US2986071A

US2986071A - Photographic objectives

Info

Publication number: US2986071A
Application number: US564704A
Authority: US
Inventors: James G Baker
Original assignee: Perkin Elmer Corp
Current assignee: Applied Biosystems Inc
Priority date: 1956-02-10
Filing date: 1956-02-10
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30
Also published as: DE1154288B; CH357212A

Description

y 1961 J. G. BAKER 2,986,071

morocmpmc OBJECTIVES Filed Feb. 10, 1956 :s Sheets-Sheet 2 STOP 15 R 1 2 L l2 2 Lens R0d'11 Thicknesses n v Gloss Types I R 0.631 1, 0.079 1.70065 47.9 701479 [1' R -I.I26 f 0.007 1.64900 33.9 649339 V R -o.366 '1 0.015 I.5l868 64.2 519642 R" -O.43| S 0.002

The stop lies 0.101 from the vertex of R toward the vertex of R S =ihe buck focal distance.

D= Length of IO waves of sodium light.

2 l3 R; D D

'3 12 [1111 TOR.

Mil BY y 1961 J. G. BAKER 2,986,071

PHOTOGRAPHIC OBJECTIVES Filed Feb. 10, 1956 3 Sheets-Shoot 3 Lens Radii Thicknesses n v Glass Types 1X I R 0.535 t, 0.075 |.755t0 47.2 755472 R l.667 t 0.007 1.68900 30.9 689309 R L06! 5, 0.002

[U R 0.3|2 t 0.050 |.755IO 47.2 755472 I] R 0.8l7 t 0.0l3 LSOSOO 37.9 605379 Y R -0.39s 0.013 |.6203l 50.3 520503 R |.e09 S 0.020

II. R o.s0s t 0.054 1.50370 4|.a 8044i 0 111 R, 5.00| t 0.007 |.72000 29.3 720293 E11 R 0.435 t 0.075 1.74450 45.5 745455 K R piano t 0.020 |.5I700 64.5 5|7s45 R piano 3 0.050

The stop lies 0.||47 from the vertex of R toward the vertex of R =the back focal distance.

The surface R ls aspheric and is of such 0 shape that at 0.32 radians off-axis, the thickness reaches a maximum; at 0.42 radians off-axis, the thickness is approximately equal to the thickness at the optical axis. The maximum variation in thickness is approximately 0.0!! of the focal length.

VENI'OR.

FIG. 3. a... i 5%. 84m gal/36; 6M4:

United States Patent PHOTOGRAPHIC OBJECTIVES James G. Baker, West Somerville, Mass, assignor to The Perkin-Elmer Corporation, Norwalk, Conn., a corporation of New York Filed Feb. 10, 1956, Ser. No. 564,704

Claims. (CI. 88-57) This invention relates to photographic objectives of the Gauss type, which comprise a pair of meniscus components of net divergent effect lying between collective components and concave to each other on opposite sides of a central stop. More particularly, the invention is concerned with a novel objective of the kind stated, which is characterized by unusual excellence in its correction both for the lower order aberrations and for oblique spherical aberration and higher order astigmatism. The new objective is especially adapted to meet the requirements of modern night aerial photography for an objective of medium focal length, speed, and coverage as typified by a 12" f/2.5 lens covering a 55 degree total field, and examples of the objective in that form will, accordingly, be illustrated and described in detail for purposes of explanation.

It has long been known that Gauss objectives are capable of providing a large well-corrected field for both visual and photographic purposes and that various modifications of such objectives permit correction according to the uses to which the objectives are to be put. However, these objectives have deficiencies limiting their speed and coverage and a notable example of such a deficiency is the appearance of spherical aberration at considerable off-axis angles, which is referred to as oblique spherical aberration and is merely the reappearance of the on-axis spherical aberration amenable to control. Oblique spherical aberration generally varies as the square of the field angle off-axis and as the cube of the relative aperture, so that, in a Gauss lens, which covers a large angular field at high speed, serious difficulties arising from oblique spherical aberration can be anticipated and such difficulties are intensified, if the focal lengths required are appreciably greater than those generally used for ordinary photography.

Another deficiency in Gauss objectives is the tendency of the higher order astigmatism to deteriorate rapidly with an increase in field angle. This tendency is so pronounced that unusual corrective means for control of the aberration must be utilized in lenses for the purposes for which the new objectives are employed.

