Патент USA US2388609код для вставки
_ Nov. 6, 1945. A. 1. ERICSSON 2,388,609 AUTOMATIC CAMERA~DIAPHRAGM ADJUSTER Filed May 17, 1943 My Patented Nov. 6, 1945 2,388,609 UNITED STATES PATENT OFFICE 2,388,60Sl AUTOMATIC CAMERA-DIAPHRAGMZ ‘ ADJUSTER Arvid I. Ericsson, Chicago, Ill.‘ Application May 17, 1943, Serial No. ‘487,257 7 Claims. (CI. 95-64) My invention relates to automatic camera adjuster includes a photoelectric vcell, which is diaphragm adjusters. That is, it relates to mech mounted to be in?uenced by the same light con anism for automatically varying the size of the , iris diaphragm opening of a camera in accord ance with variations in light intensity so that substantial uniformity of exposure may be se the photoelectric cell in accordance with changes in the intensity of light acting upon the cell, step cured. by-step mechanism for selectively actuating the Although applicable to so-called. "still picture” ditions as the camera lens or ?lm, a relay, pref erably of the galvanometer type, controlled by diaphragm so that its opening may be contracted cameras, the invention is likely to have its great- or expanded as conditions require, and relays and est utility in conjunction with moving picture 10 electrical circuits whereby the response of the cameras, since in the operation of the latter, the necessity for or desirability of continuity during galvanometer to the varying intensity of light example, during the "taking” of a parade in the also be provided a manual adjustment whereby the range of automatic expansion and contrac tion of the diaphragm opening may be shifted to accommodate the automatic movements of the acting upon the photoelectric cell causes the step the ?lming of some particular scene or occurrence by-step mechanism to operate in one direction may render impossible manual diaphragm ad or the other, depending upon whether the light justment for change of light intensity. Thus, for 15 diminishes or increases in intensity. There may open air, the passage of clouds across the sun, resulting in greater or lesser and possibly fre quent increases and decreases in light intensity, or desirable movement of- the camera, which may 20 diaphragm to different general conditions, such result in shifting of background from light to as the previously mentioned differences in film dark objects and vice versa, makes one dia emulsion speeds, etc. phragm “setting" incapable of producing uni . Referring now to the drawing, the size of the form exposure; and of course, continuity is lost iris or light opening of the camera may be if the “taking” is interrupted in order to per 25 changed and governed by‘, the usual diaphragm mit manual adjustment of the iris opening. leaves 5 and-an actuating ring 6. In a manner The principal object of my invention is to well known in the art, and consequently which provide a reliable automatic adjustment of dia needs no illustration or explanation, the clock phragm so that the iris opening is expanded and wise and counterclockwise rotation of ring 8 ef contracted as the light intensity decreases and 30 fects movements of the diaphragm leaves to con increases. tract or enlarge the central lens or iris opening Another object is to provide an automatic ad de?ned by them. Diaphragm ring 6 is provided juster which can be easily and quickly adapted with a gear sector l’, the teeth of which mesh with to different ranges of diaphragm opening so as the teeth of a pinion 8 so that rotation of the to accommodate itself to different conditions of 35 pinion in one direction or the other causes the operation, such as different ?lm-emulsion speeds, diaphragm ring to move correspondingly, either shifting between color and black and white pic to enlarge or to contract the iris opening in the tures, and differences in general or overall envi ordinary manner. The shaft of pinion 8 has a ronment, such for example as the marked con ratchet wheel 9 rigidly secured thereto. This trast between taking a picture in dense woods 40 ratchet wheel 9 may be engaged and rotated step and of a snow scene on a generally sunny day. by-step either clockwise or counterclockwise by Another object is to provide automatic ad pawls I0 and II, respectively. Pawls l0 and H justment mechanism which, although controlled are pivotally carried on bell crank armature le by a photoelectric cell, derives the power for op vers l2 and I3, respectively, which are mounted 45 upon ?xed pivots l4 and I5, and acted upon by erating the diaphragm from a diiferent source. A further object is to provide mechanism in electromagnets l6 and II, respectively. A pin corporating elements of currently available [8, against which a tension spring l9 biases pawl equipment, such as commercial photoelectric l0, guides the movements of pawl l0; and in cells, ordinary ?ashlight batteries and relays. like manner a pin 20 against which a tensioning Other objects and advantages will hereinafter 50 spring 2| biases pawl l I guides the movements