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Oct. .A_ J_ HQLMAN' ' OBJECTIVE FOR PROJECTION, ‘ PHOTOGRAPHY, TELEVISION, AND‘ FOR TELESCOPE Filed?ct, 30, 1940 - /§\\\\\\\\\\\\\\\\ Fig_ I/il’ 27/42 > Patented Oct. 29, 1946 2,410,069 semen rates rArsNr orrlcs 2,410,069 OBJECTIVE FOR PROJECTION, PHOTOGH v RAPHY, TELEVISION, AND FGR TELE SCOPE ‘ ' Arthur J. Holman, ‘East Orange, N. J. Application October 30, 1940, Serial No, 363,463 ' 4 Claims. 1 2 My invention relates primarily to that type of projecting apparatus, or camera, wherein the ?lm pletely new and original design requires con summate skill on the part of the designer. The reason why this is true is quite simple: prior to applicant’s discovery of the procedure herein after disclosed, there has never been any prac strip is moved continuously across the optical axis and the effect of this movement is so com pensated by means of moving optical rectifying elements .as to produce a stationary image. It has been the special object of my invention to ticalhmethod for setting up'a multiple element lens designby direct mathematical procedure. provide a proper stationary element to function with the single rotating lens Wheel having a plu rality of identical rectifying elements disposed symmetrically about its periphery as fully de scribed in Letters Patent of the United States No. 1,957,457 of May 8, 1934. My improved objec tive is essential to the realization of the best performance from the single revolving lens wheel rectifying system. Due to the distinctive fea tures of its design, the characteristics of my objective are such that it is suited admirably for use as a telescope objective. It‘also may be used to advantage, either singly or in pairs, as an objective in photography and for television. The distinctive features of my present design In present design practice the designer’s math ematical facilities have only provided means for 10 estimating the performance of a proposedlens element assembly after the curvatures and spac ings of the refracting surfaces have been set up. Heretofore the initial setting up of ‘the optical system has been based entirely on the experience and judgment, of the chief designer. In current practice this preliminary design is then turned over to the computing sta? for ray tracing trigonometrically; a process which, if done accurately and thoroughly, may consume several man years of effort. These computations yield de?nite and accurate data on spherical aberration, sine condition, achromatism, astig are twofold: ?rst, the relative curvatures of the matism of oblique ray bundles and other valu refracting surfaces are determined by an optical able ‘informationconcerning the probable per symmetry with respect to a radius and a point 25 formance of the optical, system. Generally the on the optical axis outside of the objective; sec initial setup is not good enough to meet the re ond, the relative thicknesses of the elements are quired lens performance and the chief designer, determined by an optical symmetry with respect perhaps with the assistance of his staff, deter to a point on the optical axis within the objec mines what modi?cations should be made in the tive. The focal length is the principal factor .30 initial lens setup to provide better performance. in determining the locationof the ?rst point on Again the computing staff analyzes the system the optical axis and the curvatures of the refract trigonometrically and again the chief designer ing surfaces determine the position of the sec examines the data and estimates how the lens ond point. Given the focal length and diameter, will probably perform if it is actually constructed. or the f value, of a proposed objective, and the 35 This procedure may go on through several set optical constants of the glasses to be employed, up modi?cations until the chief designer is satis it is a very simple matter to design my improved ?ed that the performance ‘of the lens will be objective. The method of calculation hereinafter sufficiently good to warrant building a sample. disclosed for designing an objective free from After the sample is‘ actually constructed as close the errors and design faults usually recognized 40 to speci?cations as is humanly possible, it is in optical computations, is the most elementary more often than not, found to be unsatisfactory on record, and both the method of calculation in performance and further computing is re and the lens design resulting therefrom are novel quired to determine which refracting surface or and most useful. My improved objective com surfaces should be changed in curvature or spac prises elements with spherical refracting sur~ ing or both to provide better performance from faces and its manufacture presents no new or the lens system. Current commercial practice in lens design requires genius in the chief de signer or inexhaustible patience in employing