In my Patent 2,532,751, issued December 5, 1950, I have shown how an increase in the central air space of a Gauss objective can be employed to reduce oblique spherical aberration by eliminating most of that part of the aberration varying as the cube of the aperture and limiting its contributions to residuals varying as the fifth and higher orders of the aperture. Also, in Patent 2,671,380, issued March 9, 1954, I have shown how compensating "ice means may be introduced into the central air space of such an objective to achieve advantages including the correction of oblique spherical aberration. Thus, by use of the expedients disclosed in the patents, oblique spherical aberration can be reduced in amplitude and its contribution for any given zone and field angle may be brought approximately to zero.

In work on the development of a Gauss objective in the form of a 12" f/2.5 night lens covering a 55 degree field, I have found that such a lens constructed in accordance with the teachings of the patents falls short of optimum performance. In fact, it appears that the use of the relatively strongly-curved surfaces around the central stop, which are required in such objectives having a large central air space, leads to an actual increase in the oblique spherical aberration in the skew direction. The normal oblique spherical aberration of such an objective having flattened curves around the central stop causes a considerable extension in the tangential direction in the image of a point-source for only a moderate extension in the skew direction, while such objectives having a large central air space and the required steeper curves have less oblique spherical aberration in the tangential direction and more in the skew. In the latter objectives, the rate of change in the aberration over the field is comparatively small, so that the objectives yield off-axis images of excellent quality. However, if a still further improvement in off-axis image quality is to be obtained, the oblique spherical aberration in the skew direction must be further reduced, while the correction of that aberration in the tangential direction is maintained.

The present invention is directed to the provision of a novel objective of the Gauss type, which is superior in performance to the objectives of the patents and in which a number of expedients have been employed in a new combination to achieve the desired result. The objective comprises a pair of outer components of net collective effect, which may be simple elements or compound components, and a pair of inner meniscus components of net dispersive effect lying concave to each other and each composed of two or more elements. The surfaces around the central stop are of relatively weak curvature and materials of medium to high index of refraction are employed for the positive elements of both components with the result that the lens speed is maintained despite the shallow curves. in addition, the dioptric powers of the respective outer collective components and of the concave surfaces adjacent the central stop are all kept within specified limits and, when the outer collective components are cemented, the index differences across the cemented surfaces are restricted. Various other expedients employed in the new objective to insure its extraordinarily excellent performance will be pointed out in the detailed description to follow.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which Figs. 1 and 2 are diagrammatic views of two different lenses embodying the invention with tables of data for the lenses;

Figs. 1A and 2A are fragmentary views on an enlarged scale showing the use of aspheric curvature on two of the1 surfaces of the lenses of Figs. 1 and 2, respectively; an

Fig. 3 is a diagrammatic view of a modification of the lens of Fig. l, with which a field flattener is used, and a table of data for the modified system.

The form of the new objective illustrated in Fig. 1 has been found to be optimum for a 12" f/2.5 night lcns covering a 55 degree field and it is of the Gauss construction. The lens includes outer collective components in the form of cemented doublets, of which the one in front or on the long conjugate side is made up of an outer collective element I and an inner dispersive element 11, while the doublet at the rear or on the short conjugate side is made up of an inner dispersive element VII and an outer collective element Vlll. The collective components surround negative meniscus components, which are concave toward each other around the central stop and are each made of a pair of separated meniscus elements instead of cemented doublets, as is common in prior Gauss lenses. The front meniscus component consists of an outer positive element III and an inner dispersive element IV, while the rear meniscus component consists of an inner dispersive element V and an outer collective element VI. In the lenses illustrated, the corrective action for oblique spherical aberration has been obtained by the use of cemented doublets as the outer collective components, although simple elements with aspheric surfaces could also be employed for the purpose. The positive elements I, III, VI, and VIII of the lens are made of rare earth glasses, although the principles of the invention may be employed in lenses, in which materials of lower index of refraction are used for the positive elements. The improvement gained by the use of the rare earth glasses lies primarily in the added perfection of correction for a given speed, focal length, and coverage.

The lens system of Fig. 2 is closely similar to that of Fig. l with respect to the nature of the components and the elements thereof, but differs from the Fig. 1 system in that the glasses employed are of medium to high index and rare earth glasses are not employed. The corrections of the Fig. 2 lens are different from those of the lens of Fig. l and are not markedly inferior. However. in modern photographic objectives, in which a goal of absolute perfection is sought, a gain of even 20% in performance achieved by the use of the rare earth glasses of the Fig. 1 construction may justify use of such materials.

