# Патент USA US2406762

код для вставки1350-466 SR OR 294069762 SQ*- 3,1946# öeal’Cn H001 N y D. s. GREY 2, ,762 OPTICAL SYSTEM Filed June- 17,9, 1943 2 Sheets-Sheet 1 @if FIG. X266# ,_ 66. www y S¢Pt~ 3, 1946. _ D. s. GREY OPTICAL 2,406,762 SYSTE“ Filed June 19, v164e. I ' 2 sums-snm 2 MJ@ INVENTOR, BLOMmy ÖGBÍCÜ KOÜÍ , _ Patented Sept. 3, 1946 «- n 2,406,752 UNITED STATES PATENT OFFICE 2,406,762 OPTICAL SYSTEM David S. Grey, Cambridge, Mass., assigner to Polaroid Corporation, Cambridge, Mass., a cor poration of Delaware l Application June 19, 1943, Serial No. 491,493 14 claims. (Cl. 88-57) 2 This invention relates to optical systems and more particularly to athermalizatlon of optical ized to a predetermined extent for focal point by one glass lens; and systems comprising one or more lens elements of organic resin or plastic. In an optical system comprising one or more lens elements formed from an organic resin or Fig. 2 is a similar view of another lens system wherein a plurality of plastic lenses are substan tially completely athermalized for focal point by a, glass lens. In accordance with the present invention, a system of lens elements, such as a photographic plastic, changes in temperature produce varia tions in the index of refraction, curvature, and thickness of each plastic lens and thereby change the position of the focal surface of the system. It is inconvenient and frequently impractical to rc-focus the lens system to correct for these thermal effects, and accordingly, it is one object of the present invention 1to provide a novel optical system comprising one or more plastic lenses, 15 objective, wherein a plurality of the elements are formed of plastic, may be athermalized for focal point by providing the system with one or more glass lens elements. To accomplish this an equa tion similar to the achromatization equation for the focal point is utilized in the lens computation and an infinite nu value is assigned tothe glass lens the lenses of said system being selected and ar or lenses and a convenient iìnite nu value, for ex ranged in a novel manner. so that there is no ample 100, to the plastic lenses in said equation. The athermalization is thus achieved with the glass serving as the "thermal crown” and the appreciable variation in focal point due to changes in temperature. Another object is to provide a novel arrange 20 plastic as the “thermal ilint.” Such an equation ment of, and a novel method of arranging lens thus involves an expression for thermal nu value, elements in an optical system wherein all but instead Jof color nu value 0r dispersion as in the the first are formed from en organic resin and the case of achrornatization. Specifically, the ther ñrst is of glass and athermalizes the entire sys mal nu value for a material may be determined tem for focal point. 25 from the reciprocal of the quantity A fui-.ther object is to provide a novel ather malized system of lens elements wherein a plu rality of lenses subject to appreciable tempera ture effects are athermalized for focal point to a predetermined extent by one or more lens ele 30 wherein n is the index of refraction of the ma ments of a material negligibly affected by terial, C'r is the coefficient of linear expansion of changes in temperature, as for example one of the material and the optical glasses. Still another object is to provide a, novel opti ¿a dT cal system comprising one or more glass lens ele 35 ments and a plurality of plastic lens elements is the rate of change of the index of refraction wherein athermalization of the vplastic elements of the material with change in temperature, it is achieved lto a desired extent by the glass ele being noted that the factors involved are prop ment or elements in a manner analogous to the erties inherent to a material. As will presently achromatization of a lens system for focal point. 40 appear, the plastics or “thermal flint” materials 'I'he above and other objects and novel features described herein have similar coeñlcients of linear expansion as well as similar rates of change in of this invention will more fully appear from the index per degree centigrade and hence will have following detailed description when the same is similar thermal nu values. This athermalization read in connection with the accompanying draw ings. It is to be expressly understood, however, 45 is approximated if the glass lens elements are constructed so that the sum of the “convergence that the drawings are for purposes of illustration factors” of said elements is equal to approxi only and are not intended as a definition of the mately the power of the lens system, i. e., if the limits of the invention, reference being primarily had for this latter purpose to the appended ` claims. In the drawings: Figure 1 is a sectional View of a lens system embodying one form of the invention wherein a plurality of plastic lenses are partially athermal sum of the convergence factors of the