Патент USA US2406807код для вставки
Sept? 3, 1946. _ p. |_. coLBATH 2,406,807 SIGHTING APPARATUS Filed :Dec. 17, 1945 4 Sheets-Sheet 1 42 lnventior-z Dan L.- Cnlbath, 1%. W76. ‘WM H is. Atbor'nes. Sept. '3, 1946. 2,406,807 D. 1.. COLBATH SIGHTING APPARATUS Filed Dec. 17, 1943 4 Sheets-Sheet 2 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ 4.m Dan by .O ‘L. Colba’oh, v en b F His Attof‘neg. Sept. 3, 1946.' ' p. 1.. coLBATH , 2,406,807 SIGHTING APPARATUS - Filved Dec; 17, 1943 * 4 Sheet's-Sheet 3 Ihven‘bor: “Dan Colbath, by :v' 62% His Abbot-“neg; Sept. 3,‘ 1946. ‘ D. 1.. COLBATH I 2,406,807 . SIGHTING APPARATUS Filed Dec. 17, 1943 4 Sheets-Sheét 4 - Inventor: ' Dan L..Co|bath, Hi Attorney Patented Sept. 3, 194-6 2,466,807 UNITED STAT-ES OFFICE. Dan L. Colbath, Schenectady, N. Y., assignor to; General Electric Company,‘ a corporation of New York ApplicationDecember 17, 1943, Serial No. 514,591. 5 Claims; 1. This invention relates. to sighting apparatus,‘ more particularly to sighting. apparatus which is especially useful. as. a. stadia range ?nder. Stadia range. ?nders operate on the principle that the range of a. distant. target whose actual (Cl. 88—2>.3~)‘ 2 In accordance with this invention, inv one em bodiment thereof}. there. is a setof'masking plates. including twoopaque plates-which have intersect ing- spiral light-conductingportions. The points of. intersection of‘ these spiral portions de?ne stadia. range ?gures in the form of spaced dots of lightarrangedin concentric circles, the diameters of which may be varied by rotating the plates rel ative to each other. One. plate. is rotated in ac the. observer an imageof a stadia ?gure the size 1O cordance. withlmcwn target. size, while. the. other. of which. may be adjusted,v to coincide with the i'srotafued in. accordance with target range so that; known dimension of the observed target. When when the proper. stadia circle coincides with the, coincidenceis obtained the size. of ‘the stadia?g target,_the target’ range is automatically deter ure bears a. ?xed relation to. the subtended angle mined. A. third opaque plate. is superimposed and target range,,.and‘ hence adjustable means for . upon the other two and. has a series of radial varying. the sizeoffthe stadia ?gure can. be cali light-conducting, portions. The. plates. are ar brated in terms. of. target range. ranged so that these radial ligntr-conducting por A stadiarange?nder is known whichcomprises tionspass thrcughbut one of. the series of points a transparent. member through which a target is of‘ intersection of the spiral light-conducting por observed. A collimating light-projecting system tionsof the other. two. plates that form. the proper is provided. which projects an image. of a stad'ia circular stadiarange ?gure, the remaining. points ?gure so that. it isre?ected from the transparent of intersection. of these. spiral light-conducting member into the observer’s line of sight where it portions beingmaskedout. This third plate. is al . appearsas a virtual image at an in?nite distance waysmovedthroughafraction of the angle of di and effectively coincident with. the observed tar 25 vergence. between the other two plates, as. they are get. Such an optical system is described and ' rotated‘. to vary the size of. the stadia. ?gure, so claimed in the .copending. applicationof Charles that itsradial' linesv always-pass through the points S. Grimshaw, Serial'No. 443,031, ?led May 15, of intersection of. thechosen stadla ?gure. 1942, and. which application. is assigned to the as For a. more complete understanding of this. in 30 vention, reference. should- be. had to the. accom signee of the present application. The Grimshaw systemv includes. a plurality of panyingdrawings in which Fig. 1 isavertical sec superimposed opaque. stadia. ?gure; generating tional'v View taken. through optical. sighting ap plates disposed between. thev sourceof light and paratus embodying thisinvention; Fig. 2 is a hori the re?ector and substantially in the focal’ plane zontal sectionalview taken through the appara of- the collimating system. These plates have a 35 tus shown. in Fig. 1;,Fig...3gis- a. front elevation of series of. light-conducting portions arranged to the apparatusshown in Figs. 1 and 2, parts being produce a. luminous. stadia ?gure. formed of a shown.v in section andpartsbroken away so as to plurality of points of lightappearing at the inter illustrate certaindetails of construction; Fig. 4 is sections of. the light-conducting portions of the an-end. elevationv illustrating parts. of the stadia plates. The light-conducting portions of the 40 ?gure generating apparatus.