# Патент USA US3045556

код для вставки' United States Patent 0 ” CC 3,045,546 Patented July 24, 1962 2 1 the convergent front member comprises a plurality of 3,045,546 convergent components of which at least one is a doublet FOCAL LENGTH component having a dispersive internal contact surface and at least one is a simple component, whilst the di OPTICAL OBJECTIVES OF VARIABLE Gordon Henry Cook, Leicester, England, assignor to Tay vergent second member comprises a plurality of divergent lor, Taylor & Hobson Limited, Leicester, England, a components of which at least one is a doublet component having a collective internal contact surface and at least British company Filed Sept. 29, 1958, Ser. No. 764,006 Claims priority, application Great Britain Oct. 2, 1957 14 Claims. (CI. 88-57) This invention relates to an optical objective for photo graphic or other purposes, having relatively movable one is a simple meniscus component whose rear surface is convex to the front and has radius of curvature not 10 less than 0.33)‘; and not greater than the range of axial members, whereby the equivalent focal length of the ob— jective can be varied at will, whilst maintaining good correction for the various aberrations. movement of such divergent second member, where f2 is the equivalent focal length of such second member. in one arrangement of such objective, the convergent front member comprises a simple convergent component located in front of a convergent doublet component Desirable features in such an objective include a wide whose front surface is convex to the front with radius range of continuously variable focal lengths, constant of curvature between 0.5f1 and 1.0f1 (where fl is the equivalent focal length of the convergent front member), focussing position throughout the range, constant relative aperture throughout the range at any setting of the dia phragm, a short distance ‘from front vertex to focal plane, simplicity of construction to minimise loss of light by absorption and reflection and also to reduce weight, and focussing for near objects independent of focal length. All these desirable features have been attained by the invention forming the subject of United States of America patent speci?cation'No. 2,649,025, according to which the objective comprises an axially movable divergent at least one simple meniscus component in the divergent second member having its rear surface convex to the front with radius of curvature not less than 0.5f2. In an alternative arrangement, the convergent front member comprises a convergent doublet component lo cated in front of a simple convergent component whose front surface is convex to the front with radius of curva ture between 0.4f1 and 0.813. The internal contact sur face in such doublet component is preferably convex to the front with radius of curvature between 0.41‘, and member located in front of a stationary convergent rear 09h, the mean refractive index of the material of the member and behind an axially movable convergent front 30 front element of such doublet component exceeding that member, wherein in each operative position the equiva of the rear element thereof by between 0.05 and 0.15. lent focal length of the divergent combination of the In either of such arrangements, the radius of curvature front two members bears to that of the complete objec tive a ratio between 8 and 13 times the reciprocal of the vergent front member is preferably greater than 1.511, f/number of the objective, the virtual image of a distant . whether such surface is convex or concave to the front. of, the rear surface of the front component of the con object formed by such divergent combination having a Preferably, the ratio of the equivalent focal length of constant axial position relatively to the stationary rear member throughout the range of variation of the equiva the divergent combination of the front two members to the equivalent focal length of the whole objective lies lent focal length of the objective, the complete objective between 3 and 8 times the reciprocal of the f/ number of being corrected for spherical and chromatic ‘aberrations, 40 the objective. coma, astigmatism, ?eld curvature and distortion through The equivalent focal length h of the convergent front out the range of variation. member preferably lies between 1.0f2 and 1.67)‘; times the It should be made clear that the terms “front” and value of the expression (l+\/Q), where Q is the ratio “rear” are herein used in accordance with the usual con of the value of the upper limit of the range of variation vention to relate to the sides of the objective respectively 45 of the equivalent focal length of the complete objective nearer to and further from the longer conjugate. to the value of the lower limit'thereof. In this case, the The present invention has for its object to effect im ratio of the equivalent focal length of the complete ob provements in the variable focus objective of such prior jective at the lower end of the range of variation thereof patent, especially in respect of its optical properties, and > to the f/number of the objective lies between 0.27;‘2 and more'particularly, whilst still attaining the desirable fea 50 0.565. tures above mentioned, to achieve increased relative aper The rear component of the divergent second member ture and increased angular ?eld of view and at the same preferably consists of a divergent doublet component time to enable the objective to focus on objects closer to whose internal contact surface is collective and convex the camera. These improved optical properties render to the front with radius of curvature between 0.66)‘, and 'the objective according to the present invention highly 55 1.55, the mean refractive index of the material of the suitable, not only for exterior use at relatively great ob rear element of such doublet component exceeding that ject distances, but also for studio photography or cine of the front element of such component by between 0.15 matography or television photography. and 0.3. Preferably, the divergent second member com The objective according to the present invention is prises two divergent simple meniscus components in front corrected for spherical and chromatic aberrations, coma, 60 of a divergent doublet component, and has axial length astigmatism, ?eld curvature and distortion throughout the between 0.613 and 1.313. range of variation, and comprises an axially movable di Preferably, the ratio of the equivalent focal length f_-, of the stationary rear member to the equivalent focal vergent member located in front of a stationary con length of the complete objective at the lower end of the vergent rear member and behind an axially movable con vergent front member, wherein throughout the range of 65 range of variation thereof lies between 1.25 and 2.5\/Q, variation the ratio of the equivalent focal length of the and such ratio may also conveniently lie between 0.2 and divergent combination of the front two members to the 1.2 times the f/number of the objective. equivalent focal length of the complete objective remains The Petzval sum for all the surfaces of the stationary constant and the virtual image of a distant object formed rear member may conveniently lie between 0.3 and 4.0 by such divergent combination has a constant axial posi 70 times the equivalent power of such member. _ tion relative to the stationary rear member, and wherein Conveniently, the diaphragm of the objective is located 3,045,546 3 4 at or near the front surface of the stationary rear mem Thus, the Petzval sum for all the surfaces of such ber, and the diameters of the front two members are made larger than is necessary to accommodate the full axial beam. This ensures that the diaphragm will always be the effective aperture stop of the system and that the angle of the cone of light from the rear member to an rear portion preferably is positive and lies between 0.25 and 0.85 times the reciprocal of the equivalent focal length of the complete objective at the lower end of the range of variation thereof. For distortion compensation, at least one of the four air-exposed surfaces of such rear axial image point will remain constant throughout the portion should preferably be both collective and strongly convex towards the diaphragm. For oblique colour com range of variation, and therefore that the relative aper ture of the objective will remain constant throughout such pensation, such rear portion preferably includes at least range for any one setting of the diaphragm. 