plastic ' 50 lenses is equal to approximately zero. The con vergence factor is the product obtained when the power of each of said glass elements is multiplied by a position factor (1-C’)2, C being the frac tional convergence of the paraxial ray on reach 55 ing said element. If .the above condition is satis 3 2,406,7651 ned, athermalization for focal point is approxi mately obtained regardless of the number of glass lenses in the system and regardless of the loca tion of said lensesl relative to the plastic elements of the system. It will be appreciated that when only a, single lens element of glass is employed the power of that element multiplied by the position factor for that element should be approximately equal in temperature, is (l00-N)% and the system is thus completely athermalized for focal point. Referring to the drawings,` there is shown inFig. 1 a photographic objective comprising a plu rality of plastic lens elements and athermalized Ain accordance with the present invention. In the form shown, said objective comprises live lens components, I, II, III, IV, and V, wherein foremost lens component‘I is the athermaliza to the power of the entire system. 10 tion lens and is formed preferably of crown glass, It is preferable in optical systems, because of such as Crown 1. The remaining lens elements the lesser expense, to utilize as many elements of of the system are formed preferably of two suit plastic as possible, and accordingly, it is prefer able organic resins or plastics which have the able wherever possible to athermalize a lens sys necessary differences in indices of refraction and tem comprising plastic elements for focal point 15 nu values .to constitute flint and crown mate by a single lens element of glass. It is also de rials for the system. A satisfactory resin for the sirable, because of the greater hardness of Ithe crown material is cyclohexyl methacrylate, which glass as compared to the plastic, to use the glass has an index of refraction (ND) of approximate element as the outside or ñrst lens of the system 'ly 1.506, a color nu value or dispersion (Vl of so that said glass element serves as a protection 20 approximately 57, a. coefficient of linear expan for the remaining elements of the system. With sion of 7.6 X 10-5, a rate of change in index of this arrangement of lenses in a given optical sys refraction of _0.000131 per degree C for the so tem, i. e., a ñrst glass lens and remaining lenses dium D line and in the illustrated system lenses of plastic, it is possible, according to the present II, IV, and V are formed of this material. For the invention, to athermalize the system by selecting 25 flint material styrene, which has an index of re the glass element so that the focal length there fraction (ND) of approximately 1.592, a color nu of is approximately the same as .that of the total value or dispersion (V) of approximately 31, a lens system. coeñîcien-t of linear expansion of 7.1 X 10-5, and The athermalization obtained in the above a rate of change in index of refraction of manner, i. e., by having the sum of the converg 30 _0.000136 per degree C for the sodium D line, ence factors of the athermalization lenses equal may be employed, and lens III is formed of this -to the power of the system, approximates a com material. plete or 100% athermalization for focal point for Lens I has a power equal to approximately 4/=, the plastic lenses. The thermal effect on the that of the system and, accordingly, provides ap other lenses in the system, i. e., the athermaliza 35 proximately 80% athermalization for focal point tion lenses, is negligible, and accordingly, there of plastic lenses II to V, the system being de is obtained substantially 100% athermalization signed for a housing which is adapted to provide for the entire system. ` ' the additional 20% athermalization necessary to It may be desirable, however, to obtain some achieve substantially complete athermalization lesser or greater percentage of athermalization 40 for focal point. by means of the athermalization lenses because In Fig. 2 there is illustrated a photographic there may be a partial compensation for, or a objective comprising six lens components, IA, IIA, greater variation in, temperature effect on focal IIIA, IVA, VA, and VIA wherein the foremost lens point due to other causes than the thermal ef IA is formed of an optical glass, such as dense fects on the lenses of high thermal coefficient. 