The invention is based on the use of materials of medium to high index for the collective components and the objectives of Figs. 1 and 2 are typical emodiments of the invention, in which the materials for those components lie within the upper part of the practical index range. If a partial sacrifice of lens speed is permissible. objectives embodying the invention and utilizing the older types of optical glass of medium to low index may be constructed to give a performance otherwise comparable to those of the lenses of Figs. 1 and 2.

In Gauss objectives, the tangential pencils as a rule suffer greater aberrations and a wider range of aberrations over the field that the skew pencils, since the angles of refraction reach maximum value in the meridional plane at practically every surface. Also. the more any given radius of curvature departs from being concentric around the image of the stop in its own medium, the wider the difference between the tangential and skew refractions, which difference is dependent upon the magnitude of the angles of incidence and refraction of the chief rays of the pencils. On the other hand, the corrections for the tangential rays are more responsive than the skew corrections to compensating refractions. Accordingly, I have found it possible by employing a number of elements with comparatively shallow curves with compensating refractions properly arranged in curvature. location, and index difference to effect the necessary corrections for the oblique spherical aberration of the tan- Ill gential rays. The use of such shallow curves then provides the minimum oblique spherical aberration in the skew direction. Additional corrections of considerable value might be obtained by the used of aspheric surfaces, but, in lenses to be manufactured in quantity, such extensive departures from spherical surfaces are not presently feasible.

The objectives of Figs. 1 and 2 have relatively shallow curves compared to prior objectives, and, while shallower curves than those used in the two objectives could be adopted, the use of such shallower curves might result in a system of excessive overall length. Materials of high index ordinarily have a greater absorption of light than low index glasses and, if such high index materials are to be used, economy of light requires that the bulk of the optical system be minimized. The systems of Figs. 1 and 2 are, accordingly, relatively compact for the purpose of keeping the total length of the path through glass to a minimum in compromise with the state of correction. Another advantage of a compact optical system is that it generally involves less vignetting at great offaxis angles, since the various bundles of light generally lie within small solid angles with relation to the entrance pupil. A compact lens is moreover preferable for general use.

In constructing objectives in accordance with the invention, a number of variations within ranges as follows may be adopted. In lenses, such as those of Figs. 1 and 2, in which the outer collective components are cemented doublets, the index differences across the first and last cemented surfaces may vary considerably. In the first component consisting of the elements I, II, element I should have the higher index and the index dilference across the cemented surface defined by the radius R; should be fairly substantial and lie within the range between 0.03 and 0.08. An index difference less than 0.03 may cause excessive curvature of the surface with resultant excessive thickness of the component or overcorrection by the surface, whereas too great an index difference causes both distortion and astigmatism to appear. In the case of the outer collective component at the rear of the system, the converging pencils of light require a greater curvature of the cemented surface in order to obtain the desired corrective action and, because of the greater curvature for high inclination, less index difference is desirable. In the rear collective component, the element VII should have the lower index and the preferred range for the index difference across the surface defined by the radius R has been found to lie between 0.01 and 0.06. It should be noted that, in outer collective components more elaborate than cemented doublets, the index differences mentioned apply to the cemented surfaces curved away from the stop, since the curvatures of other surfaces curved around the central stop are insensitive and of no great corrective action for the purposes of this invention.

As indicated above, the average index for the outer collective components should be as high as practicable, although excellent objectives embodying the invention can be Obtained provided the average index is at least 1.58. As materials having an index in excess of 1.80 are at present notably yellow and, therefore, undesirable, a range of 1.58 to 1.80 may be assigned for the average index of both the front and rear collective components. The term average index as here used is intended to refer to the arithmetical mean of the indices of all the elements of a component, so that, if the component is compound and with or without aspheric surfaces, its average index is the arithmetical mean of the indices of the elements. If the component is a single element, the index of the element is regarded as its average index. while. if the component is a cemented triplet, for example. the average index is the arithmetical mean of the three indices,

The use in the new objective of strong doublets for the outer collective components permits easy color correction and thus imposes less restriction on the choice of materials for the negative meniscus elements adjacent to the central stop. Such negative meniscus elements can, accordingly, have a lower index than is usual in Gauss objectives with a resultant advantage to the Petzval sum. The use of lower index materials for the negative meniscus elements would ordinarily require increased curvatures of the air surfaces adjacent to the central stop and this in turn would have a detrimental effect on the oblique spherical aberration and the on-axis spherical zone. However, in the objectives of the invention, there is a broken contact between the elements of the negative meniscus components and this permits retention of moderate curvatures on the surfaces adjacent the central stop. I have found that the front negative meniscus component should have at least one negative element with an index, which is less than the average index of the front collective component by 0.02 to 0.15. Similarly, the rear negative meniscus component should have at least one negative element with an index, which is less than the average index of the rear collective component by 0.05 to 0.20.