10 one internal contact between a convergent element and Focussing for near objects is preferably effected by a divergent element, the Abbé V number of the material of such convergent element exceeding that of such di axial-movement of the convergent front member inde pendently of the second and third members. vergent element by at least 20. It should be made clear Conveniently, with the above described objective, use-. ful alternative arrangements thereof may in some cir cumstances be obtained by replacement of one stationary rear member by another, the front two members re maining unaltered. For this purpose, the lens mount housing the objective may conveniently be providedwith that the term “internal contact” as used therein is in tended to include both an internal cemented contact sur face and a broken contact, that is, a contact formed be tween two surfaces differing by so little in curvature that the contact can be assumed for all practicable purposes to have a radius of curvature equal to the harmonic mean means whereby two or more alternative rear members of the radii of curvature of the two surfaces forming such can be selectively attached to the mount in the correct broken contact. In the case when two alternative rear members are pro vided for use with the same pair of movable front mem bers, the rear member associated with the higher f/num position relative to the front axial movable members. It should also be mentioned that it is often practicable, with a given example of the above described objective, for such example to be scaled proportionally to suit different ranges of variation of the equivalent focal length of the complete objective, the range of variation of angu ber and with the range of higher equivalent focal lengths may consist of two convergent portions separated from one another by an air space whose axial length is greater lar ?eld covered by the objective remaining approximately than the equivalent focal length of either of such por tions. For example, the front portion may consist of a the objective. 30 convergent doublet component, whilst the rear portion Again, for example in the case of two differently sized widely spaced therefrom may consist of two convergent television cameras having different sensitivities and whose doublet components. ranges of variation of equivalent focal length are related Four practical examples of variable focus objective ac by a scaling factor of say 2.5, it may happen that it will cording to the invention will now be described by way suffice for the objective of the larger camera to have of example with reference to the accompanying drawings, an f/number about 2.5 times the f/number of that of in which the same in such scaled variants, as also the f/ number of the smaller camera. In such case, it is possible to utilise the same two front members for both cameras, but with FIGURE 1 shows one example of variable focus ob jective suitable for use in the smaller of the above-men different rear members, giving ranges of focal length and tioned television cameras, as well as for other uses, also f/numbers related by the same factor, say 2.5, but 40 FIGURE 2 shows one example of variable focus ob both covering approximately the same range of angular jective suitable for use in the larger of such television ?eld. A typical example of this is for a television camera having a f/ 1.8 objective with equivalent focal length varying from 2.25 to 8.0 centimetres, and a second tele vision camera having an f/4.5 objective with variation of equivalent focal length from 2.25 to 8.0 inches. . A further possibility is, by substitution of a different rear member, to give, in any position of adjustment of the front members, an increased equivalent focal length of the objective, without change of image size, and there fore with reduced angular ?eld. Widely different types of rear member may be em ployed, but in general it is important for the rear mem ber to have the correct Petzval sum dependent on that of the front two members, and to provide the correct compensation for the residual distortion and oblique colour aberrations of the front two members. Such dis tortion and oblique colour compensation can most effec tively be provided by suitable choice of the parts of the cameras, as well as for other uses, FIGURE 3 shows a further example which may be used in the smaller television camera, and FIGURE 4 shows a fourth example which may be used in the larger television camera. Numerical data for the example of FIGURE 1 are given in the following table, in which R1, R2 . . . rep resent the radii of curvature of the individual surfaces counting from the front, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, D1, D2 . . . represent the axial thicknesses of the various elements, and S1, S2 . . . rep resent the axial air separations between the components, the table also giving the mean refractive index nd for the d-line and the Abbé V number of the material used for each element. The table also gives the clear diameters for the air-exposed surfaces of the objective. rear member furthest from the diaphragm of the objec 60 The insertion of equals (=) signs in the radius columns of the tables, in company with plus (+) and minus (-) tive, which as above mentioned is preferably located near the front surface of the rear member. Thus, the Petzval sum for all the surfaces of the rear member preferably lies between 0.35/1‘, and 0.7/f2, and may also lie between 0.7 and 1.4 times the positive value of the equivalent power of the divergent combination of the front two members in the position of adjustment corresponding to the lower end of the range of variation of the equivalent focal length of the objective. Usually, the stationary rear member will include at least six air-exposed surfaces, and the rear portion of such- member, having the rear four of the air-exposed surfaces, is especially important in connection with the residual aberrations of the front two members. signs which indicate whether the surface is convex or concave to the front, is for conformity with the usual Patent Office custom, and it is to be understood that these signs are not to be interpreted wholly in their mathematical signi?cance. This sign convention agrees with the mathe matical sign convention required for the computation of some of the aberrations including the primary aberra 70 tions, but different mathematical sign conventions are required for other purposes including computation of some of the secondary aberrations, so that a radius indi cated for example as positive in the tables may have to be treated as negative for some calculations as is well under< stood in the art. 3,045,546 5 6 Example I R2 in this doublet component is dispersive and convex to the front with radius of curvature equal to 0.609)‘;, [Equivalent focal length varying from F0=1.000 to Fm=3.555. Relative the difference between the mean refractive indices of the materials of the two elements of this component being ‘0.11. The rear surface R3 of such doublet is slightly concave to the front with radius of curvature equal to aperture 171.8] Radius Thickness or Refractive Air Separation Index m Abbe V Number Clear Diameter 3.85f1. R1 =+ 7. 