appear. of pawl H. Compression springs 22 and 23 bias The accompanying drawing shows, more or armature levers I2 and I3, respectively, against less diagrammatically, a typical embodiment of the attraction of their respective electromagnets. my invention. When the electromagnets are deenergized, the In general, the preferred embodiment of my 55 springs 22 and 23 retract the armature levers 2 3,888,609 against a stop 25, and in this condition the guide pins I3 and 23 insure that both pawls are dis engaged irom ratchet wheel 9 as shown in the drawing. However, when either electromagnet is energized, its armature lever and pawl causes the ratchetwheel to move a step in a correspond tact 15 or 11 to interrupt whatever circuit might otherwise be completed therebetween. I have found that suilicient power to energize the power magnets and actuate the diaphragm of an ordi- . nary amateur moving picture camera may be ing direction. Thus, when electromagnet I6 is had from two commercial ?ashlight batteries. The two spaced galvanometer contacts 33 and energized, it rotates armature lever I2 in a clock 31 are carried upon one arm of a bell crank lever wise direction about its pivot I4, causing pawl III 33, which is mounted on a ?xed pivot 3|. The to engage a tooth of ratchet wheel 9 and rotate 10 other arm of lever 30 has a projection 32 bearing the ratchet wheel and pinion 3 one step in a upon the peripheral surface of a cam disc 33 clockwise direction. And when electromagnet I1 which is frictionally retained upon the cylindrical is energized, the reverse action takes place, viz., ?ange 34 of diaphragm ring 3 by suitable means, armature lever I3 is rocked counterclockwise and such as a pipe clamp 33. As shown, a sector of ratchet wheel 9 is moved one step in a counter 16 cam disc 33 is provided with an eccentric cam clockwise direction. surface 36 which gradually inclines away from The energization of electromagnets I6 and I1 the axis so that as the cam disc move’; counter is governed by the action of light upon a photo clockwise. bell-crank 33 is rocked counterclockwise electric cell 30 which is mounted adjacent the about its pivot 3|, and vice versa. Thus depend iris opening or lens of the camera in such a posi nt upon the inclination of cam 33 and the location 20 tion that it is pointed in the same direction and of projection 32 thereupon, changes may be made in?uenced by the same light conditions as the in the angular position of bell crank lever 33 camera lens. I have found that a Weston Pho with a resultant change in the relation of the two tronic (Central Scienti?c Co. No. 80915) cell, galvanometer contacts "-31 with respect to the which transforms light directly into electrical movements of needle contact 35. A biasing spring _ energy, gives satisfactory results. The terminals 25 31 insures that projection 32 always bears ?rmly of photoelectric cell 30 are connected by wires 3| upon cam surface 33 so that the bell crank lever and 32 to the opposite terminals of the movable rocks clockwise or counterclockwise as the cam armature coil 33 of a sensitive galvanometer re disc moves one way or the other, as will be pres- ’ lay 34. For this purpose, I have successfully ently explained, in response to changes in light used a Weston model 334 DC (Central Scienti?c 30 intensity. Co. No. 80920) ‘galvanometer. The galvanometer A worm 95 formed as a part oi’ adjusting stem armature 33 carries a needle 35 which is posi 96 is journaled in a bracket 31 carried by dia tioned between two ?xed contacts 36 and 31 and phragm ring 6 and meshes with a gear segment 33 directionally biased by a small hair spring (not formed in the periphery oi’ cam disc 33. Rotation shown) toward contact 36. The voltage gen of stem 96 enables relative movements in both erated by the action of light on cell 33 is directly clockwise and counterclockwise directions be proportional to the intensity of the light and the tween diaphragm ring 5 and cam disc 33. If de de?ection of the armature of galvanometer 34 sired, vdiaphragm ring 3 may be provided with a is directly proportional to the voltage impressed 40 pointer I33 movable over a scale calibrated to thereon by cell 30. 'The spacing of contacts 33 the various iris openings, e. g., “F stops”; and like and 31 is ?xed, but they are mounted so that wise cam disc 33 may be equipped with a pointer their relation to the movable contact or needle 35 IUI movable over a scale indicative, for example, may be changed in a manner 'and for a purpose to of emulsion speeds of ?lms. The adjusting stem be later explained. 