US1688081A - Transmission of pictures by electricity - Google Patents

Description

Y T ,I 0 I R T C E.. L E5 Mw 1 s :v -M2' lm-h.. .Tm E wa HPM d we NH.. .OF I. s s I M s N A R TL Oct. 16,v l 928.

Patented Oct. `16', 1.928.

UNITED STATES '1,688,081 PATENT OFFICE.

HERBERT E. IvEs, or MoNTbLAIR, NEW JERSEY, AssICNoR, BY MEsNEJAssIGNMEN'rs, I To WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION or NEW YORK.

AIIJEtAlQ'SlYIISSION 0F PICTURES BY ELECTRICITY.

Application filed March 2, 1.925. Serial No. 12,693. I

This invention relates to picture transmission apparatus and more particularly to the optical system employed in reproducing pictures transmitted by electrical means.

In applicants Patents, Nos. 1,667 ,805 and 1,683,976, granted May 1, 1928, and Sept. 11, 1928, res'pectively, two forms of reproducing systems are ,described which are adapted for the reproduction of electrically transmitted pictures. In the first of these the reproduced pictures are composed of p successive lines or traces ofvarying width, while in the second the successivetraces are of constant width but varying in density along the trace.

The reproduced picture in both instances is composed; of exposed areas, which are. separate and distinct from one another and give a grained appearance to the picture. l

An object of the present invention is \to I0 improve thefaithfulness of reproduction of pictures transmitted electrically.

Another object is to double or oyerlap successive exposure so as to produce a picture more nearly like the original.

' 25 In the attainment of these objects according to one embodiment of the invention the exposure of the recording iilm is controlled by a light valve which itself is energized by a carrier wave modulated in accordance with the :tone values of elemental areas-.of the picture to be transmitted.y Interposed in the light path from the light valve to the recording Elm -is double image producing element, such as a piece'of Iceland spar. The record- 15 ing film moves relatively to the light valvel aperture and for each exposure of the recording film a double image of the aperture is obtained. Means are also provided to produce overlapping of successive exposures.

4u Substantially grainless reproductions from the standpoint of the lay observer are thus obtained, the texture of the reproduction being observable only under a microscope.

Other objects and advantages of the invention will become apparent from the following. descriptionand drawings: Fig. l is a digrammatic view of an optical `system embodying the' present invention. Fig. 2 shows onetype-of optical system to which the linvention is applicable. Fig. -3

illustrates an enlarged portion of a picture, composed of lines of varying width. Fig. 4 illustrates the same portion produced by means ofg-the optical system of this invention.

66 Fig. 5 is adiagrammatic view similarto Fig. ventionI the recording beam of light passes 110 f 2 embodying a modification of the invention.

Fig. 6 illustrates a cross section of another y type of picture as reproduced according tol the system of Fig. '5. Fig. 7 illustrates a cylindrical lens as used in a furtherl modifica-a 60,

tion of the invention. Fig. 8 illustrates a crossA section of a picture `produced using the lensshown in Fig.\7.

Like elements in the several iigures are designated by identical reference characters. The present invention is applicable to any type of picture transmission system which reproduces pictures, writing or other elec,- trically transmitted subjects by means of an -foptical system. Two suitable optical sys-f 7" tems are disclosedinapplicants patents, referred to above. The-typical optical systeml illustrated in Fig. 2, consists of a light source 12 and a concentrating lens 13 for focusing light upon 'the aperture of a light valve V together with a projecting lens 19 As shown in Fig. 2=this light/#valve comprises a field magnet 15 and a string shutter element 16 in circuit with a transformer 17 Carrier current signals impressed on transformer' 17 cause currentJ fluctuations in the light Valve string 16 which is vibrated from side to side exposingthe' light aperture first on one lside of the string and then on the other. Light passing the light valve shutter varies iin intensity corresponding to the amplitude of the carrier wave. This light is focused on a rotating recording drum 18 by means of lens 19. v Y

Since the string of the light valve vibrates in a direction perpendicular to the trace on the recording, drum the resulting picture `will be composed of lines ofv varying' width as illustrated in Fig. 3 and more fully described in applicants Patent No. 1,667,805 referred 5 in the optical system some means for forming 100 a double image of the light valve aperture Von the recording cylinder such asa splitlens or heliometer, a bi-prism or preferably piecet of double refracting Iceland spar.

