US2574571A - Photometer - Google Patents

Description

Patented Nov. 13, 1951 UNITED STATES PATENT OFFICE PHO'IOMETER Gordon F. Laing, Delavan, Wis.

Application March 31, 1948, Serial No. 18,271

I (01.- ss-zs) film of any speed.

A feature of the invention is a standard light source comprising a fluorescent screen activated by radioactive material.

A further feature is a photometer employing a standard light source as described in the foregoing, wherein the fluorescent screen and the radioactive material, radium or the like, are in operative relation to each other only while the device is in use.

These and other features of the invention will be fully described in the ensuing specification, reference being had to the accompanying drawing, in which Fig. 1 is a back view of a photometer embodying the invention;

Fig. 2 is a side view of the same;

Fig. 3 is a rear view of the device with the back cover removed;

Fig. 4 is a section on the line 4-4, Fig. 1;

Figs. 5 and 6 correspond generally to Figs. 3 and. 4, respectively, and show a modified form of the invention; and

Fig. '7 is an enlarged view of certain parts shown in Fig. 4.

Referring to the drawing, the cup shaped body l0, having the integrally formed eye piece II, may be molded from a suitable plastic material. The eye piece II is non-concentric with the body H), as can be seen from Figs. 1 and 2. The lens I2 is mounted in the eye piece II, as seen in Fig. 4. The scale l3 carried by the body In is calibrated in accordance with various film speeds.

The ring 14 may also be molded from plastic material and is rotatable on the body H! for the purpose of adjusting the index IS with respect to the scale Is. The ring should fit rather tightly so that it will stay in adjusted position. If desired, a suitable friction device may be interposed between the ring and body. The scale l5 carried on the ring is calibrated for the different exposure times in accordance with which camera shutters are commonly adapted 'to operate.

Claims.

means of screws [8 and [9, as shown in Fig. 3.

The reference numeral 20 indicates a shoulder stud which is secured to the center of the disc I! by riveting or staking.

The back or cover 2| may be molded of plastic material like the body 10 and ring I4 and is rotatable with respect to these parts. It is held in place on the body II] by the screw 22 which is threaded into the stud 20. The scale 23 carried by the cover 2! is calibrated in accordance with a common system of stops or diaphragm apertures. The cover should have a rather easy flt so that itcan be adjusted without disturbing the adjustment of the ring M.

The plastic material from which the body HI, ring l4, and cover 2| are made may be material such as Bakelite which is opaque to light. The window 25 in the cover 2|, shown in Figs. 1 and 3, is made of transparent material such as glass or a plastic known as Lucite and may be secured in place by a suitable cement. As an al-' ternative, the cover 2| may be molded throughout of transparent material such as Lucite plastic and painted inside and out, except for the area of window '25, with black paint. The window is thus formed integrally with the rest of the cover and a stronger structure is obtained.

Directly opposite the lens E2 the disc I1 has two small circular openings 2'! and 28, shown in Figs. 4 and 7. Theopening 21 is covered by a green light filter 29 which may be made, for example, of several layers of green cellophane. The other opening 28 is covered by a fluorescent screen 30 which exhibits a green fluorescence under bombardment by radioactive material. Zinc sulphide may be employed as the fluorescent material, for example, but any suitable screen may be used and the color of the screen when activated is not necessarily green. The color of the screen and that of the filter 29 should be the same, however.

The reference numeral 3! indicates a shutter which is pivoted on the shoulder stud 20 next to the disc I1. One end of the shutter extends over the fluorescent screen 30 and carries a small disc of radioactive material 32 which is in alignment with the opening 28 when the shutter is in the position in which it is shown in Fig. 3. I

The shutter. 3 I has a limited movement determined by the length of the arcuate slot 33. The stud or pin 34 is fixed to the shutter and extends through the slot. The spring '35, a very light spring, is tensioned between the stud 34 and a pin 36 fixed to and projecting from the disc IT. The spring tends to maintain the shutter in operative position, that is, the position in which it is shown in the drawing and in which the radioactive material 32 is opposite the opening 28. The cover 21 has a pin 31, Fig. 4, for operating the shutter 3|. When the device is to be put away after use, the cover 2| is rotated in a clockwise direction as seen in Fig. 4 as far as it will go. Toward the end of this movement the pin 31 engages the tail 38 of shutter 3| and rotates the shutter on itspivot until the stud 34 reaches the end of the slot 33, where the shutter remains until the device is to be used again. In the oiT position of the shutter, the radioactive material 32 is displaced from its operative position over the opening 28 and that portion of the screen 30 which covers the opening is not subjected to irradiation.