45 barium crown, lenses IIA, IVA, VA, and VIA are For example, the linear expansion or contraction formed of cyclohexyl methacrylate and lens IIIA with temperature of the housing for the lens sys is formed of styrene. In this system lens IA has tem may partially athermalize for focal point. a power equal to approximately that of the sys Accordingly, to obtain a substantially complete tem, i. e., 98% of the power of the system, so that over-all athermalization for the lens system, it 50 lenses IIA to VIA are substantially entirely ather may be necessary to obtain, by means of the malized for focal point by said glass lens. athermalization lenses, an athermalization Although styrene and cyclohexyl methacrylate which differs from 100%. In this connection it are preferred, it is to be understood that the has been determined that the percentage ather plastic lenses may be formed of any resins which malization obtained by the athermalizíng lenses 55 are sufñciently transparent, homogeneous and is in direct proportion to the ratio of the sum of hard, to be used optically, and preferably those the convergence factors of the athermalizing which may be accurately cast by polymerization lenses to the power of the optical system. As a in molds. Example of further resins of this result, when .thermal effects, for example, on the character are me thyl methacrylate, benzyl housing of a lens system cause a partial ather 60 methacrylate, phenyl methacrylate, and ortho malization or correction of N % forl the change in chlorostyrene. The vinyl compounds, such as focal surface with temperature, the athermaliz ing lens elements may be arranged and com- ’ styrene, orthochlorostyrene, and other members of «the styrene family and esters of acrylic and puted so that the sum of the convergence factors alpha-substituted acrylic acids, and particularly thereof is such that the ratio of said sum to the 65 of methacrylic acid, provide polymerizable mate power of the system is equal to rials best suited for forming the plastic lenses. In each of the tables below relating to the illus 100 trated lens systems, the column “Radius” refers to 100 the radii of the spherical surfaces as measured in 70 the same linear units as used to measure the~ times the power of the system. Thus, the focal length of the system illustrated, as for ex amount of athermalization Iobtained optically, l. e., by means of lenses having substantially zero coefûcient of thermal expansion and having their ample, millimeters. The column designated “Thickness” refers to the thickness of the lenses, also the air gaps between lenses as measured on optical properties affected negligibly by- changes 75 the axis of the lens system in the same linear QUCII bil “UU 2,406,762 5 umts as those vused to measure the “Radius.” 'I'he letter "t" indicates lens thickness and the letter "d" air spaces, d10 in the nrst table being the distance from Re to the focal surface, and du in the second table being the distance be.-Y tweenRu and the focal surface. The term “Nn” is used to designate the index of refraction of the materials for the lenses as measured for the yellow “D" line of a sodium arc. The column “V” designates nu value ND-l Np-Nc i. el.î reciprocal dispersion, for the lens materials use . ' The following table sets out the constructional _ [Focal Length=l90l Radius I _______________________ __ Thickness R1=+120.1 t1=13.8 Rn=-1,848 5 dz=0 II ...................... -_ R3=+75. 2 ì3=35. 0 R¿=+44. 7 d4= 15. 8 R5= _67. 3 ls=4. 5 III ..................... -_ Nn 1.523 l. 506 ' t1--46. 2 R1=-107.4 t9=19. 2 that lens, where C is the fractional convergence of a paraxial ray incident on said lens. Since certain changes in carrying out the above process and in the constructions set forth which 10 embody the invention may be made without de parting from its scope, it is intended that all matter contained in the above description, or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting 15 sense. \ 1. 592 31 57 material negligibly subject to thermal effects and having a predetermined index of refraction, dis 1. 506 57 persion and a power which is related to the power da=0. 0 V ...................... _l Rs=+218. 8 of a lens is to be understood to mean the product of the position factor (l-C)2 and the power of " 1. 506 Rs=~l-71. 1 IV _____________________ _. Rß=+71.1 ' In the claims the term "convergence factor” It is also to be understood that the following claims are intended to cover all of the generic and speciñc features of the invention herein de scribed, and all statements of the' scope of the V 20 invention which, as a matter of language. might be said to fall therebetween. What is claimed is: 57 1. A method of forming an athermalized lens 57 system, comprising, providing a. lens element of data for the lens system of Fig. 1: Lens erties substantially unaffected by >changes in tem perature within ordinary limits. of the systemmäs’a’"vwhölëî'bptically correcting said element negligibly subject to thermal effects 'I'he above photographic objective has an f/4.5 30 for at least one aberratign`with_„a_ plurality of Ro=-114.0 d1n=140.7 aperture and is well corrected over a 40 degree total ñeld. The following table sets out the constructional components apprecfably‘subjeéiîíô thermal effects each selectedlto lhaveapproximately equal ther mal nu values and a predetermined index of re fraction, dispersion‘and a power related to the 35 power of the system as a whole, and arranging said components appreciably subject to thermal effects and said element negligibly subject to Nn V thermal elïects in axial alignment at spacings which satisfy the condition that the sum of the 1.611 58.8 .40 convergence factors of said components appre data for the photographic objective of Fig. 2: [Focal Length=l001 Lens IA _____________________ ._ IIA .................... _. IIIA.. .................. _IVA.. .................. -_ Radius Rx=+48.24 h=7.6 Rz=+452. 