photographic or projection objective, as now “cut and try” methods plus very extensive ex practiced quite generally by skilled technicians, 50 perience in the art of lens design. presents a very di?icult and tedious task, par The primary characteristic of the design meth ticularly if the designer has no accurate per od herein disclosed, and also of the product so formance record from a former lens design which designed, is this ;' the optical system, whether it approaches closely the speci?cations to be met be for projection, photography, television or for a by the new design. To really fabricate a com .55 telescope, is integrated and built up from scratch dii?cult problems to the lens maker. The process of designing a modern high speed 2,410,069 4 3 as an original design about two cardinal points of the system, namely the optical center, or nodal point, and the point of principal focus. The design is de?ned entirely and completelyby 5 (1) the refracting power required, (2) the par ticular achromatism desired, (3) the optical char acteristics of the glasses employed,v and ?nally . cerned primarily with design features of the ?xed front component 4 and the combination of such component with the revolving lens wheel to form a complete and new optical rectifying objective. The values of T1 and m (Fig. 2), derived math ematically in the Letters Patent previously re ferred to, are such that: first, the lens will have, a speci?ed refracting power; and second, an arc described at radius R from center I!‘ will pass through point C at the intersection of the refract the optical center or nodal point of the system 10 by (4) the radius R to which the system is bent. The swinging end of radius R passes through and the pivoting end of radius R is centered on the optical axis of the systm at a, point closely related to and determined primarily by the point of principal focus. In all lens systems designed ing surfaces and also through point F which is the optical center of the lens. Values of T1 and r2 calculated in this manner determine a lens form which is bent to radius R around the point (1 lying on the optical axis outside of the lens. The in this manner, the ratios of the radii of curva 15 lens may therefore be de?ned as having an opti ture of the retracting surfacesare determined cal symmetry with respect to point 0 and radius ?nally by the radius R to which the system is bent and the spacing of each refracting sur face within/the system is determined completely and ?nally by the radius of curvature of each particular refracting surface in the system. The mathematics employed is'adequate to produce a ?nal design on the ?rst trial: nothing is left to R. 'The values determining this symmetry are, _ 1:32- an speculation or guess work; no ray tracing tri gonometric check is required because the opti cal system has been set up mathematically cor wherein rect. The design procedure is direct and the lens f is the focal length of the lens ‘structure resulting from this design procedure is 0 is (index of refraction of glass) —-1 really ‘new and differs fundamentally from lens is radius of bending of lens structures arrived at by the “cut and try” meth 30 R go is angle between optical axis and extreme posi ods‘, now generally employed. ' ' My device may be best understood by reference to the accompanying drawing in which Fig, 1 is an elementary elevation of an opti cal rectifying system showing rectifying elements carried by a rotating lens wheel, the stationary front component of the objective system and a section of the aperture unit and the ?lm strip tion of radius B- (Fig. 2) for values of (p less than 8 degrees, the follow ing approximations are very nearly correct and, because of their simplicity, are convenient for preliminary calculations: __ 2Rcf . "‘“R+¢j- _ 2Rcf “?nd thereon. v The design of a single element lens, such as Fig. 2 is a geometrical ?gure from which data 40 lens wheel element 3, is fully determined by the is obtained for calculating the relative curvatures above calculations 'forvalues of T1 and r2, except of the refracting surfaces of the lens'wheel ele for lens thickness which may have any value _ments, also the curvatures of the elements of the required by the mechanical structures without stationary front component. , Fig. 3 is, a cross section of a cemented triplet 4 changing its optical symmetry with respect to point 6 and radius R. ' wherein the optical center of the central ele The “design of an achromatic component or Qment coincides with the optical center of the complete achromatic objective involves the use of exterior surfaces of the complete objective. Fig, 4 is a cross section of a pair of cemented “triplets with a. diaphragm placed centrally be - tween them for photographic use or for use in television cameras. Referring now more specifically to the drawing, .in which like reference numerals indicate like