5120 3 984 D1 =0.1693 1. 7618 26. 98 D2 =0. 7902 1.651 58. 60 R1 =+ 3. 2319 R: =-20.4139 3.721 S, =0.0056 R4 =+ 2.9246 3.248 D; =0. 3612 1. 651 58.60 R, =+ 4.7196 3.113 S2 =0. 0564 to 1.9995 R5 =+ 1.7611 1.795 D4 =0.1129 1.62344 56.22 R1 =+ 1.0395 1.524 S3 =0. 2484 Rs =+ 2. 9246 1.510 D5 =0.1129 1. 62344 56. 22 Re =+ 1.6104 1.377 S4 =0. 5757 Rm=— 1. 7367 1. 156 De =0. 0903 Rn=+ 1.3767 1. 51507 56. 35 1. 7618 26.98 I D1 =0. 2145 R1z=+ 7.2263 D! =0. 2484 1. 717 tween the front two members is increased to the maximum 0.986 member from its initial position to increase the equiva lent focal length F of the objective from its minimum 0.960 value F0 is given by the expression fz(F—-Fo)/\/FmFo, 0.835 ‘and the forward movement of the front member from its S6 =0. 2484 R15=— 1.1519 Rlt=— 0.6037 R11=+ 1.1519 D9 =0. 2484 1.723 37. 99 Dw=0. 1242 1. 64793 33.80 1. 6935 1.005 It will thus be seen that the front member at ?rst moves 1.063 forward and then back again, returning to its initial posi tion again when F reaches its maximum value Fm. The 53. 39 R1u=-— 1.5956 Ss =0. 3951 R1u=+ 1.4933 Rn=— 0.9178 initial position is given by the expression 0.805 S7 =0. 3048 R1a=+ 5.9011 D11=0. 2484 air space S2 between the front two members has its lowest value 0.0564F0, whilst the air space S5 between the rear two members has its highest value 2.1124150. When the objective is to be adjusted to increase its equivalent focal length, the middle member is moved backwards towards the stationary rear member until in the position of maxi mum focal length Fm the air space S5 has been reduced to O.l693Fo, and at the same time the air space S; be value 1.9995130. The backward movement of the middle 46.0 R14=-— 5.9011 > 1.072 S5 =2.1124 to 0.1693 R13=+ 1.1519 10 ’ The semi-angular ?eld covered by the objective varies from about 191/2 degrees at minimum equivalent focal length F0 to about 51/2 degrees at maximum equivalent focal length Fm. In the position of adjustment giving the lowest value F0 of the equivalent focal length of the objective, the 1.209 Du=0. 5080 1. 6968 55. 61 D1s=0. 1129 1. 70035 30. 28 most forward position of the front member occurs when F'q/FmFo so that ‘at the time the front member has ad vanced (as indicated at c) by about 0.59F0, from its initial position. In this way the overall length of the ob jective is kept short throughout the range of variation. In this example, the equivalent focal length f1 of the During these movements the conjugate, distances of convergent front member in front of the air space S2 is 40 the middle member (that is the distances from its nodal 5.3067150. The equivalent focal length f2 of the divergent points of the image of the object formed by the front second member between the air spaces S2 and S5 is _ member and of the virtual image of such image formed 1.4337F0 so that the ratio of F0 to the f/number of the by the middle member) vary; the ratio of such conjugate objective is equal to 0.3913. The equivalent focal length distances being the magni?cation produced by the middle )3 of the convergent stationary rear member behind the member. Thus, if M0 and Mm are the values of such air space S5 is 1.6917Fo so that the ratio fa/Fo is equal magni?cation corresponding respectively to the minimum to 0.94 times the f/number of the objective. ' and maximum focal lengths F0 and Fm, then The equivalent focal length of the divergent combina Mm/ M02Fm/ F0 tion of the front two members varies between 2.8143170 and 10.0065Fo. The ratio of this focal length to the The arrangement is such that this magni?cation passes equivalent focal length F of the whole objective remains through unity when FWFmFO, so that in fact constant throughout the whole range of variation and is equal to 2.8143, which is 5.0657 times the reciprocal of the f/number, 1.8, of the objective. Since the virtual image of the object formed by the The ratio f1/f2 is 3.701, which is 1.283 times the ex combination of the front two members occupies the same pression (1+\/Q), where Q is equal to Fm/Fo and Fm/Fo position relatively to the stationary rear member in all is 3.555. It will be noticed that the ratio f3/F0 is greater positions of adjustment (that is, the algebraic sum of the back focal length of this combination and the separation than 1.25 and less than 2.5\/Q, that is 4.714. The divergent second member between the air spaces 60 between the middle member and the rear member re mains constant in all positions), such image in the ex S2 and S5 consists of two simple meniscus divergent com ample being 4.8573F0 in front of the surface R13, the po ponents located in front of a doublet divergent component, sition of the image thereof formed by the stationary rear whose internal surface is collective with radius R11 equal R”: m 1. 119 member likewise remains the same, so that the image to 0.9615, the difference between the mean refractive indices of the materials of the two elements of this doublet 65 plane A of ‘the whole objective remains ?xed in position throughout the adjustment, the back focal distance a from being 0.247. The radii of curvature of the rear surfaces R7 and R9 of the two simple components are respectively 0.7251‘2 and 1.123f2. The range of movement of this divergent member is l.943lFo. The overall axial length of this member between the air spaces S2 and S5 is 1.3547F0 or 0.945192. the rear surface R20 to such image plane A being 1.1056Fo. The size of the image however increases as the equivalent focal length increases, and the ratio of the maximum image size to the minimum image size is clearly. equal to Fm/Fo. In the foregoing description of the movements, it has The convergent front member consists of a convergent been assumed that the object position remains unchanged, doublet component in front of a simple convergent com for example at in?nity, and it will be clear that for a ponent whose front surface R4 is convex to the front with radius equal to 0.5 5 1 f1. ' The internal contact surface 75 ?xed object position the resultant image position remains 3,045, 546 7 8 ?xed, the effect of the adjustments being to_alte?r__the___s_ige also equal to 0.532/f2 and to —-l.04 times the equivalent power of the divergent combination of the front two members, at the lower end of the range of focal length variation, such power being —0.3554/F0. v_lf_t_h_e imageJ'l'fT however, the object position changes;~ a furtl?adj'ustment will be necessary in order to retain; the same resultant image position for all object positions]; This can be simply achieved by an additional movement of the front member independgngiluo_f_ the mlddw rear meglhers/ Taking'th'e position (or ~faMthTé'FFETnge of The individual Petzval curvatures of the surfaces of the rear portion of the stationary rear member (such rear portion comprising a convergent simple component fol lowed by a convergent doublet component) are respec positions) of the front member corresponds to an in ?nitely distant object as the standard, the necessary fur tively for R18 +0.069/Fo, for R19 +0.257/Fo, for R20 ther adjustment of the front member for focussing for 10 +0.275/F0, for R21 —0.00l/F0 and for R22 zero, so that a near object consists of a forward movement of such member through a distance equal to f12/ (ll-f1) , where d is the distance of the object in front of the front nodal point of the front member in its position of adjustment. Since the Petzval sum for this rear portion