49 d2=0 R3=+33. R4= - 153. 84 R4==-l53.84 R5=+27.85 t3=14. 8 1.506 57 i|=1. 8 d5=4. 6 1. 591 31 , ta=l.8 1.506 57 1. 506 57 1. 506 57 R¢=-66.22 R1=+46. 30 VAH .................. __ VIA ................... -_ Thickness ì d1=6. 95 I~7s=+l69. 49 R9= -- 106. 38 Rm=+88. 8S is=5. 0 dc= 0 l1o=6. 0 R11=-74.07 dl1=66- 1 ciably subject to thermal effects approximately equals zero while the convergence factor for said element negligibly subject to thermal effect ap proximates the power of the system. 2. A method of forming an athermalized lens 45 system, comprising, providing a plurality of lens elements of material negligibly subject to ther mal effects and each having a predetermined index of refraction, dispersion and a power which The above photographic objective has an f/3 aperture and is well corrected over a 35 degree 50 is related to the power of the system as a whole, optically correcting` said elements negligibly sub-> total field. ject to thermal effects for at least one aberration There is thus provided a novel system com with a plurality of components appreciably sub prising a. plurality of lens elements of organic ject to thermal effects each selected to have ap resin or plastic and one or more athermalizing lens elements of glass, said elements being ar 55 proximately equal thermal nu values and a pre determined index of refraction, dispersion and a ranged in a novel manner to eifect a predeter power related to the power of the system as a mined degree of athermalization for the system. whole, and arranging said components appreci A novel method is provided for selecting ather ably subject to thermal effects and said elements malization elements whereby the sum of their convergence factors bears a predetermined rela 60 negligibly subject to thermal effects in axial alignment at spacings which satisfy the condi tioned relation to the power of the system in tion that the sum of the convergence factors of accordance with the degree of athermalization said components appreciably subject to thermal for focal point for the plastic lenses which is eiïects approximately equals zero while the con desired. Although the invention is primarily directed to 65 vergence factor summation for said elements negligibly subject to thermal enects approximates the athermalization of lens systems of plastic, it the power of the system. is not limited thereto and is applicable to any lens system comprising a plurality of components hav 3. A method of forming a lens system having ing coefficients of thermal expansion of such mag .N percentage of athermalization for focal point, ‘ nitude that changes in temperature will produce 70 comprising, providing at least one lens element an appreciable variation in the back focal length. of material negligibly subject to thermal effects To athermalize a system in accordance with the and having a predetermined index of refraction, dispersion and a power which is related to the invention, the lens element or elements which are used to athermalize need only have negligible power of the system as a whole, optically correct thermal expansion and have their optical prop 75 ing all such elements- negligibly subject to ther 2,406,752 7 8 7. Alens system predeterminedly athermalized' mal effects for at least one aberration with a plurality of components appreciably subject to thermal effects each selected to have approxi for focal point, comprising, a lens element ot glass having a predetermined index of refraction, mately equal thermal nu values and a predeter mined index of refraction, dispersion and a power related to the power of the system as a whole, dispersion and a power which is related to the power of the system as a whole, and at least one lens of plastic which optically corrects the sys and arranging said components appreciably sub ject to thermal eil'ects and all such elements negligibly subject to thermal eiïects in axial alignment at spacings which satisfy the condi 10 tion that the convergence factor summation for all such elements negligibly subject to thermal effects approximates the power of the system multiplied by N/ 100. tem for at least one aberration and which has a predetermined index of refraction, dispersion and a power related to the power of the system as a whole, all such plastic lenses having approxi mately equal thermal nu values, and said lenses being arranged in axial alignment at spacings with respect to each other to satisfy the condition that the product of the power