US2240844A - Picture projection - Google Patents

Description

May 6 1941- J. F. GoGGxN Al. 2,240,844

' PICTURE PROJECTION Filed May 21, 1958 2 sheetssheet 2 /A/GEAS/N PARTS 0F /UNS PER /000 Flm Pim/MR TIE-5 HALL A TTORNEY Patented May 6, 1941 islidiTE Silit? Eid PECTURE PRJECTIN Jeremiah F. Goggin, Moline, Ill., and Ray E. Hall, Davenport, iowa 3 yClaims.

The present invention relates to the art of picture projection and more particularly to processes and apparatus for the projection of pictures upon a screen, for instance, motion pictures or other serially projected pictures.

It is an object of this invention to provide a process and apparatus for picture projection in which light emitted by the screen, in distinction to light reflected by the screen, is seen by persons watching the screen.

A further object is the provision oi a process and apparatus whereby non-visible photons projected on the screen may he employed in the production of pictures or other images on the screen.

ln accor-dance with the present invention, photons in organized arrangement and intensity are projected on a screen which comprises a support and a luminescent material so posititicned on the support that light emitted thereby is visible.

Other objects and advantages of this invention will be explained in and be obvious from the iollowing description taken in conjunction with the accompanying drawings forming a part of this application. In the drawings,

Fig. i is a graphical illustration of the effect of the wave length of activating light on the period and intensity of phosphorescence,

Fig. 2 is a graphical illustration of the eiect of varying the intensity of red light in any given activating light on the period and intensity of phosphorescence,

Fig. 3 is a graphical illustration oi the eiect of varying the intensity oi red light in any given activating light on the intensity of fluorescence,

Fig. 4 is a graphical illustration with various activators of the effect of changes in the concentration of the activators on the period of phosphorescence,

Fig. 5 is a graphical illustration o the effect on the wave length of emitted light of changes in the concentration of various activators, and

Fig. 6 is a diagrammatic illustration of apparatus in accordance with this invention. and suitable for the periormance of the process hereof.

Within the scope or" the present invention, the luminescent material employed may be either a fluorescent material or a phosphorescent material. ln order to explain the relationship of these materials, the fluorescent materials applicable to the present invention may loe any type, such as the oxide type, for instance, calcium. tungstate or Zinc orthosilicate, the sulde type, for instance, the sulde of calcium, zinc, barium or strontium, or the fluorescent dye type, for instance, fluorescein or eosin. The most effective phosphorescent materials are in general quite similar to the sul- :ide type of fluorescent materials. This type of terial, termed a phosohon is crystalline and the primary present contains suitable impurities which act as activators. These ircpuritics are perhaps distributed throughout the crystal lattice. When less than a critical amount oi any particular activator or group o activators is present, the phosphor is liuorescent. When more than that critical amount is present, the phosphor exhibits the additional phenomenon of phosphorescence. For purposes of convenience in this application, the term fluorescent material is not used in its generic sense but is used to indicate iiuorescent materials which do not also phosphoresce, ard phosphorescent material is used to indi. tV materials which exhibit the phenomenon oi pncsphorescence.

Considering now the question of emission spectra ci' luminescent materials, both fluorescent materials and phosphorescent materials luminesce during absorption of photonic energy. For fluorescent materials, the time constant oi decay, i. e., the time the material iiuoresces alter ahsorption ceases, is short, being on the ori-er of 5x10-5 seconds or less.

On the other hand, the natural period of decay of phosphorescence oi any particular phosn phorescent material is ol quite substantial duration in comparison with the constant of decay of fluorescence, the natural period depending upon the composition of the phosphor. As graphically illustrated in Fig. ll, the natural period of decay is a iunction or" the activator, the period increasing from that for manganese as the activator through the series manganese, copper, tin7 cadmium, sodium, antiinony, potassium, lithium, and bismuth, the last giving the longest natural period of decay of those named. Fig. 4-4 also illustrates the fact that the natural period of decay is a function of the arnount of activator present, the period with each activator increasing from a period near zer with increasing concentration to a maximum period, after which further increases reduce the period toward Zero.

For any given phosphor of the phosphorescent type, the period of decay can, however, he controlled by controlling the composition oi the activating light. Thus, as graphically illustrated in Fig. l, increasing the wave length of the activating light decreases the period of decay. It may therefore be seen that the period of decay of phosphorescent material may be controlled by controlling the composition of the activating light.

One application of this invention involves the use of a fluorescent material in combination with a projection screen. Rays of photons are organized into a series of related arrangements and the series focused on the screen. While Within the scope of this invention, the photons may be of Wave length between about one thousand (1,000) Angstrm units and the far infrared, which is the sence in which the term photon is herein used, a preferred application of the invention involves the use of photons in the nonvisible, ultraviolet range. The series of related arrangements may be such as a conventional motion picture. This results in non-visible light being projected on the screen and the picture or the like being viewed by light emitted by the screen instead of by light reflected from the screen. This we have found is extremely advantageous as it produces a light which can be seen much better at an angle than the now customary reflected light, and the intensity of light from screen is greater in proportion to the light projected on the screen. The source of light should be rich in ultraviolet wave lengths and may be produced by a non-filament type of lamp,

such as a mercury vapor lamp, though it is desirable to have the lamp emit some visible light, since, as graphically illustrated in Fig. 3, when long wave length light is added to an activating light, which in other respects remains constant, the intensity of the emission increases.

As well as increasing the intensity of the emission, the visible longer wave length light may be controlled, as by the use of filters or by suitable noble gases in the lamp envelope, so that in case the emitted light is not white but is colored, the emitted light plus the reflected light is white or unobjecticnable in color. It should be noted, however, that the use of reflected visible light is not essential to obtaining substantially white light. 5 illustrates the range of wave length emitted by phosphors of varying activator content. The activators may be selected and a mixture thereof employed so as to give a substantially white emission from the projection screen.