is 0.6/F0. The sur face R20 is both collective and strongly convex to the front and contributes largely towards compensation of the residual distortion error of the front two members. this expression is independent of the equivalent focal 15 The Abbé V number difference across the cemented sur length F of the whole objective, it will be clear that with each and any additional adjustment of the front member to suit a particular object distance, the main movements to vary the focal length and alter the image size can still be effected without altering the resultant image position. face R21 in the doublet component amounts to 25.33, and thus contributes largely towards compensation of the residual oblique colour error of the front two members. Numerical data for the alternative example of variable focus objective shown in FIGURE 2 are set forth in the following table. This arises from the fact that in any one position of the Example 11 middle member, the additional movement of the front [Equivalent focal length varying from F0: 1.000 to Fm: 3.555. member to suit object distance is such that the image of Relative aperture 174.5] the object formed by the front member always occupies the same position relatively to the middle member. In 25 other words, throughout the whole range of both adjust ments, the position of the virtual image of the object formed by the combination of the front two members remains constant relatively to the stationary rear member. Radius R1 =+2.9578 The two movements can readily be eifected by a suitable 30 R1 =+1.2724 mechanism interlinking the movement of the middle R3 =—8.0370 member with that of a carriage on which the front mem R4 =+1.1514 ber is adjustably mounted. In order to maintain constant relative aperture through out the range of movement and also to avoid objectionable 35 vignetting of the oblique rays, the clear diameters of all the surfaces of the front two members are made greater than is necessary to accommodate the full axial beam for all settings of the iris diaphragm, which thus alone de termines the relative aperture in all positions of adjust ment. In the example, the iris diaphragm is located 0.0564170 in front of the surface R13 and has maximum diameter of 0.952170. The clear diameters of the indi vidual surfaces in the example are speci?ed in the table of data given above, these values being well in excess of 45 the full diameter of the axial beam. Thus, for instance, Thickness or Refractive Abbe V Air Separation Index n4 Number Clear Diameter 1. 569 D1 =0.0667 1.7618 26. 98 Dz =0.3111 1.651 58. 60 1.465 51 =0.0022 1.279 Ds =0.1422 1. 651 58.60 Rs =+1.8581 1.226 Sr =0.0222 to 0.7872 R6 =+0.6933 R1 =+0.4093 D4 =0.0444 1.6234 56. 22 0.707 0.600 83 =0.0978 Rt =+1.1514 0.594 D: =0.0444 1.6234 56.22 R9 =+0.6340 ' 0. 542 S4 =0.2267 R1o= -0.6837 R1|=+0.5420 0. 455 De =0.0356 1. 5151 56.35 D1 =0.0844 1.7618 26.98 Rn=+2.8450 0. 388 S5 =0.8316 to 0.0667 Rit=+1.5650 the maximum diameter of the axial beam at the surface R14=—0.4601 R1 varies during the adjustment from 0.556Fo to 1.976Fo, Rr5= —0.8424 0.388 D; =0.1333 1.5151 56. 35 Do =0.0667 1. 7283 28.66 0. 405 st =2.1112 the clear diameter of such surface being 3.984150. At R.t=+2.3003 0~ 984 D1o=0.2222 1. 5075 61.16 the surface R5, whose clear diameter is 3.1l3F0, the axial Rn=—1.0337 beam diameter varies from 0.494Fo to 1.752F0. For the Du =0.0667 1.70035 30. 28 Ris=-4.3350 1. 014 surface R6, having clear diameter 1.795F0, the axial beam S7 =0 diameter varies from 0.487130 to 0.997Fo.v For the sur Rm=+0.8386 , > 1.041 D12=0.2667 1. 5097 64. 44 face Rm, having clear diameter 1.072F0, the axial beam Rz0=—2.3003 . 55 diameter varies from 0.544F0 to 0.930Fo. D1a=0.0667 1. 70035 30. 28 Rzr=+9.8290 _ 0.986 In this ?rst example, the stationary rear member has four components, of which the ?rst is simple and conver In this second example, the iris diaphragm B, which gent, the second is a divergent doublet, the third is simple has a maximum diameter 0.381F0, is located 0.0222Fo in ‘ and convergent and the fourth is a convergent doublet. The objective is well~corrected throughout the range of 60 front of the front surface R18 of the rear member, and the virtual image of the object formed by the divergent variation for the usual primary aberrations and also for combination of the front two members is located 1.8901F0 secondary aberrations. It is to be appreciated, however, in front of the diaphragm. The back \focal distance a that the number and arrangement of the components of from the rear surface R21 to the image plane A is 0.596Fo the rear member may be considerably modi?ed, inde and remains constant in all positions of adjustment. The pendently of the two front members, according to cir semi-angular ?eld covered is the same as in the ?rst cumstances. example, varying from 191/2 degrees at minimum equiva In the above example, the Petzval sum for the surfaces lent focal length F0 to 51/2 degrees at maximum equiva of the movable convergent front member is +0.116/F0, lent focal length Fm. The equivalent focal length f1 of that for the movable divergent second , member the front member is 2.0892130 and that of the divergent is --0.447/F0, that for the stationary convergent rear second member f2 is 0.5644Fo, so that the ratio of F0 to member is +0.371/F0, and that for the complete objec tive is +0.040/F0. Since the equivalent power of the rear member is 0.591/Fo, its Petzval sum is 0.63 times such power. The Petzval sum of the rear member is the f/number in this example is 0.3913. The equivalent focal length f3 of the stationary rear member is 3.1585 F0, so that the ratio fa/Fo is equal to 0.713 times the f/num ber of the objective. 3,045,546 10 for the smaller camera. In the ?rst example above de As in the ?rst example the ratio f1/f2 is 3.701 or 1.283 (l+\/Q). The ratio fa/Fo is again greater than 1.25 and less than 2.5\/Q, Q being again equal to 3.555. The ratio of the equivalent focal length of the divergent scribed, where the equivalent focal length f; of the rear member is materially smaller than the combined equiv alent focal length of the front two members, when the rear member of the objective is replaced by an alternative rear member whose equivalent focal length is about 2.5 times that of the rear member given in the table, without combination of the front two members to that of the whole objective is again constant and is equal to 1.108, which is 4.986 times the reciprocal of the f/ number (4.5) of the objective. altering the front two members, the minimum and maxi , mum equivalent focal lengths of the two alternative com In the example of FIGURE 2, the rear member com prises two widely spaced convergent portions, the front 10 plete objectives thus obtained are respectively related by a factor of approximately 2.5, the angular ?elds covered by the two objectives are the same and the f/numbers of the two objectives are related by a factor of approxi mately 2.5. Now if the data in the second table above set forth are scaled up by a factor of about 2.5, it will be realised that the data given for the front two members two portions of the rear member are each less than the become identical with that given for the front two mem axial air space between them. _ bers in the ?rst table, so that the examples of FIGURES The individual Petzval curvatures of the surfaces of 1 and 2 constitute two alternative complete objectives of the rear portion of the rear member are respectively, for above-described kind, the rear member of the second R1‘, 0.146/F°, for R17 -o.073/F0, for R18 +O.095/F0, 20 the example being and alternative rear member for the same for R1,, +0.403/F0, for R20 —O.032/F0, and for R21 front two members. The two