‘ used, in this invene plates have a con?guration such. that the points tion, parts being broken away and parts shown‘ size is known may be determined. by measurement of. theangle the target subtends at the eye ofthe observer.v The. subtended? angle is. usually meas uredby superimposingupon thev line of sight of of light are arranged in. av circle, the diameter of which may be varied by arelative rotative move. in‘ section so as- to illustratecertain details. of con struction, and.v the?gure. beingdrawn to a larger mentof the plates. ‘scale- than Figs. 1, 2,. and 3; Fig. 5 is a sectional A- plurality of sets of... cooperating masking 45 View taken: through the-line 5—5: of Fig. 4. and platesare provided which are calibrated to deter looking in. the:v direction of’ the‘ arrows; Fig. 6 is mine the ranges of differentsizedtargets; that is, an expanded‘ view illustrating: the-plates and an a di?erent set must be used. for each different associated member, this ?gure; being drawn to a sized target. _ ‘ larger scale than the preceding ?gures; Fig. 7 is This invention contemplates improvements in 50 an enlarged view showing the relationship of the the Grimshaw apparatus, including an arrange superimposedplates whenadjusted for maximum ment. wherein a single set of masking plates. can target range for agiven known minimum target be. used todeterminetheranges of targets. of any size;v Fig. 8 illustrates the. manner in which the‘ size. between the upper. and- lower limits of. target stadia ?gure gen‘erated‘by the plates shown in size. for which the. device is designed; 55 Fig. 7 appears to the observer; Fig; 9' is a View 2,406,807 3 similar to Fig. '7 except that the plates are ad justed for a shorter range; Fig. 10 is a view simi lar to Fig. 8 except that the stadia ?gure is shown adjusted for the shorter range when the plates are in their positions shown in Fig. 9 ; Fig. 11 is a view similar to Figs. '7 and 9 except that it illustrates how the stadia circle is increased for a larger 4 respectively attached thereto whereby they may be rotated. Meshing with the gear 33 is a pinion 35 mounted upon a shaft 36 which is journaled in the casing I‘! and which projects to the ex terior thereof, and which on its outer projecting end carries an adjustment knob 31. The gear 34 is driven by a pinion 38 which is mounted on a shaft as also journaled in the casing I]. This target size at the same range as in Fig. 9; Fig. 12 shaft is driven by means of a shaft 40 journaled is a view similar to Figs. 8 and 10 except that it corresponds to Fig. 11; and Figs. 13 and 14 are 10 in the casing l1 and positioned at right angles to the shaft 39, as shown. The shafts 39 and 49 diagrammatic views illustrating the principle of are interconnected by means of ‘bevel gears 4|. operation of the sighting apparatus. And the shaft 40 projects from the casing, as Referring to the drawings, there is illustrated shown, and on its outer end carries an adjust a stadia range ?nding apparatus arranged in ac ment knob 42., The ring 28 which supports the cordance with this invention and comprising a masking plate 22 is driven from the rings 26 and transparent re?ector Ill formed of glass or some 2'! through gears 43 and 44 formed on the two other suitable material through which a distant rings respectively and which mesh with a gear 45; target may be observed by an observer whose eye this gear 45 is mounted to rotate freely upon a is positioned at I I. The plane of the transparent shaft 45a which is attached to the ring 28, as re?ector Ill is disposed at an angle to the line of shown in Fig. 5. In the speci?c embodiment of sight I2 so that an image of a range ?nding stadia the invention illustrated, the gearing is such that ?gure projected along a line I3 to a collimating the ring 28 and hence the masking plate 22 always re?ector l4, positioned above the re?ector I0, and moves through one-half of the angle of diver from there back along this line 53 to the member I0 is re?ected from the surface of the re?ector 25 gence between the rings 26 and 21, and hence be tween the masking plates 2I and 23. Ill into the eye of the observer where it