Regardless of the specific form in which the invention is applied when an activating light predominantly ultraviolet, as from a non-filament type of lamp, is employed, the nre hazard is substantially eliminated and it is unnecessary to employ expensive non-flammable film material.

If preferred, the projected light employed may be predominately of visible wave lengths, a lament lamp being employed and the light from the screen being composed of both reflected and emitted light.

In accordance with another form of thc invention, the luminescent material employed on the projection screen is of the phosphorescent type. The remainder of the process of projection may be the same as when the fluorescent type of material is used, as above described, and the advantages derived are the same. However, certain refinements and improvements thereover are possible by the use of the phosphorescent type of material.

With modern projection machines, the interval between frames has been reduced to about GX3 seconds, whereas on the old types of machines the interval is much greater. It has been found that the strain on the eyes caused by motion pictures is not due to the changing from one picture to another but is due to the change in intensity of the light during the interval. The

eyes of the observer, when the light ceases even for the short interval between frames, start moving to accommodate themselves to the diminished intensity, and then the process is immediately reversed.

Since the constant of decay of fluorescence is somewhat less than 5 105 seconds, the fluorescent type of material does not emit light for over one hundredth of the present interval. This is insufficient to have any appreciable effect in reducing the strain on the eyes. On the other hand, the period of decay of a phosphorescent material may be controlled from the constant of decay of fluorescence upward to several hours by controlling the amount and composition of the activating light. Such a reduction of the period of decay from the natural period is hereinafter termed accelerated phosphorescence.

A series of photon images are organized and projected onto `a screen carrying a phosphorescent material. rihe wave lengths of the photons are controlled as by the light source and by light filters to transmit bands of light to accelerate the phosphorescence. Thus, to illustrate, the wave lengths may be controlled so as to contain sufficient long wave photons that ithe phosphorescence is of suniciently short duration that the projected images do not blur but blend one into another. For instance, with motion pictures it is desirable for the phosphorescence to last from the end of one frame to the beginning of the next. As graphically illustrated in Fig. 2, when phosphorescence is accelerated with the long wave light, the intensity of the luminescence increases. By this process, We have obtained motion pictures which cause no strain on the eyes and, additionally, for some reason which is as yet inexplicable, pictures are thereby produced which have greater depth than when shown with ordinary projector and screen using reflected light exclusively. The phosphorescent emitted light between frames is not exclusively for the showing of images; it also illuminates the screen between frames so that the light intensity is substantially constant. For this reason, the period of decay need not be exactly equal to the time between frames but the period may extend into the subsequent frame or frames without blurring of the pictures.

Ii desired, the invention may be applied to motion pictures in the following manner. Light may be condensed and organized into images by a lm carryinT a plurality of frames. The images may be then projected on a screen carrying a phosphorescent material. The light may be predominantly ultraviolet but contain about rive to ten per cent of red. The phosphor may be such as described in the copending application, Serial No. 204,628, of Jeremiah F. Goggin, one `of the present applicants, for producing a blue light. In this way, motion pictures may be produced primarily by light emitted from the screen, the period of decay being decreased and the intensity increased by red light being projected on the screen.

rEhe present invention in its broad aspect also has application to the projection of a series of stereoscopic pictures. rIhe light employed may be of such wave length that the phosphorescence from the screen which carries a phosphorescent material is activated only enough so that the image seen on the screen is visible to or through the subsequent picture. By having it visible during the time the following picture is projected on the screen, comparison of pictures is made possible.

The following apparatus is characteristic of apparatus which may be used to carry out the above processes. A source of light I which may be either a filament or non-filament lamp emits light which is condensed by the condenser 2 and filtered by suitable light filter 3. The filtered light passes through and is organized as a series of images by a suitable iilm 4 moved step by step by means of conventional mechanism, not shown. An object lens 5 is positioned to focus the light on screen 6. The condenser 2, iilm 4, and object lens 5 are constructed to transmit the desired Wave length, including in general .the ultraviolet. The screen comprises a support 6 which carries a luminescent material 1 exposed to the light from the projector and in a position to be visible to those viewing the picture. While the invention includes the use of a lament type lamp, one of .the features of the invention is the adaptability of non-filament lamps hereto. This allows operation at low temperatures so that the lm need not be of reproof material, whereby the lire hazard is almost entirely eliminated.

Having now described our invention, we claim:

1. In the art of picture projection, the process which comprises organizing serially a plurality of arrangements of photonic rays predominantly ultraviolet and serially projecting said arrangements onto a screen comprising a support and a phosphorescent material, said serial arrangements being spaced and said photonic rays containing a suiclent intensity of long wave length rays to accelerate the phosphorescence to such a degree that the period thereof is about the length of the spacing between said arrangements.

2. In the art of picture projection which comprises organizing serially a plurality of arrangements of photonic rays, and serially projecting said arrangements onto a surface coated with phosphorescent material, said serial arrangements being spaced, regulating the intensities of the Various wave lengths of the components of said photonic rays to ycontain a predominance of short Wave length rays to produce substantial activation of said material and suil'icient long wave length rays to accelerate the phosphorescence to such la degree that the period thereof is about the length of the spacing between arrangements.

3. In the art of picture projection involving serially projecting a plurality of arrangements of photonic rays, which serial arrangements are spaced and involving the projection thereof upon a phosphorescent screen with the photonic rays employed being predominately short wave length, the method of controlling the period of phosphorescence which comprises vadding to the short Wave length rays a suicient proportion of long wave length rays to adjust the period of phosphorescence to a point such that it is substantially equal in length to the spacing between arrangements.

JEREMIAI-I F. GOGGIN. RAY E. HALL.

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