alternative complete ob— —0.042/Fo, so that the Petzval sum forlall the surfaces . jectives are respectively suitable for use in the two televi of such rear portion is positive and equal to 0.497/Fo. sion cameras above mentioned, the objective of the ?rst The Petzval sum of the whole rear member is positive and equal to 0.958/Fo, which equals 0.540/7‘2 or 1.07 times 25 example being suitable for the smaller camera and the ob jective of the second example being suitable for the the equivalent power (0.903/F0) of the divergent com larger camera. _ \bination of the front two members in the minimum focal The following table sets for the numerical data for length position. The surface R19 is both collective and the rear member of Example II in terms of the same basic strongly convex towards the diaphragm of the objective and thus largely contributes towards compensation for 30 unit as the table for Example I, i.e. the minimum equiv alent focal length F0 of Example I. the residual distortion error of the front two members. portion consisting of a convergent doublet component having equivalent focal length 1.38%, whilst the rear portion consists of two convergent doublet components, whose combined equivalent focal length is 1.52F0. It will ‘be noticed that the equivalent focal lengths of the 15 The Abbé V number difference across the cemented sur face R1», is 30.88 and that across the cemented surface R20 is 34.16, such differences, especially the latter, largely con Radius Thickness or Refractive Abbe V Air Separation Index nd Number Clear Diameter tributing towards correction of the residual oblique colour S5 =2.1124 to error of the front two members. The movements of the front two members are the same as those described for the ?rst example but on a reduced scale, the maximum forward movement of the front member being indicated at 0 (‘approximately 0.241%) whilst the front and rear surfaces of the divergent second member in its rearmost position are indicated by broken lines. It will be observed that the components of the ?rst and second members in the second example are arranged 0.1693 Rl3=+ 3.9752 0.985 D; =0.3387 1. 51507 56. 35 DD =0.1693 1. 72830 28. 66 Ru=~ 1.1687 Rl5=-‘ 2.1397 ' 7 . 1.028 SB =5.3625 Rm=+ 5.8428 2.500 Dw=0.5645 R11=-— 2.6255 D11=0.l693 R1s=~1l.0l09 - 1. 50749 61.16 1. 70035 30. 28 ‘ 2. 576 S7 =0 in the same manner as in the ?rst example, and further more that the radii of curvature of individual surfaces of Rm=+ 2.1301 the front member have the same relationships with the equivalent focal length f1 of such member in each exam ple, as have also the radii of curvatures of surfaces in R21=+24.9657 _ 2. 645 Di:=0.6774 1. 50970 64. 44 D1a=O.1693 1. 70035 30. 28 R2o=— 5.8428 2. 504 the second member with the equivalent focal length f2. 50 The data in this table completely describes the alterna It will be clear that the objective in either of the two tive rear member for the objective of Example I, which is above-described examples may be proportionately scaled suitable for the smaller television camera, to provide an dimensionally to suit various requirements. For exam alternative objective suitable for the larger television ple, the objective in either example may be scaled dimen~ camera. It will be clear that in‘ these alternative objec sionally to have a minimum equivalent focal length F0 of 55 tives, the rear members are not related simply by a scaling 1 centimetre and a maximum equivalent focal length Fm factor since, when one of such rear members is dimen of 3.555 centimetres, or alternatively the objective may sionally scaled, its degree of aberration correction is also be scaled so that F0 is equal to 1 inch and Fm is equal similarly scaled, whilst the requirement is that the aber to 3.555 inches. In the former case, the ?gures in the ration correction aiforded by each rear member should table for such example are indicative of measurements in 60 be the same since the alternative objectives employ iden centimetres and in the latter case such ?gures are indica tical movable members and the aberration corrections of tive of measurements in inches. The scaling factor for the rear member must compensate for the residual aberra-> the complete objective in this instance is 2.54, that is, the tions of the front members. One advantage of modifying ratio 1 inch to l centimetre. When the complete objec the rear member only of the objective for the smaller tive is scaled in this manner not only the angular ?eld 65 camera to suit the larger camera is that the larger camera covered by the objective remains unaltered, but also the f/number of the objective is unaltered. will be able to focus on objects equally as close to the camera as will the smaller camera, whereas the scaling up of the whole objective results in a corresponding scaling It may sometimes be the case, for example with two differently sized television cameras having different sensi up of this minimum focussing distance. It will be ap tivities, that in addition to such cameras requiring variable 70 parent in the above described circumstances, that instead focus objectives whose minimum and maximum equiv of providing two complete objectives, one for each cam era, it may often be convenient to provide interchange able rear members in the mount housing the movable example of approximately 2.5, the larger camera need members, such complete mount being suitable for use in only be provided with an objective having an f/number of about 2.5 times the f/number of the objective needed 75 either one of the cameras. For convenience, FIGURES alent focal lengths are related by a scaling factor, for 3,046,546 11 1 and 2. have been drawn to scales which make the size of the front two members the same in each ?gure in order to make clear the interchangeability of the rear In this example, the back focal length a from the sur face R22 to the rear focal plane A of the objective is l.3577F0. The iris diaphragm B is located as near the members. front surface R13 of the rear member as is practicable. This means that in terms of the minimum equivalent focal ‘length F0 respectively of Examples I and II, the scale of FIGURE 2 is approximately 2.5 times the scale of FIGURE 1 since the minimum equivalent The equivalent focal length h of the convergent front member in front of the air space S2 is 5.5227170. The equivalent focal length f2 of the divergent member be focal length F0 of such examples are related by this tween the air spaces S2 and S5 is 1.4338F0 factor. ratio of F0 to the f/number (1.9) of the It should be mentioned, however, that when the rear 10 0.365f2. The equivalent focal length is of member of one objective is replaced by another rear gent stationary rear member behind the air member, so as to give an alternative objective having an 1.4649Fo so that the ratio fa/Fo is equal to increased equivalent focal length (in any position of ad justment of the front members) and approximately the same angular ?eld, the Petzval sum of the rear member should not be reduced and the ratio of such sum to the equivalent power of the rear member will therefore in crease in approximately the same proportion as the increase in the equivalent focal length. Conversely, a so that the objective is the conver space S.,, is 0.771 times the f/number of the objective. The equivalent focal length of the divergent combina tion of the front two members varies between 2.9291F0 and lO.4l46Fo. The ratio of this focal length to the equivalent focal length F of the Whole objective remains constant throughout the whole range of variation and is equal to 2.9291, which is 5.565 times the reciprocal substitution of a more powerful rear member to provide 20 of the f/number (1.9) of the