appears Mounted within the end plate 39 are a pair of as a virtual image superimposed upon'the line of sight I2. ‘ The reflector m is adjustably mounted upon av pair of brackets l5 supported by a‘ framework I8. This framework also supports the collimating re ?ector Ill, as shown. In addition, it supports a suitable light ?lter Ica pivotally mounted upon a bracket I?b for movement to a position in the light-collecting lenses 45b which function to col lect the light from the lamp I8 and to project it onto the masking plates. These lenses, as shown, are secured in the end plate 30 by means of a screw plug 450. The three opaque masking plates 2!, 22 and 23 are provided with series of light-conducting por line of sight I2, as shown in full lines in Fig. 1, tions, which portions in the embodiment of the to a position removed therefrom as indicated in dotted lines in this ?gure. invention illustrated in the drawings, are in the form of slots cut through the plates. The plate 2% is provided with a series of radially-arranged The unit including the re?ector IS, the colli spiral slots 66, the plate 22 with a series of straight mating reflector it, the frame l6 and the ?lter Ilia, is mounted upon a casing I‘l arranged at 40 radial slots Ill, and the plate 23 with a series of radially-arranged spiral slots 48 having the same right angles to the unit, as shown. Mounted shape as slots 46 but being conjugate to or re within the right-hand end of the casing IT, as versely arranged with reference to them. Each viewed in Figs. 1 and 2, is a source of light I8 plate has the same number of light-conducting which preferably will be an electric incandescent lamp; and at the other end of the casing there 45 slots in its series, and in each, corresponding slots are spaced alike; and moreover, the slots in the is a reflector IQ for directing the light rays from three series are positioned radially with reference the lamp up along the line I3 through the trans to circular slots 49, 58 and 5| provided in the parent reflector Ill to the collimating re?ector I6. three plates 2!, 22 and 23 respectively and located Interposed between the lamp l8 and the re?ec in their axis of rotation. . tor I9 is a stadia figure generating apparatus 26 In order to secure the desired degree of sensi which is arranged to generate the stadia ?gure tivity in adjustment of the diameter of a circle at the focal plane of the collimating re?ector l4 whereby the projected image thereof appears to formed by the intersecting points of the spiral the observer to be at an in?nite distance. This apparatus comprises a set of three opaque disks or masking plates 2I, 22 and 23, and an index plate 24, which members are shown more slots and also for the purpose of securing sharp intersecting points so that the light-conducting areas will be small and well de?ned, the slots 4t‘ and 58 have a relatively small radius of curvature; clearly in Figs. 5, 6, 7, 9 and 11. The assembly of these plates is mounted within a supporting ring 25 (Figs. 4 and 5). The plates 2! and 23 have a shallow pan-like shape and are mounted in the ends’ of the supporting ring members 26 and 2? respectively, while the third plate 221s also it is desirable to use a relatively large num ber of slots 66 and 48 so as to provide a circular stadia ?gure in which the dots are relatively close mounted in a ring member 28, all as shown more clearly in Fig. 5. The ring 26 isrmounted to rotate in an end plate 29; the ring 21 is mounted to rotate in the opposite end plate member 38; while the ring 28 is mounted to rotate on the rings 26 and 21. The index plate 24 is secured to the inner end of the end plate 30. . together. Because a largenumber of slots having a small radius of curvature are used, a given spiral slot 46 or 48 in one of the plates 2I or 23 will intersect a number of the spiral slots in the other plate at a number of points spaced at dif ferent radial distances from the axis 0 of the plates, ,as shown- in Figs. '7, 9 and 11. For exam ple, the slot 48a (Fig. 9) of the plate 23 intersects slots 46a, 46b, 48c and 46d of the plate 2| at the points A, B, C and D at radial distances OA, OB, OC and OD‘ from the central axis 0. The re ' The main supportingring 25 and the two end plates 29 and 39 are secured together as a unit maining spiral slots 48 of plate 23 intersect other and this unit is securedto an inturned flange 31 