96 may, as desired, be located either inside the The ?xed contacts 36 and 31 of galvanometer 45 camera casing or outside of it, depending upon 34 are connected by wires 45—46 and 41-43 re whether it‘ is considered preferable to have the spectively to one terminal of the winding of re adjustment more or less accessible. lays 49 and 53; the other terminals of the wind In order to prevent inductive discharges, which ings of these relays are connected by wires 5i 50 may be caused by the opening of the circuits of 52-53 and 54-—55—53, respectively, to one side electromagnets 43 and 53, creating objectionable of a battery 60. The other side of battery 60 is sparking at the galvanometer contacts, the coils connected through a switch 6i and wires 62—63 of these magnets may be bridged by small con to the movable-needle contact 35 of galvanometer densers I33 and I34. respectively. 34. Thus, with switch 6| closed, the movement 56 Switch iii, the closing of which initiates the of needle 35 into engagement with contact 36 en operation of the automatic iris-opening adjuster, ergizes relay 49 over the circuit 63—6 I —62-63 is preferably of the push button type. It may, as 35-36-45-46-49-5l-52-53 back to bat desired, be associated with the button which con tery 63. And when the needle 35 engages con trols the feeding of the ?lm and the action of tact 31, the relay 50 is energized over the cir the camera shutter so that both the camera and cuit 60-6I-62_63-35—31-41—43-5Il-54the adjuster start functioning at the same time; 55-53 back to battery 60. or this button may be independent of the camera Upon energization, relay 49 closes its contacts control. 10-1I to complete a circuit for electromagnet I6 The operation will now be reviewed. If, upon over the path from battery 63 through switch GI 65 the closing of switch 3 I, the effect of the light upon and over the path 64-1I--'|0—12, the coil of cell 30 is such that the voltage generated thereby magnet l6, conductor 13, the contacts 14-15 of is su?lcient to enable the galvanometer arma magnet I3, wire 16 which interconnects contacts ture to overcome the force exerted by its biasing 15 and 11 of magnets I6 and I1 respectively, and. spring so as to move the needle 35 out of engage wires 19-55-53 back to the battery. Contacts 70 ment with the contact 33, but insu?lcient to en 14 and 18 are related to the armatures of electro a'ble the armature to move the needle into en magnets I6 and I1, respectively, in such a way gagement with contact 31, no energizing circuit that when either electromagnet is energized, the _ will be completed and the apparatus will remain armature l‘ever thereof causes the associated con inactive. Under such conditions, the iris opening tact 14 or 18 to separate from companion con 75 is proper for the intensity of light existent. .. 2,388,609 3 Assuming now that the light intensity for some reason diminishes, for example, a cloud obscures until the action of cam 66 is such that contact the sun or the camera is moved to point toward a which the galvanometer biasing spring can move needle 35 against the counter armature turning darker background. The diminished intensity ‘of light causes the photoelectric cell to generate a lower voltage with the result that the hair’ spring acting upon' armature 33 rotates it to swing needle 35 against contact 36. As soon as needle 36 en gages contact 36, a circuit is completed for relay 36 has been moved beyond the range through force of the voltage generated by cell 30 under a particular light intensity. Thereupon the sep aration of needle 35 and contact 36 opens the en ergizing circuit for relay 49 and the step-by step_ diaphragm-opening movements cease be 46 from battery 60, switch 6|, conductors 62-63, 10 cause the opening corresponds to the existent light needle 35, contact 36, conductors 45-46, the coil intensity. of relay 49, and the conductors 5l-52 and 53 back Ii’, on the other hand, the light intensity at to the battery. Relay 6! is thereupon energized any time increases, the higher voltage generated and its contacts ‘Hi-1| close. The closure of by photoelectric cell 38 causes the galvanometer these contacts completes a power circuit for actu 15 needle 35 to engage contact 31. The engagement ating magnet l6 over a circuit from the battery of contacts 35-31 completes a circuit through through switch 6|, conductor 64, contacts ‘II-10, relay 50 over the circuit from battery 60, switch conductor ‘I2, the coil of magnet l6, conductor ‘I3, 6|, conductor .62-63, needle 35, contact3‘l, con contacts ‘ll-‘l5, conductors 16-19-55 and 53 ductors 41-46, the winding of relay 50 and con back to the battery. The resultant energization 20 ductors 54-55-53 back to the battery, with the of magnet l6 performs two functions in sequence. result that its contacts Nil-I05 are closed. The First, it causes its armature lever i2 and pawl ID closing of relay contacts Ind-I05 completes a cir to advance and rotate ratchet wheel 6 one clock cult through power magnet I‘! over the path from wise step. This clockwise advance of ratchet battery through switch 6|, conductor 62, relay wheel 9 causes pinion 8 and gear sector ‘I to 25 contacts IDS-I84, conductor I06, the winding of rotate diaphragm ring 6 through 3. correspond magnet ll, conductor I01, magnet contacts ing arc in a counterclockwise direction, which 18-", and conductors 16-19-55-53 back to opens the diaphragm a corresponding amount to the battery.