of said glass lens 4. A method of forming an athermalized lens l15 and its position factor forms a ratio with the power of the system which is directly proportional glass having a predetermined index of refrac to the degree of athermalization for focal point desired for the system. ` tion, dispersion and a power whicl'i- is related 8. A lens system predeterminedly athermalized to the power of the system as a whole, said glass system, comprising, providing a lens element of lens element being negligibly‘subject to thermal 20 for focal point, comprising, at least one lens ele ment of glass of a predetermined index of re effects, optically correcting „said glass element for at least one aberration' with a plurality of lens components of plastic appreciably subject to thermal effects, each plastic element being se fraction and dispersion and a power which is related to the power of the system as a whole and a plurality of lens components of plastic optically lected to have an approximately equal thermal 25 correcting the system for at least one aberration and having predetermined indices of refraction, nu value and a predetermined index of refrac dispersion and individual powers related to the tion, dispersion and a power related to the power power of the system as a whole, all such plastic of the system as a whole, and arranging said plas components having approximately equal thermal tic components and said glass element in axial alignment at spacings which satisfy the condi 30 nu values, and said elements and components being arranged in axial alignment at a spacing tion that the sum of the convergence factors of with respect to each other to satisfy the condi the plastic components approximately equals zero tion that the sum of the products obtained by while the convergence factor for said glass ele multiplying each such glass element by its posi ment approximates the power of the system. 5. A method of forming an athermalized lens 35 tion factor forms a ratio with the power of the system which is directly proportional to the de system, comprising, providing a plurality of lens gree of athermalization for focal point desired for said system. 9. A lens system athermalized for focal point, is related to the power of the system as a whole, said glass lens elements being negligibly subject 40 comprising, at least one lens element of material negligibly subject to thermal effects and having a to thermal eiîects, optically correcting‘said glass elements of glass each having a predetermined index of refraction, dispersion and a power which elements for at least one aberration with a plu rality of lens components of plastic appreciably subject to thermal effects, and each selected to ` predetermined index of refraction, dispersion and a power which is related to the power of the sys tem as a whole, and at least one lens component ~. have an approximately equal thermal nu value 45 of a material appreciably subject to thermal effects which optically corrects the system for at and a predetermined index of refraction, dis least one aberration and has a predetermined persion and a power related to the power of the index of refraction, dispersion and a power re system as a whole, and arranging said plastic lated to the power of the system as a whole, all components and said glass elements in axial alignment at spacings which satisfy the condi tion that the sum of the convergence factors of 50 such lens components appreciably subject to thermal effects having approximately equal ther mal nu values, said lenses being arranged in axial alignment at spacings with respect to each other while the convergence factor summation for said to satisfy the condition that the sum of the con glass elements approximates the power of the sys tem. 55 vergence factors of all such lenses negligibly sub ject to thermal eifects approximates the power of 6. A method of forming a lens system having N said system. percentage of athermalization for focal point, 10. A lens system havingN percentage ather comprising, providing at least one lens element of malization for focal point, comprising, a fore glass having a predetermined index of refrac tion, dispersion and a power which is related tc 60 most lens of glass having a predetermined index of refraction, dispersion and a power of approx the power of the system as a whole, each such imately N/ 100 times the power of the system, and glass element being negligibly subject to thermal a plurality of plastic lenses optically correcting effects, optically correcting all such glass ele the glass element for at least one aberration and ments for at least one aberration with a. plurality of plastic lens components appreciably subject 65 each having approximately equal thermal nu values and a predetermined index of refraction, to thermal effects and each selected to have an dispersion, and a power related to the power of approximately equal thermal nu value Aand a pre the system as a whole, said plastic lenses being determined index of refraction, dispersion and a the plastic components approximately equals zero power related to the power of the system as a axially aligned with said foremost glass lens at ' whole, and arranging said plastic lens compo 70 spacings which satisfy the condition that the sum cf the convergence factors of the plastic nents and said glass lens elements in axial align lenses approximates the product of ment at spacings which satisfy the condition that the convergence factor summation for all such glass lens elements approximates the power of the system multiplied by N/100. ' l-N . 