The element 32 may be made of any suitable radioactive material capable of causing fluorescence of the screen 36 and having a long enough half life so that its decay will not appreciably change the amount of light emitted by the screen in a reasonable period of time. which has been used with excellent results is a small disc of silver impregnated with radium. The active substance may also be radium D.

The reference numeral 40 indicates a graduated light transmitting screen or light valve which is secured to the inside of the cover 2| behind window 25 in any suitable manner, as by means of cement or other adhesive. This screen comprises a plurality of sections such as A! and 42 of different light transmitting power. There may be, for example, 14 sections, of which the first section is substantially transparent while the remaining sections are progressively less so in the ratio of 2 to 1. Thus. if the numeral 1600 represents the transparency or light transmitting power of the first section, then the transparency of the second section. is 800', of the third section, 400, and so on, giving a value of .2- for the 14th section.

Screens such as 40 maybe made of sensitized film by a process of printing from a suitable negative. The negative may be made by laying out the sections on a. piece of film and masking all of the sections except one section, which is then exposed for a predetermined interval to a weak light source. The mask is then moved to uncover the second section as well as the first section and a second exposure is made. The mask is then moved again to uncover the third section and a third exposure. is made, and so on, until the last section has been uncovered and the last exposure has been made. Thus each exposure takes in one more section than the immediately preceding exposure. The first section is exposed 14 times and comes out nearly opaque when the film is developed. The last section, exposed only once, is nearly transparent and the intermediate sections have varying degrees of transparency corresponding to the values mentioned in the preceding paragraph. It will" be understood that the negative should be so made that in the positives printed therefrom the order of decreasing transparency of the sections is in the right direction. In the case of the photometer shown in the drawing the direction is clockwise in Fig. 1.

It will be seen that the screen 40 is adapted to function as a light valve, adjustable by rotation of the cover 2| to regulate the amount of light admitted to the opening 2! through the filter 29.

The operation of the photometer will now be described, it being assumed. that a. picture is to An element be taken and that the operator desires to use the photometer for selecting the stop or exposure time which is suitable for the light condition obtaining. The selection also depends on the film speed and the first step is to note the speed of the film to be used. The ring [4 is then rotated until the index I6 is opposite the numeral such as 64 on scale l3 which indicates the speed value ascertained. The ring l4 may remain in this position so long as film having the same speed is used. Some allowance can be made for special conditions, as indicated by the adjustment shown.

The operator next rotates the cover 2i, Fig. 1, in a counterclockwise direction far enough to release the shutter 3| to operative position, thereby moving the radioactive material 32 into operative relation to the fluorescent screen 39, or rather that portion of itwhich covers the opening; 23'. The rotation of the cover also moves one end of the graduated screen 40 into alignment with the opening 27 covered by the filter 29.

The operator may now bring the eye piece H to one eye and look through the photometer in the direction of the view, that is, toward the object of which a picture is to be taken, with the result that the openings 21 and 28 are seen. The lens I2 enables the eye to focus on these openings, so that the inner opening 28, the one covered by the fluorescent screen 30, appears clearly as a green spot. This is due to bombardment of the screen by alpha particles emitted by the radioactive material 32. The other opening 21 is also seen as a green spot, due to light received from outside through the graduated screen 40 and the filter 29, but is brighter or darker depending on the light condition and on the adjustment of the cover 2|. Assuming a fair amount of light and that the first section of the graduated screen 40 is aligned with the opening 21, the outer spot will be the brighter of the two. While looking at the green spots the operator proceeds to rotate the cover 2| and thus adjust the graduated screen 40 until the two spots appear to be of equal brightness or intensity.

Finally, the operator selects the value of stop or exposure time in accordance with the kind of picture to be taken and then reads the other value by reference to the scales 23 and 15. A distant view, for instance, must be taken with a small stop, or diaphragm opening, say 22, and reference to the scales shows that the proper exposure time is about second. Another picture, one which includes a moving object, requires a short exposure such as second, for which the proper stop, under conditions obtaining, is stop 8. It will be clear that in any case the result depends on the adjustment of the ring I4 in accordance with the film speed and the adjustment of the cover and graduated screen 46 in accordance with the light condition.