mounted in the casing H by means of screws 32. The rings 26 'and‘2‘l have spur gears 33 and 34' therefore neglecting the effect of the third plate 22, there would be formed in the observer’s ?eld spiral slots 46 of plate 2| in a similar way, and 2,4663%??? , s1; 6.. . of views dots lofi'li'ghtl fermingi a-tseri‘es of icon'c‘ener that} there I will be'fproj'ected into; the "line-20f P sight? tric iO'i'I‘01éS3aJ’0lH-1d':the centrall‘idot- of- light »'-wh'ichi* off‘theeob'server' ?gures whichl-indicatelthe target: si'ielmatchediiagainst' anlimage'o?lthe index‘ 53? all-"1 central 5openings»4-9,l--5?3 and 5115'” It will alsow-be? asishow-n inlFiéss8il9‘and 10} apparent‘that-asthe-pIatesZl- a-ndi 23 arerrotat’ed' relatively to each other these radii? wii-l'kontihu» ous-ly' change’; For example; the" circle-of; dots with'aadi'u'sOC' of-lF‘igi 9;7 which" forms the ‘stadila ?gure sli0w~1rin~Fig1 1'0; wi1l~be reduced’ in ‘diam-f etier t0 gene-rate'ethestadial-circleshown in Fig‘. 8'3 having5 a*\radius-OG"‘b'y4 moving the plates-from their-positi'onsof-Fig: 9' tol'tHeir positions of? Ffge ‘75' Iri- order to-avoid possibleecon-fusion offth'e'obe' ‘ ‘ " The‘ theory orop'eration: maybe ' better under: ‘ stood by referencetb-Fi'gsa Band ‘14:1 The stadiai ringlof ‘dots'iB (Fig.‘13)‘, which"spans’theiouterztipsf of the target, has radius p. The knownwihgspan isD, ' Therefore: ' v server ‘as to which ~ circle ism vbe ‘used! fer <stadia measurement it: is desired-that? all! ‘but the-“properv 15' oneeofith'e ‘series-of? concentric" circles "be masked onty‘lthap‘l-ate 2-2 does-this: Itiwill bB‘ObSGI‘VGd‘bYi reference‘td?g: 9 that theeradial‘slot/41d- of~plate 27211'pas‘ses ‘through - the ~peint'1of'l‘interse-cti'orr G"of~'= spiral bIOtslBdar-rdl?c, andithat likewise uitslco "-e 205 panionate radial - slots- pass through? the‘ other’ points! of? intersection of» ‘the spiral I lines <46"»and£ 41? vlwhich-l de?nei the) stadi'a; circle‘ ofiFiga 10,7 but ' thatlall? other-points =01’ 7intersection between; the New referringytoiFig.‘ 1-4; theisl-otsrd'?ii4?-'anduMi: slotsll?» andfd'giwil-l be masked out‘; tthu-s, the-'pointsi intersect zat=point R which lies in afcircleeofrradiusr p; .Aszthe curvature of the slots ' Miranda 48 are: equaLrthe point of'intersection P“Wi'11:00C1l1’.:ail'0ng: an'd'the slots-45a; 45b and‘ 'li’?dwilPbe-mask‘ed "out; a line ‘bisecting-_;tlrretv angle ‘¢r¢}:~¢z<which,makesithe angle (91:02‘v (the:~line:O'—X¢ being: an arbitrary‘ ' When-thap-lateg 2|?v and; 23* areangularlyradi 30' reference dine) .‘ Asaslotr?‘ofe diskx22~ always .bi sectssthe. angle zqir?imewhich ~isr the: angle :of sch-= justedwith relation to‘ each other, say‘ byr‘rotating‘ vergence betweenvdisks?2:’andr23athem ' . pIateIZJI‘ counterclockwise from its position of Fig.‘ 9'1 to<~its ‘position of .‘Fi’g. »'7,'v the'rpl‘ate '- 22~by>~¢vilrtue and-‘so also will all other-unwanted points-of»? in; tersection. ~ ' > ~ ~ ' ' of'thefact- that "it moves-through-lone-half the angle of divergence between the p1ates-2-1-1andT233 willé'move-its-radial line ‘4 Ta to always pass-through tlie~point of intersection (T, C’f betwee-n‘ithe-E spiral. slots 48w and546'c1; and again-all- the points ofiinv-a tersection between thespiral-slots-ll? and¥48iiwill be‘- masked’ out‘ except‘ those; lying; in» the‘ circle 40 wh'oseeradius is/OC". In this way; only-loneicircle: ofi dots:v appears in. the observers a?eld‘ of iview-and its-diameter‘ may be varied byrotating the?twov plates iii-land 23 -re1atively~1to=each otheri: Thearrangement of plates-'shown'in Fig. 11 corr‘-' 45 responds-tea settingv forv a-‘larger targetsize; the‘ dimensions of" this target being"v twice that: satin _ Figs. 7'"- and-I91 It infill-be‘ observed that*infFig.'.11I. the slots ABIinterseCtthe slots Ab'iand 41 at points‘ lrin‘gwon a circle whoselradiusisiOC”. - » ‘As pointed outab'ove; in-the;em-bodimentiof-the invention-1. illustrated ' in the drawings;: the spiral? slets Miami; 48 have'lidénticallyitlie-same curva-'-» ture‘.‘ Moreover, ‘ they: are; logarithmic-‘spirals; The-‘plate 23'ih‘av-ing-1 the lSlOts' 48i isvv adiustedi'byl knob‘ 42 in accordance‘witli the ~logarithm1range ; while ‘the? plate -2 'I having slots 46 adjusted.