objective. an alternative objective of reduced equivalent focal length would reduce such ratio. In a further variant of either of the above described complete objectives, the equivalent focal length of the whole objective may be increased, in any position of ad justment, by appropriate change of rear member, without changing the image size. This results in smaller angular ?elds of view and in these circumstances it is permissible to reduce the Petzval sum of the whole objective or to make such sum negative. Small changes of this kind can be achieved by merely scaling the rear member and mak ing relatively minor dimensional changes to re-balance the aberrations. A further example of variable focus objective is shown in FIGURE 3 and numerical data for such example are given in the following table, Example III that is 4.714. ' The divergent member between the air spaces 8,, and S5 consists of two simple meniscus divergent components located in front of a doublet divergent component, whose internal contact surface R11 is collective, the radii of 30 curvature of the rear surfaces R7 and R9 of such simple components respectively being equal to 0.823f2 and 0.81813. The range of movement of this divergent mem ber is 1.943130. The convergent front member consists of a simple convergent component in front of a conver gent doublet, whose internal contact surface R4 is dis persive. The front surface R3 of the doublet component of the front member has a radius of curvature equal to 0.68413. Equivalent focal length varying from F0=1.0O0 to Fm=3.555. Relative aperture f/1.9] Radius The ratio fl/fg is 3.851, which is 1.335 times the expression (1—|—\/Q), where Q is Fm/FO which equals 3.555. It will be no ticed that f3/F0 is greater than 1.25 and less than 2.5\/ Q, Thickness or Refractive Abbé V Air Separation Index 11.1 Number Clear Diameter . The semi-angular ?eld covered by the objective in the example of FIGURE 3 varies from about 191/2 degrees at minimum equivalent focal length F0 to about 51/: de grees at maximum equivalent focal length Fm. The movements of the two front members follow the same general laws as those for the ?rst example de R1 =+ 6.2363 4.144 D1 =0. 3584 R, =+22. 0600 1. 6510 58.60 ' 4.095 Si =0. 0036 R3 =+ 3.7771 3. 794 D2 =0. 1433 1. 7484 27. 85 D; =0. 7885 1. 6510 58. 60 R4 =+ 2.1724 R5 =+12. 1838 3. 319 S2 =0.0358 to 1. 9790 R5 =+ 1.7767 ' D4 =0. 1076 1. 7200 1.816 50. 31 R1 =+ 1.1802 1.588 S; =0.2151 Ra =+ 1.9188 1. 515 D5 =0.1076 1. 7200 D5 =0. 0860 1.5076 61.16 D1 =0. 2151 1. 7484 27.85 0.858 by an additional movement of the convergent front mem 0.823 ber alone, the arrangement being such that the image plane remains in the same position for all object dis adjustment. Focussing on near objects is again effected 0. 0364 Rl3==+ 0.9260 1. 7170 47. 90 R14=—27. 9977 85 =0. 2267 R1s=— 1.0929 ' 0.722 D9 =0.1693 1.7230 37.99 D1o=0.0948 1. 6535 33. 48 R1s= - 0.5385 R11=+ 0.9452 0.696 S1 =0. 1037 R|s=+ 8. 4198 0.844 Dii=0. 0903 1. 7003 30. 28 D12=0. 3386 1. 6910 54. 80 R?=+ 0. 9935 Rzu=-— 1.4814 1.019 Si =0. 0034 Rz1=+ 1.2972 1.109 D13=0. 1919 R2Z= —46. 1968 highest value, and the air space 8,, decreases from its 1.146 S5 =1.9796 to D5 =0. 2171 The maximum forward movement of the front member is indicated at c and is about 0.591%. During this move ment the air space S2 increases from its lowest to its namely 4.655F0 in front of the surface R13, in all posi tions of adjustment, so that the image plane A of the‘ whole objective remains ?xed in position throughout the R1|=+ 1. 3227 R1z=+ 8.8900 50 and then moves back again to its initial position. 1- 224 1.349 S4 =0. 5018 Rm=— 1.5832‘ moves backwards toward the stationary rear member, while the convergent front member at ?rst moves forward highest to its lowest value. The virtual image of the object formed by the front two members occupies the same position relatively to the stationary rear member, 50.31 Rn =+ 1.1716 scribed, so that during the variation of the equivalent focal length of the objective-from its minimum value F0 to its maximum value Fm, the divergent second member 1.6910 54. 80 1. 099 tances. As mentioned in connection with the ?rst example, in order to retain constant relative aperture throughout the range of movements and also to avoid objectionable vignetting of oblique rays, the clear diameters of all the surfaces of the front two members are made greater than is necessary to accommodate the full axial beam for all settings of the iris diagphram, which thus alone determines the effective aperture in all positions of ad justment. Thus, in the example of FIGURE 3, the maxi— 75 mum diameter of the full axial beam respectively at the 3,045,546 13 14 front surface R1 and at the rear surface R5 of the front member varies from 0.526F0 to 1.871Fo and from virtual image formed by the combination of the front two members is located 1.833F0 in front of the dia phragm. The back focal length a from the surface R20 to the rear focal plane A of the objective is 0.9118F0. 0.446F0 to 1.594F0 during the movements, but the actual clear diameters of these surfaces R1 and R5 are respec tively 4.144Fo and 3.319130. The maximum diameter of 5 1.816F0 and 1.146F0. As shown in FIGURE 3, the stationary rear member has four components of which the ?rst is simple and con vergent, the second is a divergent doublet, the third is a convergent doublet and the fourth is simple and con The angular ?eld covered is the same as in Example 111, varying from about'19l/z degrees at minimum equiva lent focal length F0 to 51/2 degrees at maximum equiva lent focal length Fm. The equivalent focal length f1 of the convergent front the axial beam respectively at the front surface R6 and at the rear surface R12 of the middle member varies from 0.441F0 to 0.903F0 and from 0.482Fo to 0.831110, the actual clear diameters of these surfaces R6 and R12 being 10 member is 2.1743F0 and that of the divergent second member is 0.5 645E) so that the ratio of F0 to the f/num ber (4.8) is 0.36913. The equivalent focal length )3 ofv the stationary rear member is 1.4555F0 so that fa/Fo equals 0.303 times the f/number of the objective. vergent. The objective of the example is well-corrected 15 The ratio of fl/fz is 0.385, the same as in the ex throughout the range of variation for the usual primary ample of FIGURE 3, whilst the ratio of f3/Fo is again aberrations and also for secondary aberrations. greater than 1.25 and less than 2.5\/6, where Q is In this third example, the Petzval sum for the surfaces equal to F,,,/ F0 which equals 3.557. of the movable convergent front member is 0.1l1/F0, that The Petzval sum of the rear member is positive and for the movable divergent second member is —0.450/F0, 20 equal to 0.9827/Fo or 0.555/f2, whilst the individual that for the stationary convergent rear member is 0.354/F0, and that for the complete objective is 0.015/F0. Petzval curvatures of the surfaces of the rear portion of the rear member are respectively, for Rm —0.037/F0, The Petzval sum of the rear member is thus 0.52 times fO-r R17 for R18 for R19 its equivalent power, or —1.04 times the equivalent power +0.284/F0 and for R20 zero, so that the Petzval sum for of the divergent combination of the front two members 25 such rear portion is 0.436/F0. at the lower end of the range of focal length variation. The movements of the front two members in Example Such Petzval sum is also equal to 0.507/1‘2. IV are the same as those described for Example II, the The individual Petzval curvatures of the rear portion maximum forward movement of the front member being I of the rear member are respectively for R18 0.049/F0, approximately 0.24F0 as indicated at c, and the front and rear surfaces of the divergent second member in its 30 for and R19 for —0.003/Fo, R22 0.009/F0, £01‘soR20that the Petzval fOl' R21 sum for all rearmost position being indicated by broken lines. surfaces of such rear portion is 0.646/F0. As with Examples I and II, it will be realised that if A fourth example of variable focus objective is shown the data for the fourth example are scaled up by a factor in FIGURE 4 and numerical data for such example are of approximately 2,5, the data for the front two members set forth 111 the following table. 