parts, il(Fig. l) is the projector or camera ap erture unit, 2 is the ?lm strip suitably supported thereon and arranged to be operated at uniform velocity thereover, 3 indicates optical elements (three shown) carried by the revolving lens wheel and having their optical centers on a common circle described at radius R from the center ll of the lens wheel and 4 is the stationary compo nent which is commonly described as the front component of the objective system. The ele ments 3, are carried across the optical axis by rotation of the lens wheel, each in turn becom ing the rear component of the objective system and, when coacting with stationary front com morethan one kind of glass and at least two lens 50 elements, hence the simple calculations for bend ing ,a single element lens no longer provide a complete solution. An excellent achromatic tri plet, speci?cations for which are given hereinafter in a table, designed and built to operate as front " component ll in my revolving lens wheel projector, is an example of a multiple element objective having optical symmetry with respect to a point i) and radius R and having further optical sym metry with respect to a point F (Fig. 3) on the 60 optical axis and within the lens. This triplet consists of a crown element cemented between two flint elements, the latter being both made of the same kind of glass. The crown element is bent with respect to point i} F and radius R ‘as if it were surroundedby air. The interior surfaces of the flint elements con form to the curvatures of the adjacent crown surfaces so they may be cemented together. The exterior surfaces (radii T1’ and r2’) vof the ponent ll, completing the optical rectifying objec Complete data concerning the revolving 70 ?int elements are calculated .as if the flint . tive. lens wheel structures are disclosed in Letters Pat ent No. 1,957,457 hereinabove referred to, and reference thereto is hereby made ir lieu of fur ‘ ther description of the revolving structures. The ~ present application for Letters Patent is con elements were one piece and no crown element was imbedded therein. The ratio of refracting power of the positive crown element to the total 'refracting power of the negative ?int elements 75 is proportional to the V value of the glasses 2,410,069 5 employed. The V value for visual rays of a glass is 7Lp~1 ' ftp-7L1’! wherein no, ns, and no represent respectively the index of refraction for the D, F and C lines. The proper relation between refractive powers and V values is required, of course, to render the objective achromatic. The algebraic sum of the refracting powers of the elements is the refract ing power of the triplet. The calculations thus far have determined the curvatures of the sur faces. There remains only the determination of the proper thickness of elements to bring optical center F (Fig. 3) of crown element into exact register with optical center F of the com bined ?int elements. The distances a and b from optical center F (Fig. 2) to the refracting surfaces of a double convex lens are proportional to the radii of curvature of the surfaces. Thus 2_’l 17 T2 6 and spacings for the refracting surfaces. A lens system so designed will give optimum per formance. The mathematical conception of a single lens element bent to radius R around a point E3 on its optical axis may be’ stated as follows: The lens is so formed that its optical center F and the circle of intersection of its spherical refracting surfaces lie on the surface of an imaginary sphere of radius R centered on point 0. Furthermore, all points on the surface of this imaginary sphere, within the circle of intersection of the refracting surfaces of the lens, are distant from these spheri cal refracting surfaces in the ratio of 41/1) or 1‘1/1‘2. The foregoing is merely a statement of the geo metrical relationship existing between the curva tures of the refracting surfaces due to the fact that the lens is bent to radius R about the point B as illustrated in Fig. 2 of the drawing. The mathematical conception of the achromat ic triplet, which is the basic disclosure of the present application, may be stated as follows: The triplet comprises a crown element so formed that its optical center F and the circle of inter- - section of its spherical refracting surfaces lie on Employing this relationship and using T1 and 12 the surface of an imaginary sphere having radius (Fig. 3), the distance a is determined for the R centered on point 0, and two ?int elements so crown element. To this value a is added the formed and of such thicknesses that their joint center thickness of the thinner ?int element and optical center and the circles of intersection of the resulting value (1' together with T1’ and m’ (Fig. 3), is used to calculate b’. The value b 30 their internal and external spherical refracting surfaces lie on the surface of the imaginary sphere for the crown element