‘ by knob' 3T-liin ‘accordance? with the’ logarithm" of.itar‘get ‘size. ‘ T6 assist the nb‘server in making. the; 1at= t'erv‘adju'stment, the plate'ilwis calibrated in terms‘ of- target size in feet,» for example',:1wing' span-in feet,. andlis providedlwith scale slots‘i 52ito indie cateetheecalibration; Th'e?sc'ale. 52 'is' matched? against a: ?i'z‘ed reference-index 53iin1the form ‘of aj~triangular slot'formed 'inithe» ?xed p'lateil?; The '- plate1~24i is providedwith raI-?'ange: 54 which masks" out-the major portion 10f fthe scale .52; only theiindi'cia-I-of -' this scale.‘ adj acent~the index; 5'3 being‘ exposed; this ‘range = of‘. the; scaleis exposed byla-n‘otch‘ 55 fer-med in the ?ange-54; This-notch? 55'v aligns with elongatedislotsr'56- an'd'iST for-med; in the plates 22‘and-l2'3 respectively, a'n'd'Lthe plate‘ 2| isprovided With an elongated slot 58 which is alignedlwith the ?xed‘index 53. > ‘ which isthe desired relationship. 50 to log’of" rOtatedJanamOunt equal ‘ e‘ V lf D and‘ disli 23* is.rotatedfuntifpoints, P'occur atla radius p which spans the target,._then rotatibn of‘ disk 23 is equal'to the log,K'1R;.. In. using this apparatus,- the observer ?rst‘de termines by recognition‘of the target'tlie proper‘ set'of the plate "2 I“ to be used in the rangedet-er min'ati'on; this;( as pointedfout previouslxg. isef fected‘b'y; setting the knob 31.. The observer then viewsthe target through the transparent; member. l0 and. sees re?ected in the line of ‘sight an‘image of a" luminous stadi’a‘ ?gure-compris ingriaiplura'lity of vvpoints arranged in the. form of‘ .a .circle and a'luminousdotat the center of vthe circle,_ as pointed out‘ above. This observed imageapp'ears to be at an in?nite distance. and‘ sincei-t is superimposed upon the ‘line of .sight by the. re?ector I4 on’ the. transparent member l0;;it appears effectively coincidentlwithithe tar. get'.. Thediameter of‘thi's circle may. be varied by'rrotiatingithe knobv 42 which rotatestherange plate2’3‘." The knob‘ 42"‘is' adjustedby 'tlie’obi' , In view of the foregoing, it will’ be understood 75 server until two diametrically opposite points of 2,406,807’ 7 the stadia circle are superimposed upon the out ermost extremities'of a dimension of the target, such as the wing span of the aircraft shown in Figs. 8, 10 and 12. This movement'of the range 8 a luminous stadia ?gure comprising a plurality of points‘of, light arranged in a circle is produced at the intersections of the light conducting por tions of said plates, the diameter of said stadia plate automatically determines the range of the ?gure being variable by a relative rotation of said target, and its movement may be utilized in aux ?rst two plates. . ' 3. In an optical sighting device, a transparent iliary equipment indicated by ‘the numeral 59 member through which a target may be observed, driven by the shaft 39. a light projecting system for producing a virtual While in the speci?c embodiment of, the in vention illustrated in the drawings, the spiral 10 image of a variable sized stadia ?gure in the lines 46 and 48 of the two plates 2| and 23 have the same curvature, they may have different curvatures. In case they do, the masking plate 22 would not be driven at half the speeds of the line of sight of the observer by re?ecting an image of said ?gureon said member, said system comprising a source of light, a collimator, a pair of superimposed opaque masking plates disposed plates 2| and 23, but it would be geared to them, 15 between said source of light and said transparent member and located in approximately-the focal so as to be driven at some multiple which would be satisfactory tocause its radial light-conduct ing portions always to pass through the proper points of intersection of the light-conducting 20 portions 46 and 48 of the other plates. While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to \be limited‘ thereto since many modi?cations may be made, and I there fore contemplate by the appended claims to cover any such modi?cations as fall within the true spirit and scope of my invention. What I claim as new and desire to secure Letters Patent of the United States is: plane of- said collimator, said masking plates having series of logarithmic light-conducting curves which are conjugate in pairs and intersect each other at a plurality of points arranged in concentric circles, means forrotating one of said plates in accordance with the logarithm of the known dimensions of said target, means for rotat ing the other in accordance with the logarithm of the ‘target range, a third superimposed