processing stages.


interferometer relative to the working wave front, W is thewave aberration, y is the coordinate in the interferogram,oriented along the normal to the direction of the interferencefringe, and k is the fringe-magnification factor.

If k=2, the step value of an interference fringe is � /4,and this creates the effect of interferometry using radiationhaving ��300 nm.

The accuracy with which the coordinates of the interfer-ence fringes are determined increases, as shown by studies,by a factor of 40 by comparison with the measurement ac-curacy of an unprocessed interferogram, and this correspondsto the possibility of visually detecting wave-front deforma-tion at a level of � /200 in real time.

The accuracy characteristics of the device for studyingprecision surfaces depend on the principle and design of themeasurement converter and can be determined from ananalysis of the transformation function.

The generation of an undistorted spherical referencewave front in the given diffraction interferometers is thusbased on the use of the easily reproduced physical phenom-enon of diffraction of a laser beam at a pinhole with a diam-eter commensurable with the wavelength. These devices con-tain no reference optical component and are free from theinherent unavoidable residual errors that arise during its fab-rication.

The test and certification of the implemented devicescaused no errors exceeding 0.02�. Practice in operating dif-fraction interferometers with a television analog interfero-gram analyzer �TAI-1� showed that wave-front errors at the0.005� level could be detected and estimated in real time inthe interactive regime.

Spherical concave surfaces can be monitored with such adevice to within an accuracy better than 0.01 wavelength.

The advantages of certifying devices using interferom-eters with diffraction by a pinhole are

• the absence of fabrication errors of the standard,• simplicity of design,• simplicity of adjustment,• reduced vibration sensitivity,• reduced size,• high quality of the interferogram.

The methods and automated apparatus thus developedcan be used in various areas of science and practice for ex-panding the possibilities of optophysical studies, test, andmeasurement.

VII. DEVELOPMENT OF METHODS AND TECHNIQUES OFDIFFRACTION INTERFEROMETRY IN THE AREA OFTHE MONITORING OF SYSTEMS AND ELEMENTS OFMODERN MOTION-PICTURE LENS OBJECTIVES

The basic layout of the diffraction interferometer makesit possible to monitor a concave optical spherical surfacewith the highest accuracy in the referenceless regime, i.e.,directly by means of a diffraction wave front.

A significant number of convex surfaces in objectivesrequire other system solutions. In practice, one of the mostwidely used interferometers for these purposes is the Fizeau


interferometer �Fig. 5�. As is well known, the Fizeau layoutimplements the principle of noncontact test glass.

The use of high-coherence laser radiation makes it pos-sible, by using one reference surface, to monitor convex testsurfaces with radii of curvature within the limits of the radiusof curvature of the reference surface, as well as with anaperture that lies within the limits of the aperture of the ref-erence surface.

Note that, in this case, for concave test surfaces, theradius of curvature is limited only by the coherence length ofthe radiation. For example, for He–Ne lasers, this is tens ofmeters.

The use of the principles of diffraction interferometrywhen working with a Fizeau interferometer can noted in thefollowing directions:

• constant monitoring with a diffraction interferometer of thestate of the reference surface during the operating sessionof a Fizeau interferometer,

• formation of the diffraction wave front by a pinhole, whichavoids the influence of aberrations created by the illumina-tor system of the interferometer.

The fabrication of the components and systems of aFizeau interferometer in a setup using a diffraction interfer-ometer creates the possibility of developing and fabricating aFizeau interferometer of a completely new type.

For example, the allowance on the wave front aberra-tions of Zygo interferometers �analogs of the IKD-U andIKD-110� is �W=1.6� when the accuracy of the referencesurface is �0.1–0.2��.

It is understood that, when the requirements on the ref-erence surface are toughened to the 0.01� level, the allow-ance on �W is 0.16�. Thus, the setup for monitoring theinterferometer must be calculated and fabricated in another

FIG. 5. Fizeau interferometer. 1—laser, 2 and 3—elements of the illumina-tor system, 4—pinhole, 5—beamsplitter, 6—collimator lens, 7—lens of in-terferometer with reference front surface, 8—component with convexspherical surface being used, 9—observer stop, 10—projection lens of ob-servation system, 11—image detector, 12—computer.


way, which cannot be done without using diffraction inter-ferometry.

An analysis of the possibilities of systems developed fordiffraction interferometry shows that interferometry facilitiesof this class make it possible

• to monitor the errors of optical surfaces without using testglasses, in the contactless regime;

• to fabricate and monitor reference surfaces for traditionalinterferometers, reaching an error at the 0.01� level;

• to monitor optical surfaces with any reflectances �specular,antireflection, uncoated� without replacing the reference el-ement �the standard� in the interferometer;

• to implement an interferometer that provides self-monitoring of the reference surface during each operatingsession, that determines the pattern of residual shape de-viations of the reference surface at the time of monitoring,and that introduces these data into a computer to efficientlycorrect the results of the measurement.

VIII. CONCLUSIONS

Lens diagrams have been presented that provide highimage contrast over the entire aperture, small values of thetransverse and longitudinal spherical aberrations, minimumdistortion, and constancy of the image quality during focus-ing at finite distances. The requirements on the monitoring ofmodern cinematographic optics have been considered. Wayshave been shown to enhance the monitoring accuracy for thebest approximation of the calculated models to a producibleproduct.

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Documents

Modern motion-picture lenses and their testing