Another feature of objectives of the invention is that the indices of the positive elements of the negative meniscus components can be high without introducing excessive astigmatism, since the elements are of meniscus form. For best results, the highest index of any of the positive elements within the negative meniscus components should be greater than the average index of either the front or the rear collective component and the highest index of the positive elements within either negative meniscus component should exceed the lowest index of the negative elements within that component by from 0.03 to 0.25. This favorable distribution of indices must be kept within bounds in order to avoid an unbalance within the system and an upper limit of 1.85 may be placed upon the indices of the positive elements of the negative meniscus components. In this connection, it may be noted that element VI of the lens of Fig. l is made of a glass of index 1.8.

The limitation of certain constructional features other than the indices of the materials is necessary to define the objectives of the invention and one such feature, which must be confined within definite limits, is the effective lens power ascribed to the collective components where the lens thickness is ignored. In the new objectives, the range of power of the thin-lens equivalent of the front collective component is from 0.45 to 0.75 in terms of the power of the entire system taken as unity. Similarly, the range of power for the rear collective component is 0.75 to 1.10 on the same basis, the range being determined primarily by requirements for correction of distortion and coma,

Another useful limitation defining the structure of the collective components is based on the general degree of bending of the individual components. In the front collective component, a definite meniscus tendency is required and such tendency can best be insured by limiting the dioptric power of the innermost air glass refracting surface, that is, the surface defined by the radius R to the range from 0.2 to 0.8, the power being defined in terms of the power of the entire system taken as unity. The rear collective component can be only weakly meniscus and more generally is weakly biconvex. These characteristics of the component may be defined by specifying that the limit of power of the inner air glass surface lies in the range from 0.3 to +0.4 of the power of the entire system taken as unit. In referring to the power of an individual lens surface, I intend that the term is to be considered in its usual dioptric sense.

When the lens powers and bendings for the collective components have been restricted, as above set forth, the limitations on the form of the negative meniscus components involve chiefly bending. With the Petzval sum reasonably well corrected as in high quality objectives,

the powers of the negative meniscus components are essentially defined, so that consideration of the bendings only remains. Such bendings can best be described by reference to the dioptric powers of the concave surfaces around the central stop and, because of the convergence of bundles of pencils from the long conjugate side, the negative power of the front concave surface is appreciably greater than the power of the rear surface. I have found that, for a favorable flatness of field and correction of spherical aberration, the lens power of the front concave surface adjacent the central stop, that is, the surface defined by the radius R should lie within the range from l.7 to -2.8. The preferred lens power for the rear concave surface adjacent to the central stop, that is, the surface defined by radius R lies between -l.0 and 1.90. In addition, a favorable correction for coma can be readily obtained, when the absolute power of the front concave surface in objectives of the invention is greater than that of the rear concave surface.

A further feature of objectives of the invention, which must be kept within specified limits, is the length of the central air space containing the stop. I have found that, for favorable correction of the oblique spherical aberration in the skew direction, an air space within the range of 0.14 F to 0.28 F is to be preferred, F being the focal length of the system. If a shorter air space is employed, the tangential oblique spherical aberration tends to become uncontrolled, while, if the air space is greater than the top limit stated, a considerable loss of overall lens power results and this demands a general steepening of the curves with consequent aberrations.