35 are identical in each of Examples III and IV, so that the rear member of FIGURE 4 constitutes an alternative rear Example IV member for the same two front members, the scales of FIGURES 3 and 4, in terms of the minimum equivalent [Equivalent focal length varying from Fo=1.000 to Fm=3.557. Relativ aperture f/4.8] Radius focal lengths F0 respectively of Examples “III and IV, Thickness or Refractive Abbé V Air Separation Index nd Number Clear Diameter 40 being related in the same manner as those of FIGURES l and 2. The complete objective of FIGURE 3 is thus suitable for use in the smaller of the television cameras Ri=+2.4552 D1=0.1411 R2=+8.6850 1. 6510 58. 60 R4=+0.8553 Ri=+-1.7968 Dr=0.0564 1. 7484 27.85 Da=0.3104 1. 6510 58. 60 D4=0.0423 R1=+0.4646 Ds=0.0423 Ro=+0.4613 1. 7200 50. 31 De=0.0339 R1i=+0.5207 0.715 1. 7200 60. 31 1. 7484 Ru=— 1.1286 60. 42 Ds=0.0444 1.7000 41. 18 R1s= —-0.9453 Ds =0. 2821 1. 5190 60. 42 D9 =0. 1129 1.7000 41. 18 0.840 0.869 1. 390 Dl0=0- 1693 1. 6258 35.74 Dii=0. 3950 1. 5097 04. 44 Ri7=+ 1. 6123 ~ 0. 331 1. 5190 Diameter R15: —26. 2462 0. 451 Da=0.l111 Clear Number 85 =1. 8057 27. 85 ‘ Abbé V Index m Ri5=— 2.4012 61. 16 St=0.8238 to 0.0588 Ru= —0.4443 55 . D7=0.0847 Refractive Rri=+ 3.2245 0. 482 1. 5076 Thickness or Air Separation S5 =2. 0925 to 0.1493 0. 596 0. 531 Rn=+3.5000 R1a=+1.2695 50 0. 625 S4=0.1976 Rio= —0.6233 imum equivalent focal length F0 for Example III. Radius Sa=0.0847 Ra=+0.7554 The following table sets forth the numerical data for the rear member of Example IV in terms of the min 1. 404 1.307 S2=0.0l41 to 0.7791 Rs=+0.6995 suitable for use in the larger of such cameras. 1.612 Sr=+0.0014 Ra=+1.4870 above mentioned whilst the objective of FIGURE 4 is 1. 631 60 R|s=—- 3. 2562 1. 515' S1 =1. 8057 Rw=+ 3. 03956 2.070 D12=0. 2821 Ram 0. 342 w 1. 5151 56. 35 2. 063 Sa=0.7109 Rm= —10.3331 R11=+0.6348 R18='-1.2820 0. 547 D1u=0.0667 1. 6258 35. 74 D11=0.1555 1. 5097 64. 44 ‘ D12=0.1111 R2o= -= 1. 5151 ‘It should further be mentioned, however, that by con trast with the rear member of Example III, the rear mem 0. 696 Sr=0.7109 Rn=+1.1967 65 0‘ 815 56. 35 0. 812 In this example, the iris diaphragm B is located 0.044F0 in front of the front surface R13 of the rear member, ber of Example IV has only three components, two con vergent doublets in front of a simple convergent compo nent. It will thus be appreciated that the number and 70 arrangement of the components of the rear member may be considerably modi?ed, independently of the two axial ly movable members, according to circumstances. When correction for some or all secondary aberrations can be sacri?ced the rear member may be simpli?ed. Thus, in given position of adjustment remains unchanged. The 75 comparing the alternative rear members of FIGURES l, so that its position relative to the front members in any 3,045,546 16 15 2, 3 and 4, it may be mentioned that when a high degree of correction is required the slightly more simple design of FIGURE 4 is less satisfactory than the other designs, ?rstly because the rear member of FIGURE 4 has a small er collective power remote from the diaphragm so that the distortion produced by the front members cannot be as well counteracted as in the other rear members, and front member being greater than 1.5 times the equivalent focal length f1 of such front member. 3. An optical objective as claimed in claim 1 in which the convergent front member comprises a convergent doublet component and a simple convergent component located in front of such doublet component, the front sur face of such doublet component being convex to the front with radius of curvature between 0.5 and 1.0 times the secondly because the lesser number of surfaces remote equivalent focal length (h) of the convergent front mem from the diaphragm in the rear member of FIGURE 4 does not permit lateral chromatic aberration produced by 10 ber, at least one simple meniscus component in the di the front members to be as well counteracted as in the vergent second member having its rear surface convex to other rear members. the front with radius of curvature not less than 0.5f2 while the radius of curvature of the rear surface of the front component of the convergent front member is greater than It will, however, be clear that what , ever the arrangement of the rear member, such member should in each case alford aberration correction generally equal and opposite to the aberrations of the axially mov able members so that the complete objective is corrected with respect to the diaphragm. What I claim as my invention and desire to secure by Letters Patent is: ' 1. An optical objective of variable focal length cor- rected for spherical and chromatic aberrations, coma, astigmatism, ?eld curvature and distortion throughout 1.5 times the equivalent focal length f1 of such front member. ' 4. An optical objective as claimed in claim 1 in which the Petzval sum for all the surfaces of the stationary rear member lies between 0.7 and 1.4 times the positive value of the equivalent power of the divergent combina tion of the front two members in the position of adjust ment corresponding to the lower end of the range of rear member including at least six air-exposed surfaces and a divergent combination constituted by an axially variation of the equivalent focal length of the objective, such Petzval sum also lying between 0.35/f2 and 0.7/f2 and between 0.3 and 4.0, times the equivalent power of movable divergent member located in front of the station the rear member. the range of variation, comprising a stationary convergent ary rear member and an axially movable convergent mem ber located in front of such axially movable divergent member, the ratio of the equivalent focal length of the 5. An optical objective as claimed in claim 1 in which the Petzval sum for all surfaces included in the rear portion of such stationary rear member (that is the divergent combination of the front two members to the 30 portion having the rear four of the air-exposed surfaces equivalent focal length of the complete objective remain of such member) is positive and lies between 0.25 and ing constant and the virtual image of a distant object formed by such divergent combination having a constant axial position relative to the stationary rear member of the complete objective at the lower end of the range of variation thereof. 0.85 times the reciprocal of the equivalent focal length 6. An optical objective as claimed in claim 1 in which throughout the range of variation, and the convergent 35 the stationary rear member consists of two convergent front member comprisingla plurality of convergent com portions separated vby an air space whose axial length is ponents including at least one simple component and at greater than the equivalent focal length of either of such least one doublet component having a dispersive internal portions, while the ratio of the equivalent, focal length contact surface which is convex to the front, the differ ence between the refractive indices of the materials of 40 f3 of the stationary rear member to the equivalent focal length of the complete objective at the lower end of the the two elements of such doublet component of the front range of variation thereof lies vbetween 0.2 and 1.2 times member lying between 0.05 and 0.15, while the divergent second member comprises a plurality of divergent com ponents including a dirergent doublet rear component the f/ number of the objective. . 