‘ The energization of power magnet let more light go through the camera lens. Sec i1 produces two effects in sequence, just as has ond, it causes contacts 14-15 to separate to 30 been described in connection with magnet l6. interrupt the circuit through magnet 16 even First, it causes pawl H to rotate ratchet wheel 9 though the contacts 35-36 at the galvanometer in a counterclockwise direction; and second, it remain together and as a result relay 49 remains effects the separation of its contacts ‘ll-18. The energized. Thus, the magnet l6 effects its own de rotation of ratchet wheel 9 in a counterclockwise energization after it has caused the ratchet wheel 3. direction causes pinion 8 and gear segment ‘I to to advance a step, whereby its pawl I0 is retracted rotate diaphragm ring 6 and cam disc 83 through preparatory to producing another step, and con a small arc in a clockwise direction. This move tinuance of step-by-step operation is insured until ment of the diaphragm ring closes the iris open the proper diaphragm adjustment is made. In ing a corresponding amount and the movement addition to the increment opening of the dia 40 of cam disc 83 causes a lower part of cam surface phragm, the step of counterclockwise movement 86 to be presented in contact with projection of the diaphragm ring 6 also causes cam disc 83 82. Therefore, biasing spring 81 moves bell crank to move counterclockwise through a small arc lever 60 to the right or in a clockwise direction, with the result that projection 82 of bell crank which tends to move contact 31 beyond the range lever 80 contacts a higher portion of cam surface 45 of the deflection of needle 35 caused by the volt 86. The result is that bell crank lever 80 is rocked age generated in cell 30 under the particular light slightly in a counterclockwise direction to move intensity then existent. Such increment closing contact 36 slightly in the same direction as the of the diaphragm opening continues until the re galvanometer spring is tending to move the arma lation of cam 86 and projection 82 are such that ture and needle 35-i. e., to the left. And if this 50 contact 31 has been moved beyond the range movement of contact 36 is sufficient to separate it from needle 35, no further operation ensues, be cause the diaphragm has been opened by the one step an amount su?lcient to compensate for the decrease inlight intnsity. However, if the light intensity affecting cell 36 is so low that the voltage generated therein is insu?lcient to balance the action of the coil spring acting upon the arma through which the photoelectric cell voltage cre ated by the present light intensity can swing needle 35, whereupon movement ceases, because the diaphragm opening then corresponds to the light intensity acting upon the photoelectric cell. Thus, during the “taking” of a picture, the dia phragm opening will expand and contract auto~ matically in accord with variations in light in ture. and as a result needle 35 is swung to the just as long as control switch 6! remains left further than the ?rst step movement of cam 60 tensity closed. surface 86 has moved contact 36 in the same direc Under some conditions, it may be desirable that tion, then the engagement of needle 35 and con tact 36 persists and relay 49 remains energized the range of the expanding and contracting of the diaphragm opening be shifted. In other with its contacts ‘HI-‘II closed. Then, as soon as spring 22 of power magnet I6 has retracted 65 words that, for example, the minimum opening and also the maximum opening to which the auto armature lever l 2 so that pawl ID has disengaged matic adjuster can move the diaphragm leaves ratchet wheel 9 and contacts 14-15 are again be reduced in size. Such a change may be ad engaged, the energizing circuit for magnet 16 is visable to secure the best results if extremely high re-established and thereby another step of dia speed ?lm is substituted for much less sensitive phragm opening is produced and cam 86 presents ?lm. Or if, for example, color ?lm is substituted a still higher level to projection 82-the latter for the more rapid black and white ?lm, a shift condition resulting in contact 36 being moved an in the opposite direction may be desirable to pro~ additional small increment to the left. Such duce the most satisfactory pictures from an ex step-by-step movements continue-the dia posure standpoint. The desirable shift in the phragm opening being enlarged more and more 75 range of iris operation may be brought about by 2,888,609 4 . altering the relative positions of diaphragm ring circuit individual to and closable by each relay; 6 and cam disc 83. Such alterations of relative. an electromagnet in each power circuit; and dia phragm actuating mechanism operable in one direction by one electromagnet and in the oppo position are e?ected by turning the adjusting stem 86 in one direction or the other, depending upon whether