In my work in the development of the objectives of the invention, I have observed that quite often the upper and lower rim ray corrections can be materially improved by judicious use of aspheric corrections on the appropriate surfaces. In general, when the lens barrel has an overall length which is a substantial fraction of the focal length of the system, the inclined bundles of rays passing through the entrance pupil strike the front and rear collective components quite far from the optical axis. The extreme rays use the outermost portions of such surfaces in areas not used at all by the bundles toward the central part of the field. Accordingly, it is possible to make use of aspheric corrections in the peripheral zones of such surfaces to influence image formation far off axis without affecting the performance in the central portions of the field. Frequently, it is adequate to select only one such surface in the front portion and another such surface in the rear portion of the lens system. The use of aspheric corrections may be regarded as the addition of a very weak lens element superimposed on a selected lens surface and such an element may be of either positive or negative effect on the particular ray, as required in common with the other design properties of the system. The effectiveness of the aspheric correction utilized in this manner arises from its nearly complete independence of the other parameters already heavily burdened in controlling overall performance. If an objective of the invention is properly designed, the aspheric corrections mentioned can be kept in reserve to be used with the other factors set forth for the purpose of obtaining excellent off-axis images in the extreme corners of the format. In practice, it is far more desirable to employ turned-down edges than turned-up edges, since the former are more easily made, but edges of either sort may be required.

In systems of the invention, the depth of the aspheric corrections at the extreme margin of the clear aperture varies with the specific system and may be only part of the length of a wave of sodium light at wavelength 5893 angstroms. In a 12" f/2.5 lens covering a 55 degree field, the aspheric corrections should have a depth equal to the length of at least five such waves. By depth," I mean the distance at the margin of the aperture in a direction parallel to the optical axis between the basic spherical surface and the superimposed aspheric surface. While a definite upper limit to the aspheric variation cannot be precisely stated, it would be unusual if aspheric corections amounting in axial depth at the margin of the clear aperture to a length of more than 200 waves of sodium light were necessary to achieve a final off-axis correction and, if the maximum axial depth or sagitta of the aspheric correction relative to the basic sphere were greater than the length of 200 waves of sodium light, it is unlikely that the performance of the objective in the intermediate field would be satisfactory.

In Fig. I, the dotted lines L on the element II indicate a turned-down edge (greatly exaggerated) on the surface defined by the radius R which makes that surface aspheric. The dotted lines L; on element VII similarly indicate a turned-down edged (greatly exaggerated) on the surface defined by radius R The turning down of the edges provides aspheric corrections at the margins of the clear aperture and, in the lens of Fig. 1, such corrections have an axial depth D equal to the length of approximately ten waves of sodium light. In the lens of Fig. 2, the dotted lines L and L indicate turned-down edges on the surfaces defined by the radii R and R12. respectively, and the turning down of the edges provide aspheric corrections having an axial depth D equal to the length of approximately ten waves of sodium light.

The constructional data of the objective of Fig. l are substantially as listed in the following tabulations wherein:

Roman numerals indicate elements of lens assemblies;

The symbol R indicates the radius of curvature for the optical surfaces;

1 indicates the axial thickness of optical elements;

S indicates axial separations between adjacent elements;

71 indicates the index of refraction of the glass at the sodium line;

v indicates the reciprocal dispersion of the optical elements; and

The Glass Types" are conventional international code numbers, the first three numerals indicating the index of refraction (less 1) and the next three numerals indicating the reciprocal dispersion (without the decimal point).

The stop lies 0.1147 from the vertex of R toward the Vertex of R S =the back focal distance.

The constructional data of the objective of Figs. 2 are substantially as follows:

Example II Lens Radii Thlckn, 17 Glass nesses Types s.=0.002 R: 0.331 m t; =0.053 1.70065 47.8 701470 S1==0.029 R0 0.960 W 1. =0.015 1.04000 33.0 040338 s,=o. 171 R, =-0.30s 1, =0.015 1.51003 04.2 519642 s,=0.017 Rw=-0.727 v1 t. =0.0s1 1.70005 47.0 701470 s.=0.002 Rn: 2.170 v11 t =0.00s 1.68900 30.0 080309 R"=1.0ss

The stop hes 0.101 from the Vertex of R toward the Vertex of R S =the back focal distance.

After all the various improvements above described have been combined with satisfactory forms of correction for the standard aberrations, there remains a zonal term in the field curvature that is irreducible by any means within the objective so far determined. In the absence of astigmatism, the zonal departure from a flat focal plane for a full field of one full radian amounts in amplitude to about 0.0036 of the focal length and reaches this maximum value at about 0.70 of the distance from the axis to the edge of the specified field. Where necessary, the zonal field curvature referred to can be eliminated by the use of a field flattening lens.