7. An optical objective as claimed in claim 1, in which having a collective internal contact surface which is con 45 at least one of the four rear air-exposed surfaces of the stationary rear member is ‘both collective and strongly vex to the front with radius of curvature lying between convex towards the diaphragm of the objective, whilst 0.665 and 1.573, where f; is the equivalent focal length the rear portion of the stationary rear member (that is of the second member, the mean refractive index of the the portion having the rear four of the air-exposed sur material of the rear element of such doublet component of the second member exceeding that of the material of 50 faces of such member) includes at least one internal contact between a convergent elementand a divergent the front element of such component by between 0.15 and element, the Abbe V number of the material of such 0.3, and the plurality of divergent components of the di convergent element exceeding that of such divergent ele vergent second member also including at least one di ment by at least 20. vergent simple meniscus component which has a rear sur 8. An optical objective as claimed in claim‘ 1, in which face convex to the front with radius of curvature not less 55 the diaphragm of the objective is located at or near the than 0.33 f2 and not greater than the range of axial move front surface of the stationary rear member, and the ment of such divergent second member, while the overall diameters of the front two members are made larger than axial length of the divergent second member lies between is necessary to accommodate the full axial beam, so that 0.6f2 and l.3f2, the ratio of the equivalent focal length of the relative aperture of the objective is determined solely 60 the divergent combination of the front two members to by the diaphragm and therefore remains constant the equivalent focal length of the whole objective lying throughout the range of variation. between 3 and 8 times the reciprocal of the f/ number of 9. An optical objective as claimed in claim 1 including the objective. a lens mount for housing the objective and means carried 2. An optical objective as claimed in claim 1 in which by the lens mount for axially moving the front member the convergent front member comprises a convergent independently of the second and third members to ef doublet component and a simple convergent component located behind such doublet component, the front sur face of such simple component being convex to the front with radius of curvature between 0.4)‘1 and 08h, where fl is the equivalent focal length of the convergent front member while the internal contact surface in such doublet component is convex to the front with radius of curvature between 0.4)‘; and 09h, the radius of curvature of the rear surface of the front component of the convergent fect focussing for near objects. 10. An optical objective as claimed in claim 1 includ ing a lens mount for housing the objective, and means carried vby the lens mount whereby alternative rear members can be selectively attached to the mount in the correct position relative to the front axially movable mem bers. 11. An optical objective of variable focal length cor rected for spherical and chromatic aberrations, coma, ' 7 3,045,546 17 18 astigmatism. ?eld curvature and distortion throughout the range of variation, comprising a stationary convergent tionary rear member lies between 0.3/f3 and 4.0/f3, where f;, is the equivalent focal length of such stationary rear rear member, and a divergent combination constituted by an axially movable divergent member located in front of member, the ratio of such equivalent focal length f3 to the equivalent focal length of the complete objective at the lower end of the range of variation thereof lying the stationary rear member and an axially movable con between 0.2 and 1.2 times the f/number of the objective. vergent member located in front of such axially movable 13. An optical objective as claimed in claim 11 in divergent member, the ratio of the equivalent focal length which the ratio of the equivalent focal length of the di of the divergent combination of the front two members vergent combination of the front two members to the to the equivalent focal length of the complete objective equivalent focal length of the whole objective lies be remaining constant and the virtual image of a distant object formed by such divergent combination having a 10 tween 3 and 8 times the reciprocal of the f/number of the objective while the overall axial length of the di constant axial position relative to the stationary rear vergent second member lies between 0.6f2 and 1.3f2. member throughout the range of variation, the convergent 14. An optical objective as claimed in claim 11, in front member comprising a convergent doublet corn which the equivalent focal length 1‘; of the convergent front ponent whose internal contact surface is dispersive and convex to the front with radius of curvature between 15 member lies between 1.0;‘2 and 1.67f2 times the value of the 0.4]‘1 and 0.9)‘1 and a simple convergent component expression (1+x/Q), Where Q is the ratio of the value of which is located behind such doublet component and the upper limit of the range of variation of the equiva has its front surface convex to the front with radius of lent focal length of the complete objective to the value curvature between 0.4)‘1 and 1.0f1, Where fl is the equiva of the lower limit thereof, the ratio of the equivalent lent focal length of the convergent front member, while 20 focal length of the complete objective at the lower end of the divergent second member comprises a divergent dou the range of variation thereof to the f/number of the blet component whose internal contact surface is col objective lying between 0.27f2 and 0.56f2. , lective and convex to the front with radius of curvature between 0.66f2 and 1.5]‘2 and at least one simple divergent meniscus component which is located in front of such 25 doublet component and has its rear surface convex to the front with radius of curvature not less than 0.33;‘2 and not greater than the range of axial movement of such divergent second member, where f2 is the equiva lent focal length of the divergent second member, the 30 stationary convergent rear member including at least six air-exposed surfaces, the Petzval sum for all surfaces included in the rear portion of such rear member (that is the portion having the rear four of the air-exposed surfaces of such member) being positive and lying be 35 References Cited in the ?le of this patent UNITED STATES PATENTS 2,165,341 2,649,025 2,741,155 2,746,350 2,843,016 2,844,996 2,847,907 2,937,572 tween 0.25 and 0.85 times the reciprocal of the equiva Capstaff et a1. ________ __ July Cook ______________ __ Aug. Hopkins ____________ __ Apr. Hopkins ____________ __ May Reiss ______________ __ July 11, 18, 10, 22, 15, Klemt ______________ __ July 29, Angenieux __________ __ Aug. 19, 1939 1953 1956 1956 1958 1958 1958 Yamaji ____________ __ May 24, 1960 FOREIGN PATENTS 7 lent focal length of the complete objective at the lower end of the range of variation thereof. 12. An optical objective as claimed in claim 11, in which the Petzval sum for all the surfaces of the sta 40 381,662 856,897 1,080,099 Great Britain _________ .._ Oct. 13, 1932 France ______________ __ Apr. 1, 1940 France ______________ __ May 26, 1954

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