opaque plate having a series of radially extending light conducting portions which intersect the curved light-conducting portions of said ?rst two plates through their points of intersection in, a prede 1. In an optical sighting device, a transparent 30 termined one only of said concentric circles, the remainder of said circles being masked out by member through which a target may be observed, by said third plate, and means for driving said third a light-projecting system for producing a virtual plate so that its said radial portions always bi image of a Variable sized stadia ?gure in the line sect the angle of divergence between said ?rst of sight of the observer by reflecting an image of said ?gure on said member, said system compris 35 4.; stadia-generating apparatus comprising a ing a source of light, a collimator, a pair of pair of superimposed opaque plates, one of said superimposed opaque masking plates disposed plates being provided with a series of spaced between said source of light and said transparent two'plates. _ i I logarithmic curved‘ light-conducting portions member and located in approximately the focal _ plane of said collimator, said masking plates 40 that are calibrated to known target size, and the having a series of light-conducting portions ar ranged to intersect and thereby produce a lumi nous stadia ?gure, the proportions of which may be varied by relative movement of said masking plates, means for rotating one of said plates in accordance with the known dimensions of said target, and means for, rotating the other of said plates to vary said proportions of said stadia ?gure to cause said stadia ?gure to coincide with said target and thereby determine the range of . said target. I 2. In an optical sighting device, a transparent member through which a ‘target may be observed, a‘ light-projecting system for producing a. virtual image of a variable sized stadia ?gure in‘ the line of sight of the observer by re?ecting an image,‘ of said ?gure on said member, said system com prising ‘a source of light, a collimator, a pair of other plate being provided with an equal number of ‘spacedlogarithmic curved portions that are calibrated to ‘target range, the latter portions being conjugate in pairs with the ?rst-named series of light-conducting portions and intersect ing, them so as to produce a series of light-con ducting points, and means for setting said one. plate'in accordance with known target size and the other in accordance with target range. 5. stadia-generating apparatus comprising three superimposed opaque plates, two of said plates having series of identicallyeshaped‘ loga rithmic spiral light-conducting portions ar ranged conjugate in pairs so that they intersect at a' plurality of series of spaced points arranged in concentric circles, means for rotating one of said two plates in accordance with the logarithm of known target size and the other plate in ac cordance with the logarithm of target range in superimposed opaque masking plates disposed between said source of light and said transparent 60 order to‘ vary the diameters of said circles, the third of, said plates being provided with straight member and located in approximately the focal radial - light-conducting‘ portions that pass plane of said collimator, said masking plates hav through the points of intersection of said spiral. ing series of spaced curved light-conducting por- . light-conducting portions that lie in a prede tions, respectively, which ‘are conjugate in pairs, termined one of said ‘concentric circles, and a third superimposed opaque plate having a series of radially-extending light-conducting ‘portions, means for independently rotating each of said ?rst two plates, ‘and means 'for rotatingv said third plate responsively to rotation of either of said ?rst two plates so that the third plate always takes the same predetermined angular, relation ship to the other two plates, irrespective‘ of ‘the angular divergence between them, said. various light-conducting portions being arranged so that means for operating said third plate through one-half the angle of divergence between said two plates so that said radial portions always pass through said lines of intersection, of said prede termined circle, irrespective of the adjustments of said two'plates, the remainder of said circles being‘m-asked out by said third plate. , DAN L, ,COLBA'I'H.