will bejormed close together on the recording element., In forming the portion of a picture illus' any case two separate and distinct images y trated in Fig, 3 according to the present inthrough a piece of Iceland spar as shown in Fig. l. Each image is therefore formed twice as indicated at A and A', B and B',

etc., in Fig. 4 and F and F in Fig.n 1. The

- inch in thepreproduction, but actually in` creases the resolving power of the optical system. This is seen by comparing the lines in Fig. 4, which are composed of B and A', B and C, and C and D. The line B-Q of Fig. 4 is the same as the line B-C of Fig. 3, but there is no duplication of this line,

. since the half line B, which is identical with B, is associatedwith the half line A In the same way the half line C, identical with C, is associated with the half line D. It is, therefore, seen that no 'two lines are alike and four such lines are formed instead of two. Upon examination, it is noted that the light areas between the successive dark lines are duplicated whilev the dark areas are all different, Thus it will be seen that the light areas I-I and I-I are identical, and K and-K are identical. From this it is apparent that the resolving power of the optical system is increased by In the case of anoptical system, asf described in applicants Patent No. 1,683,976, referred to above, the reproduction is composed of a series of exposures along the trace which corres ond in density to the full line in Fig. .6. uch an optical system is illustrated in Fig. 5.V7 In this case the string of the light valve vibrates in the direction of the ytrace on. the recordin film. For the purpose of illustration the ouble'image element is shown as a so-called bi-prism formed integral with the ylens 22 so that the combination as shown in Fig. 5 has a curved lens surface 23' facing the recordingfilm and an T opposite face composed of two sections 24 .and 25 at a small angle'to each other. 'a lensy forms two distinct images of the light Such l Valve onrthe recording film. When a double image element is employed in combination with the optical system of Fig. 2 successive imagesare displaced by half an exposure interval, so'that instead of simple exposures a, b and c, shown Ain full lines in Fig. 6, there is formed on the recording element a series of overlappingI or double exposures corresponding to M', 6 5', e-c, etc., the

second exposure being indicated by\ the broken-line inFig. 6. The resulting exposure has none of the grained effect ofthe pictures formed by other methods of reproduction. By overlapping the exposures the no exposure. portion between half cycle exposures are eliminated forming a true half-tone picture similar tothe original.

The double image forming elements are interchangeable in the optical' systems shown in Figs, l and 5. That is a bi-prism, a splitlens, o`r a piece of Iceland spar,may beused in either system as desired, or any other double image formino element or combination maybe employed. Y

In order to `insure the proper positioning of successive overlapping images in using Iceland spar the crystal is mounted so that it may be turned about its axis. In this way the separation of the ordinary and the extraordinary ray may be varied at will. As illustrated in Fi l the crystal is mounted n a pivot 27 an adjusted to the proper angular position by screw`28.

Another means for producing a somewhat similar effect is illustrated in F ig. 7 In this case a cylindrical lens is employed for distorting the image by spreading the beam of light along the trace instead of focusing at a point. In this case t-he successive eX- posures'overlap, as shown in Fig. 8, so that Y ing or reproducing mechanism, whether used in picture transmission or in any other manner for reproducing pictures, writing, etc.

What is claimed is:

l. An optical system for use in picture transmission comprising a double light refrac-ting image forming element.

QVTheAcOmbination with light sensitive means of electro-optical means fory exposing said lightsensitive means in successive duplicate sets of lines to cause adjacent non-duplicate lines to overlap. y f 3. The combination with. light sensitive means of electro-optical' means lfor exposing said light sensitive means inadjacent` pairs of lines to cause adjacent lines of said adjacent pairs to overlap.

, 4c. In an optical system comprising a light.

source, a recording element, and alight valve having a yariable IAaperture for controlling the light falling upon the recording element,

`means for forming an image of said light valve aperture on the recording element and other means for doubling the image formed.

5. In an optical system for picture transmission apparatus, means for forming an image on arecording element, andra piece of Iceland spar for doubling said image.

6. The method of producing pictures which comprises modulating a beam of light, forming an image in accordance with said beam, doubly refracting the image formed, and recording impressions on said refracted images to form a picture.

7. In an optical system, a light source means for forming successive images of sai light source in pairs on a recbrding lm, and means for causing overlapping of images of .adjacent pairs on the recording ilm.

8. In an optical system a double image forming element, and means to adjust the angle of incidence of rays of' light on said double image forming element, whereby the separation of the emergent rays is controlled.

9; The combination with a picture receiving surface of electro-optical means for producing thereon a picture composed of a plurallty of similar series of exposures.

10. In an electro-optical system for producing an image of an object, means u on which the image is to be produced, and e ectro-optical -means for simultaneously lait'ecting a plurality of non-contiguous elemental HERBERT E. IVES.'

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