the shift is to be toward smaller site direction by the other electromagnet, said or larger diaphragm openings at opposite ends diaphragm actuating mechanism including cam of the automatic expansion and contraction. means to actuate the contact mounting means to of ggirse, similar results may be obtained by move the pair of galvanometer contacts in the the use or appropriate ?lters in lieu of such a same direction as the de?ection of the galvanom 10 eter armature. mechanical shift 01' range. By the use of sensitive low power relays in the 3. In a camera having the usual adjustable galvanometer circuits to control heavier duty diaphragm to provide exposure openings of dif magnets deriving power from batteries?such as ierent sizes, the combination of step-by-step ordinary ?ashlight batteries-it is unnecessary mechanism for expanding and contracting the to depend upon the photoelectric cell- to deliver 15 diaphragm opening, a photoelectric cell respon more than very small currents. This is a matter sive to the light conditions to which the camera of importance with present day photoelectric cells lens is subject, a galvanometer connected to the of the voltage generating type because, as far as cell so that the armature moves in accord with I am aware, they are incapable of delivering much voltage changes created in the cell by light in power-enough satisfactorily to operate the usual 20 tensity changes, 'a contact carried by the gal camera-diaphragm mechanism. A further ad vanometer armature, a pair of spaced contacts, vantage ?ows from the interposition of extrane one on each side of the armature contact and ously powered mechanism-especially step-by selectively engageable thereby depending upon step mechanism—between the photoelectric cell whether the light intensity acting on the cell in control and the diaphragm, via, a lessening of 25 creases or decreases, means mounting the pair of‘ the tendency for constant variation in iris open spaced contacts, means movable with the camera ing which might result in more or less fogging diaphragm and by the step-by-step mechanism of the negatives. Thus, although the apparatus may be su?iciently sensitive to produce substan for moving the contact mounting means in oppo site directions, a relay connected to each of the tially uniform exposure, it is not so supersensitive 30 spaced contacts, both being connected to the as to be affected by light variations which are armature ‘contact so that one or the other relay is of no consequence as far as ?lm exposure is con energized depending upon-Which of the spaced cerned. contacts is engaged by the armature contact, a ' The automattic adjuster mechanism which I pair of operating electromagnets operatively as have herein speci?cally described, lends itself 35 socaited with the step-by-step mechanism so as readily to construction as an attachment for dia to operate the same in opposite directions, and phragm control of present day standard cameras, a circuit between each relay and one of the op or it may be built in‘ as an integral part of a special camera. erating electromagnets closable by the energize. Letters Patent is as in?ows: the diaphragm opening when moved in opposite tion of the corresponding relay, and a source of Having illustrated and explained the nature 4;) electrical power for said circuits. and a typical embodiment of my invention, what 4. An automatic camera-diaphragm adjuster I claim and desire to secure by United States including a ratchet which expands or contracts , - 1. In a camera having the usual adjustable directions; a pair of electromagnets, each oper diaphragm to provide exposure openings of dif 45 ating a pawl which moves the ratchet in one of ferent sizes, the combination of a photoelectric its two directions of movement: a pair of relays, cell responsive to the light conditions to which each having contacts for closing a circuit for one the camera lens is subject, a galvanometer con of the electromagnets; a galvanometer having an nected to the cell so as to de?ect in accord with armature carrying a movable contact, and two variations of voltage generated by the cell under 50 relatively ?xed contacts, one engageable by the _ varying light intensities, step-by-step mechanism movable contact upon de?ection of the armature in opposite directions to close a circuit for one or for actuating the camera diaphragm, said mech~ anism being responsive to de?ections of the gal vanometer, a source of power for actuating the step-by-step mechanism, cam means movable 65 \ with the camera diaphragm, and means actu direction of armature de?ection; a photoelectric cell subject to the same light conditions as the ated by the cam means to cut off the source of the galvanometer so as to effect de?ections there power from the step-by-step mechanism when the diaphragm opening is proper for the existing of in accord with changes in light intensity; a mounting for the two relatively ?xed contacts movable to shift the contacts in either direction relative to the armature contact; and means op eratively connected with the contact mounting light conditions. 