It is well known that an auxiliary field flattener can be placed near the focal plane of an objective to aid in eliminating the zonal field curvature without at the same time affecting the optical corrections significantly, particularly if the latter are balanced with the field flattener in place. Such a field flattening lens can also be used to reduce the Petzval sum of the third order of approximation and this then requires that some weak negative dioptric power be given to the lens. An aspheric deformation can be added to the field flattener to complete the task of flattening the field.

The lens illustrated in Fig. 3 is that shown in Fig. l employed with an auxiliary field-flattener for the purpose of eliminating the residual zonal field curvature. The example of Fig. 3 is typical, but, without departing from the spirit of the invention, the distance of the field flattening lens from the focal surface can be varied or the spherical and aspheric portions of the lens surface can be distributed wholly or in part between the front and the back of the lens. Also, it is possible to utilize a compound lens with spherical or aspheric surfaces in such a' position near the focal plane as to achieve improved correction for field-flatness and elimination of chromatic distortion and residual lateral color.

In general, the field flattener must be quite close to the focal plane in order that the field flattening action may not affect other aberrations irreparably. Occasionally, it may be desirable to have the last surface of the field flattener adjacent the focal plane actually in contact with the plane and, when the back side of the field flattener is flat and coincident with the focal plane, it may serve as a reference plane against which a photographic emulsion or a reticle may be placed. More often, the field flattener will be purposely spaced a short distance from the focal plane to keep dust and defects of polish from appearing on the optical image or to allow space for the use of a focal plane shutter, a calibration plate, a filter, etc. If the rear surface of the field flattener lies a distance greater than 0.15 F from the focal plane, it loses its corrective powers for field flattening purposes and becomes essentially an element of the optical system rather than a field flattener. Accordingly, the location of the field flattener may be defined by specifying that its rear surface lies on the long conjugate side of the focal plane by a distance varying from F to 0.15 F.

The field flattener may be a very weak spherical or aspheric lens used in the design of the main system as a final correction on a performance found satisfactory except for residual field curvature, or the field flattener may have an appreciable negative lens power for the purpose of helping to correct the basic Petzval curvature of field. If a field flattening lens has a variation in thickness at any point which exceeds a value equal, for example, to 0.04 F, the lens loses its essential character as a field flattener and becomes a strong element of the lens system. In general, if the field flattener is close to the focal plane and is made of a material of an average index of refraction, the maximum variation in focal displacement caused by variation in the thickness of the flattener is of the order of 0.015 F. For a focal length equal to 100 mm., a field flattener limited in variation of thickness to a maximum of 0.04 F produces a corrective power on field curvature of the order of 1.5 mm., which is in the normal range of the residual field curvature of optical systems for general use. Therefore, in order that the effect of the field flattening lens employed with objectives of the invention may be confined to field flattening, the variation in thickness of the lens must lie within the range from approximately 0 to 0.04 F. The lower limit of approximately 0 is used, because occasionally the aspheric correction on the field flattener may have an axial depth amounting to only a few waves of sodium light and, in the limit, the thickness of the field flattener may be used to efiect a final correction of small magnitude on distortion and astigmatism in the outer field.

Although, as shown above, the upper limit of the variation in thickness of the field flattener has been found to be 0.04 F, not all of this variation can properly be employed in the aspheric portion. The aspheric correction on the field flattener is employed for removing field curvature in the higher order terms, whereas any basic lens power of the flattener is immediately useful for reducing the Petzval sum with an added effect on the higher order terms. Accordingly, an upper limit of 0.02 F can be placed upon the aspheric variation of the field flattener, such limit referring to the maximum axial distance between the aspheric surface and a spherical surface with its center on the optical axis and passing through the vertex and the extreme extension of the aspheric surface.

substantially as follows:

Example III Lens Radil Thickn. 0 Glass nesses Types R I 0.635 I 1 =0. 075 1. 75510 47. 2 755472 R: 1.667 11 is =0. 007 1. 68900 30. 9 089309 Sr=0. 002 R 0.312 In i; =0. 050 I. 75510 47. 2 755672 S:=0. 020 R5 0.817 IV t =0. 013 1. 60500 37. 9 605379 S;=0. 200 Bl 0.399 v is =0. 013 1. 6203i 60. 3 620603 S =0. 020 R 0.909 VI ls =0. 054 1. 80370 41. 8 804418 S5=0. 002 Ru= 5.001 VII t =0. 007 l. 72000 29. 3 720293 Rrg= 0.435 VIII is =0. 075 l. 74 #50 i5. 8 745458 Se=0. 610 R15= 1318110 Ix [9 =0. 020 1.5l700 64. 5 H7645 R plnno The stop lies 0.1147 from vertex of R S =the back focal distance.