subtracted from the value having radius R centered on point 0. Furtherb’ for the complete triplet gives the center more, all points on the surface of this imaginary thickness of the thicker ?int element. Thus the sphere within the circle of intersection of the thickness of each element has been determined and the exact position of the common optical 35 refracting surfaces of the crown element are dis tant from these refracting surfaces in the ratio center has been ?xed. A triplet built to these of (1/2) or ri/rz, and all points on the surface of dimensions is optically symmetrical both inter this imaginary sphere within the circle of inter nally and externally with respect to point t] and section of the exterior refracting surfaces of the radius R and moreover, the crown element and the combined ?int elements have a common opti cal center F. When the curvatures and thickness dimensions of the elements of such a triplet are drawn to ' scaie, we have the conditions shown in Fig. 3 wherein an arc of radius R described around cen ter 0 on the optical axis passes through F, the common optical ‘center of the central crown ?int elements are distant from these refracting surfaces in the ratio of a’/b’ or r1'/r2'. The fore going is a statement of the peculiar geometrical relationships existing between all refracting sur faces because of the bending of the lens and spac ing of the surfaces as illustrated in Fig. 3 of~the drawing. The ratio of refracting power of the crown element to the total refracting power of the ?int elements is proportional to the V values of the crown and ?int glasses. It is to be noted that the triplet design, wherein a crown element of lower refracting power is cemented between ?int elements of higher re fracting power, possesses one highly important advantage over other forms of lenses wherein ?int elements in this triplet are related in a a crown element of low refracting power forms very unusual and unique way: a way wherein an exterior surface. When the glasses of higher they would never have become related by accident refracting power form the glass-air surfaces, as or by any method of computation other than in Fig. 3, the radii T1’ and T2’ are longer, for a the method hereinbefore disclosed. There never given lens power, than they would be if a crown has been heretofore, any design of lenses or any method of computation which would make one 60 element formed a glass-air surface. Flatter ex terior surfaces contribute to a reduction in ?int element (front) so thin and the other ?int spherical aberration and therein lies one im element (rear) so thick as is illustrated in Fig. 3 element and of the combined ?int elements, and also through the point of intersection C’ of the crown refracting surfaces (extended) and through the point of intersection C” of the ex terior ?int refracting surfaces (extended). Obviously, the spherical surfaces of the crown and which is drawn to scale. The design procedure, as hereinbefore described, is straightforward and simple, consisting of two principal steps; ?rst, portant advantage of the present triplet design. Tests on several triplets designed in the fore going manner for widely varying applications calculation of the curvatures of the refracting have shown image quality heretofore unattain~ surfaces and, second, calculation of the spacing of able. -It is believed that the relatively simple each refracting surface from the nodal point of conceptions herein disclosed comprise all the the optical system. Any lens system calculated fundamental factors requiring consideration in in this manner possesses the geometrical relation 70 the design of a highly corrected objective. The ship of refracting surfaces, with respect to curva simple expedient of bending a triplet symmetri tures and spacings, which is peculiar to and cally with respect to a point on the optical axis characteristic of this design. The lens system exterior to the lens and proportioning the thick thus designed is mathematically correct: for its nesses of the elements to provide a common op type, there is no better combination of curvatures 75 tical center, i. e., providing optical symmetry 2,410,069 ~ 8 high speed distortion free photographic objec with respect to a point on the optical axis and within the lens, has eliminated entirely the la borious and tedious ray tracing method ofdesign tive or an objective of excellent quality for the television camera. Innumerable other applica tions of these design features will occur to those skilled in the art of lens design. The appended which often requires several man years of com puting to arrive at an approximate speci?cation .claims are drawn to cover any and all lens sys for a high speed photographic objective. Point 9, of course, always lies onthe optical axis of the lens, but radius R may vary somewhat tems wherein groups of elements and/ or the en tire system may possess-the