2. In a camera having the usual adjustable dia phragm to provide exposure openings of different sizes, the combination of a photoelectric cell re sponsive to light conditions to which the camera lens is subject; a galvanometer having its arma ture'connected to the cell so as to de?ect in ac cord with variations in voltage induced by light to 65 the other of the two relays depending upon the camera lens and connected to the armature of and with the ratchet to move the mounting in one direction or the other so as to alter the relation between the ?xed and movable contacts of the galvanometer. 5. In a camera having the usual adjustable intensity variations acting on the cell, and hav diaphragm to provide exposure openings of dif ing a movable contact carried by the armature, ferent sizes, the combination of an actuator mov and a pair of ?xed contacts, one engageable by 70 able in opposite directions for operating the dia the movable contact when the armature de?ects phragm to change the size of the opening; a pair in opposite directions; means mounting said ?xed of electromagnets, one for moving the actuator in contacts for movement together; a pair of relays, each direction; a photoelectric cell subject to the each in circuit with the movable contact and one same light conditions as the camera lens; a gal of the ?xed contacts of the galvanometer; a power vanometer having a movable armature electrically 5 2,388,609 connected to the cell, a movable contact carried by the armature, and a pair of relatively ?xed con tacts, one located on each side oi! the movable contact to be selectively engaged thereby depend ing upon the direction of de?ection of the arma ture; means interposed between the galvanometer contacts and the electromagnets whereby de?ec tions of the galvanometer armature in opposite directions can selectively effect energization of energization of one or the other oi.’ the electro magnets; a mounting for the two ?xed galva nometer contacts movable to shift their position in either direction relative to the ?xed contact; a cam movable with the diaphragm actuator and operatively associated with said mounting to move the latter in one direction or the other depend ing upon the direction of movement of the actu atm- and thereby causing the ?xed contacts of the one or the other of the electromagnets; a mount 10 galvanometer to shift position relative to the mov ing for the two ?xed galvanometer contacts mov able contact: and means for altering the relation able to shift their position in either direction between the cam and the diaphragm actuator. relative to the ?xed contact; and a cam movable 7. In a camera having the usual adjustable with the diaphragm actuator and operatively as diaphragm to provide exposure openings of dif sociated with said mounting to move the latter in 15 ferent sizes, the combination of a photo-electric one direction or the other depending upon the cell responsive to light conditions to which the direction of movement of the actuator so as to camera lens is subject, a galvanometer including alter the relation between the ?xed and movable a pair of relatively fixed but movable contacts and contacts of the galvanometer. a movable contact, said galvanometer being con 6. In a camera having the usual adjustable 20 nected to the cell so as to de?ect in accord with diaphragm to provide exposure openings of dif variations in voltage induced by light changes ferent sizes, the combination of an actuator mov acting upon the cell, mechanism for actuating able in opposite directions for operating the dia the camera diaphragm to expand and contract phragm to change the size of the opening; a pair the opening therethrough, electric circuit means of electromagnets, one for moving the actuator 25 including the ?xed and movable contacts selec in each direction; a photoelectric cell subject to tively responsive to de?ections in opposite direc the same light conditions as the camera lens; a tions of the galvanometer and being connected galvanometer having a movable armature elec to operate the diaphragm actuating mechanism, trically connected to the cell, a movable contact cam means movable with the camera diaphragm carried by the armature, and a pair of relatively 30 and by the diaphragm actuating mechanism, and ?xed contacts, one located on each side of the a cam follower connected to the relatively ?xed movable contact to be selectively engaged thereby contacts and actuated by the cam to maintain in depending upon the direction of de?ection of the open condition the electric circuit means when armature; means interposed between the gal the diaphragm opening is proper for the exist vanometer contacts and the electromagnets whereby de?ections of the galvanometer arma ture in opposite directions can selectively e?ect ‘ ing light conditions. ARVID I. ERICSSON.