The surface of R is aspheric and is of such a shape that at 0.32 radian ofi-axis, the thickness reaches a maximum; at 0.42 radian ofi-axis, the thickness is approximately equal to the thickness at the optical axis. The maximum variation in thickness is approximately 0.011 of the focal length.

Then lens in Example I may be used, where necessary, without a field flattener, but a field flattener is employed if ideal results are to be obtained. In order that the lens may be used without the field flattener, it is so constructed that the astigmatic surfaces coincide over most of the field leaving only the zonal field curvature to be corrected.

I claim:

1. An objective for photographic purposes corrected for spherical and chromatic aberrations, including oblique spherical aberration, coma, astigmatism, field curvature, and distortion, which comprises a pair of outer components of net collective effect and a pair of components of net negative effect and of meniscus form disposed between the outer components and with their concave surfaces opposed to each other on opposite sides of a the vertex of R toward the central sto both collective components having an average index 0 refraction from 1.58 to 1.80 and the front collective component being of miniscus form with its inner air surface concave and of a dioptric power from 0.2 to -O.8, the said front collective component having at least one cemented surface curved away from the stop with the largest index difference across such a surface lying within the range 0.03 to 0.08 and being caused by a decrease in index in the direction of light travel while the rear collective component has a front air surface of a dioptric power from 0.3 to 0.4. said rear collective component having at least one cemented surface curved away from the stop, the negative meniscus components each including at least one positive and one negative element with the highest index of refraction of each positive element in each meniscus component exceeding the lowest index of refraction of each negative element of that component by at least 0.03 but less than 0.25, the

front negative meniscus component having a concave surface adjacent the stop of a dioptric power from l.7 to 2.8 and the dioptric power of a concave surface adjacent the stop of the rear negative meniscus component varying from L to 1.9 and having a numerical value less than that of said concave surface of the front negative meniscus component, all said dioptric powers being stated in terms of the net power of the entire objective taken as unity, the central air space separating said concave surfaces of the negative meniscus components having a length greater than 0.14 F and less than 0.28 F, F being the focal length of the objective.

2. The objective of claim 1, in which the largest index differences across the said curved cemented surface of the rear collective component lies within the range 0.01 to 0.06 and being caused by an increase in index in the direction of light travel.

3. The objective of claim 1, in which the front negative meniscus component has at least one negative element of an index of refraction smaller than the average index of the front collective component by a quantity lying within the range 0.02 to 0.15.

4. The objective of claim 1, in which the rear negative meniscus component has at least one negative element of an index of refraction smaller than the average index of the rear collective component by a quantity lying within the range 0.05 to 0.20.

5. The objective of claim 1, in which the largest index of refraction of the positive elements within the negative meniscus components is greater than the average index of each collective component but less than 1.85.

6. The objective of claim 1, in which the dioptric power of the front collective component as computed from the curvatures with the thicknesses neglected lies within the range 0.45 to 0.75 and the dioptric power of the rear collective component similarly computed lies within the range 0.75 to 1.10.

7. An objective for photographic purposes corrected for spherical and chromatic aberrations, including oblique spherical aberration, coma, astigmatism, field curvature, and distortion, which comprises a pair of outer components of net collective effect and a pair of components of net negative effect and of meniscus form disposed between the outer components and with their concave surfaces opposed to each other on opposite sides of a cent r a1 stop, both collective components having an average index of refraction from 1.58 to 1.80 and the front collective component being of meniscus form with its inner air surface concave and of a dioptric power from 0.2 to 0.8, while the rear collective component has a front air surface of a dioptric power from 0.3 to 0.4, said rear collective component having at least one cemented surface curved away from the stop, the negative meniscus components each including at least one positive and one negative element with the highest index of refraction of each positive element in each meniscus component exceeding the lowest index of refraction of each negative element of that component by at least 0.03 but less than 0.25, the front negative meniscus component having a concave surface adjacent the stop of a dioptric power from l .7 to 2.8 and the dioptric power of the concave surface adjacent the stop of the rear negative meniscus component varying from l.0 to l.9 and having a numerical value less than that of said concave surface of the front negative meniscus component, all said dioptric powers being stated in terms of the net power of the entire objective taken as unity, the central air space separating said concave surfaces of the negative meniscus components having a length greater than 0.14 F and less thin 0.28 F, F being the focal length of the objective, the outer collective components and the negative meniscus components between them forming a contiguous group and a field flattening lens lying outside the group and adjacent to and preceding the focal surface with the vertex of the rear surface of the lens spaced along the 12 optical axis from the focal surface by a distance ranging from 0 F to 0.08 F, the field flattening lens being aspheric on at least one of its air surfaces by an amount not exceeding 0.02 F in depth of departure of the aspheric surface from an imaginary spherical surface having its center on the optical axis and passing through the vertex and the extreme extension of the aspherie surface.