optical symmetry herein speci?ed. depending upon the function to be performed Having thus fully described my invention, what by the particular lens. For example, in the re- 10 I claim is, volving lens wheel projector (Fig. 1) radius R. 1. A triplet comprising a central crown element for lens wheel elements 3, is the radius of the and a pair of ?int elements, said crown element circle whereon the optical centers of the recti having the radii of curvature of itsv two refract > fying lens elements are located in the lens wheel ing surfaces so related that said crown element assembly as more particularly described in Let- 15 meets the specification of being bent to radius ters Patent No. 1,957,457. In the case of a tele~ R. about a point ii on the optical axis of said scope objective, which is used normally for view triplet, said pair of ?int elements having the ing distant objects and is therefore focussed radii of curvature of its internal and external at or near in?nity, it is advisable to make R refracting surfaces so related that said pair of equal to or slightly greater than the focal length. 20 flint elements meets the‘ speci?cation of being In the case of objectives operating at ?xed focus bent also to said radius R about said point 0. B may be equal to the distance from the optical 2. A triplet comprising a central crown ele center of the lens to the plane of ?xed focus. ment and a pair of ?int elements, said crown ele The designer selects the radius of bending to ment having the radii of curvature of its two best suit the conditions whereunder the objec- 25 refracting surfaces so related that said crown tive is to function. element meets the speci?cation of being bent A typical triplet for use as front component ii, in my revolving lens Wheel optical rectifying objective, was built to the following speci?ca~ tions calculated as hereinbefore described: to radius R about a point ii on the optical axis of said triplet, said pair of ?int elements having the radii of curvature of its internal and external 30 refracting surfaces so related that said pair of ?int elements meets the speci?cation of being bent also to said radius R about said point 0, the external refracting surfaces of said ?int ele Diameter ___________________________ __ 2.375 Center thickness ___________________ __'_ .7Ll8 35 ments intersecting the optical axis of said triplet at points displacedfrom the nodal point of said R, equals ___________________________ __ 11.25 crown element inproportion to the radius of curvature of each of said external refracting sur Glass m; V faces of said ?int elements. Inches Focal length _________________________ __ o ____________________________________________ __ ____________________________________________ -_ Dimension r2 Grown 1. 5230 1.6228 Flint . Thickness ______________________________ .. 9.92 58 36.1 40 Flint . . 410 . 070 . 268 3. A triplet comprising a central crown ele ment and a pair of ?int elements, said crown element being so formed that its optical center F and the circle of intersection of its spherical refracting surfaces (extended) lie on the sur face of an imaginary sphere having radius R centered on point e, and said ?int elements being so formed and of such thicknesses that their joint optical center and the circles of inter section of their internal and external spherical refracting surfaces (extended) lie on the surface All linear dimensions are in inches. of said imaginary sphere, 4. An optical rectifying objective comprising While I have described in detail a cemented a plurality of identical lenses mounted on the triplet, it is obvious that many combinations of periphery of a lens wheel, said identical lenses elements and varieties of glass may be used in each having its principal focus at a common cen designing and constructing a lens’ system which ter on the axis of said lens wheel, the ratio of the may possess, either in its entirety or in groups radii of curvature of the refracting surfaces of of its elements, the optical symmetry with re each of said identical lenses determining a lens spect to a radius R and a point ii on the optical bent around said common center, and a multiple axis exterior to the system, and the optical sym metry with respect to a point F on the optical 50 element stationary front component wherein the ratios of the radii of curvature of the refracting axis within the system, which is the basic dis surfaces determine a. front component bent to closure of this application. A triplet, such as I radius B, said radius B being equal to the focal have described, used alone makes a most satis length of each of said identical lenses mounted factory telescope objective or a long focus photo graphic objective. A pair of these triplets sult- 65 on the periphery of said lens Wheel. ably spaced and provided with a centrally lo cated diaphragm (Fig. 4) makes an excellent ARTHUR J. HOLMAN.