100 and the power of the system. lib. Urncs oearCn Hoof 2,406,762 r 10 of the-system', in combination', at least one lens of glass having a predetermined index ci.' refrac-A tion, dispersion and a power related to the power> 11. An athermalized optical system, comprising, a, foremost lens element of glass which has a pre determined index of refraction and a predeter mined dispersion and which substantially pro of the system as a whole, and a plurality of plas vides the power of the system, and a plurality of tic lenses each having an approximately similar thermal nu value and a predetermined index of refraction, a dispersion and a power related to- components 0f plastic which optically correct the glass element for at least one aberration, said plastic components having approximately similar the power of the system as a whole, said glass and thermal nu values and each of said components plastic lenses being axially aligned andmounted having a predetermined index of refraction, dis 10 within the housing to have the convergence factor persion and a power which is related to the summation for all such glass lenses approximately power of the system as a whole, and said glass equal to element and said plastic components being axially 100-N aligned at spacings such that the sum of the 100 convergence factors of said plastic components is approximately zero while the convergence fac times the power of the system whereby to ather tor for said glass element approximates the power malize the system by (100-N) %. of the system. 14. A method of athermalizing for focal point a 12. A partially athermalized lens system hav lens system having at least one lens element of ing lens means comprising at least one glass lens 20 glass of predetermined index of refraction, dis of predetermined index of refraction, dispersion persion and a power related to the power of the and a power related to the power of the system system as a whole and a plurality of lens com as a whole, and a plurality of plastic lenses N% ponents of plastic which optically correct each athermalized for focal point by such glass lens such glass lens element and which each have ap means and optically correcting the glass lens 25 proximately similar thermal nu values and a pre means, said plastic lenses having approximately determined index of refraction, dispersion and a equal thermal nu values and each having a pre power related to the system as a whole, compris determined index of refraction, dispersion and ing, arranging each said glass lens element and plastic lens components in axial alignment with whole, all said lenses being arranged in axial 30 each other at spacings to satisfy the condition a power related to the power of the system as a that the sum of the products obtained by multi plying the power of each said glass element by its position factor equals approximately the power alignment at spacings such that the sum of the' convergence factors of the plastic lenses is ap proximately equal to 100-N < 100 )% of the system multiplied by 35 of the power of the system while mounting said components in a housing of 13. In a lens system having a plurality of glass a. character which provides the system with N % and plastic lenses mounted in a housing which 40 athermalization for focal point. provides N% athermalization for the focal point DAVID S. GREY. _ 88. @F111 ¿5,17 - » _ Certiñcate of Correction Patent No. 2,406,7 62 <`-`~~- September 3, 1946 DAVID S. GREY It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: o lineseffects; 60 and 61, strike out “relationed”; column 6, line 43, for the WordColumn “effect” 5,read and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oñìce. Signed and sealed this 6th day of June, A. D. 1950. [am] THOMAS F. MURPHY, Assistant Uommz'm'oner of Patents. Certificate o! Correction Patent No. 2,406,762 y _ _ ~ “ September 3, 1946 DAVID S. GREY It is hereby certilìed that errors appear in the printedspeciñcation of the above numbered patent requiring correction as follows: linesefects; 60 and 61, strike out “relationed”; column 6, line 43, for the wordColumn “effect”5,read and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 6th day of June, A. D. 1950. [BILL] THOMAS F. MURPHY, ¿insistantl Oammíasz'oner of Patents.

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