8. An ob ective having constructional data substantially as follows:

Lens Radll Thlckup I Glass masses Type:

R: II 1-667 11 :1 -0.007 1. 08900 30.0 089300 8 -0002 Rt" 0.312 111 at -0.050 1. 75510 47.2 750472 81-0020 Rs- 0.817 1v t1 0. 013 1 00500 37.0 305370 s=-0.200 R; --0.390 v 21-0013 1.02031 00.3 020003 B0 II -l.609

51-0020 Raw-0.000 vi n-0.054 1.80370 41.3 some Ss=0.002 Rn- 5.001 VII 11-11007 1.72000 20.3 720203 Rn- 0.43s VIII t. -0.075 1. 74450 45.8 745450 The stop lies 0.1147 from the vertex of R toward the *Ve'fFeYBf'Rij S =the back focal distance, R=radius of curvature for the optical surfaces, l=axial thickness of optical elements, S=axial separations between adjacent elements, n =indeX of refraction of the glass at the sodium line. v=reciprocal dispersion of the optical elements.

9. An objective having constructional data substan tially as follows:

Lens Radll Thtcb no I Glass nesses Types 8,-0.002 R4- 0.331 III ti -0.053 1.70065 47.8 701478 S -0.029 Rs= 0.960 IV t; -0.015 164900 33.8 649838 81 0.171 Re I 0.366 V ts -0.015 1.51868 64.2 519642 81-0-1117 R 0='-0.727 Vl is -0.061 1.70065 47.8 701478 Ss 0.002 R 2.170 VII 21-0006 1.68900 30.9 089309 Ris- 0.439 VIII ti -0.099 1.70065 47.8 701478 The stop lies 0.101 from the vertex of R toward the vertex of R S the back focal distance,

R=radius of curvature for theoptical surfaces, r=axial thickness of optical elements,

S=axial separations between adjacent elements,

13 n =index of refraction of the glass at the sodium line, v=reciprocal dispersion of the optical elements.

10. An objective having constructional data substantially as follows:

[F-LDOO f/2.5]

Inns Radlt Thickm; a Glass nesses Types s -0.002 R4- 0.312 III t; -0.050 1.75510 47.2 765472 5 -0020 Bn- 0.817 IV 34 -0.013 1.60500 37.9 605370 4-0020 R-0.909 VI t; -0.054 1.80370 41.8 804418 Ss-0.002 R1!- 5.001 VII 0.007 1.72000 29.3 720293 1211- 0.435 VIII 1| -0.075 1.74450 45.8 745458 Ru -(LQH 80-0640 Ruplsno IX is -0.020 1 51700 64.5 517045 Rnplane The at lies 0.1147 from the vertex of R toward the vertex of R Sq=th6 back focal distance,

The surface R is aspheric and is of such a shape that at 0.32 radian off-axis, the thickness reaches a maximum; at 0.42 radian off-axis, the thickness is approximately equal to the thickness at the optical axis. The maximum variation in thickness is approximately 0.011 of the focal length,

R=radius of curvature for the optical surfaces,

t=axial thickness of optical elements,

S=axial separations between adjacent elements,

n =index of refraction of the glass at the sodium line,

v=reciprocal dispersion of the optical elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,779,257 Lee Oct. 21, 1930 2,100,290 Lee Nov. 23, 1937 2,100,291 Lee Nov. 23, 1937 2,289,779 Herzberger July 14, 1942 2,550,685 Garutso May 1, 1951 2,559,881 Kingslake et a1 July 10, 1951 2,600,207 Cook June 10, 1952 2,622,478 Kleineberg et al Dec. 23, 1952 2,683,396 Klemt et a1 July 13, 1954 FOREIGN PATENTS 427,008 Great Britain Apr. 12, 1935