The modification shown in Figs. 5- and 6 may now be described briefly. The photometer is the same except for the method of operatively dissociating the radioactive material and the fiuorescent screen when the device is not in use. Whereas in the photometer as shown in Figs. 3 and 4 the radioactive material is moved away from the used portion of the screen; in the modification of Figs. 5 and 6 the radioactive material and screen are always in the same fixed relation to each other and a guard is provided which is interposed between the radioactive material and the screen except when the photometer is in use.

Referring to the drawing, the radioactive material 50 is supported on the bracket which is secured in suitable manner to the metal disc IT. The guard 52 is pivoted at 53 and is normally maintained in the position in which it is shown by the spring 54. In this position the curved end of the guard is interposed between the radioactive material 50 and the fluorescent screen 6| and is effective to prevent activation of the fluorescent material.

The operating rod 55 has a cam 56 formed at one end and extending through an opening in the disc ll adjacent the straight end of the guard 52. The spring 54 surrounds rod 55 and is compressed between the collar 51 and the disc Il' whereby the operating rod 55 is normally maintained in the position in which it is shown. An extension 58 of the rod 55 projects through the body Ill and terminates in a button 60.

When the photometer is about to be held up to the eye to make the adjustment for light value, the operator depresses the button 60 and holds it in depressed position While the adjustment is being made. The operation of rod 55 causes the cam 56 to engage the guard 52 and rotate it sufficiently to remove its curved end from between the radioactive material 50 and the screen 6|, whereby the screen is illuminated as previously described. When the operation is finished, the button 60 is released and the guard 52 is again interposed between the radioactive material and the screen, where it prevents the gradual destr'uction of the screen material which would otherwise take place.

The invention having been described that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

I claim:

1. In a photometer, a generally cup shaped casing having a rotatable cap at the open end, an opaque diaphragm in front of said cap, a viewing device including a lens mounted in the closed end of the casing and adapted to bring points on said diaphragm in focus in the eye of an observer, a body of radioactive material in said casing between said cap and said diaphragm, means comprising fluorescent material supported on said diaphragm and responsive to space bombardment from said body for producing a light spot of constant intensity visible through said viewing device, an opening in said diaphragm, means comprising a light valve in said end cap independent of said opening and adjustable by rotation of said cap to transmit outside light through the entire area of said opening to form a second light spot thereat visible through said viewing device, and a filter interposed in the path of the light passing through said opening to make said light spots of the same color.

2. In a photometer, a cylindrical shell molded of plastic material, an opaque diaphragm closing said shell at one end thereof, a viewing device including a lens at the other end of said shell, a stud or post fixed to said diaphragm at the center thereof, a cover member of molded plastic material rotatably mounted on said stud, two off center and radially spaced windows in said diaphragm, means including fluorescent material and radio-active material between said diaphragm and cover member for transmitting light through the inner said window to exhibit a light spot visible through said viewing device, a. light valve in said cover member for transmitting light through the outer said window to exhibit a second light spot visible through said viewing device, said valve being adjustable by rotation of said cover member to make said light spots of equal intensity, a ring surrounding said shell and rotatable thereon, a scale on said shell calibrated in accordance with film speeds, an index on said ring cooperating with said scale, and a pair of cooperating scales calibrated in accordance with exposure times and stops, respectively, one scale of said pair being carried on said ring and the other scale of said pair being carried on said cover member for adjustment relative to the first scale of the pair by rotation of said cover member to adjust said light valve.

3. In a photometer, a substantially straight tubular casing, an opaque member extending across said casing inside thereof and forming a partition, said partition having first and second spaced openings therein side by side and in the same plane, a device including a lens at one end of said casing for viewing said openings, fluorescent material covering the first opening on the side of said partition opposite from said viewingdevice, radioactive material inside said casing causing said fluorescent material to emit light to thereby illuminate the whole area of said first opening and cause the same to be visible in said viewing device, a filter covering the second said opening and adapted to transmit light of the same color as the light emitted by said fluorescent material, a graduated light valve at the other end of said casing for admitting light to said filter and second opening from outside the photometer, and means for adjusting said light valve to cause said openings to be illuminated with equal intensity.

4. In a photometer, a tubular casing, a viewing device mounted at one end of said casing for use in observing the interior thereof, means including a body of radioactive material and a fluorescent screen inside said casing for producing a spot of light of constant intensity in the range of said viewing device, means for producing a second spot of light along side said first spot, said last means including a rotatable light valve at the other end of said casing for admitting light thereto, said light valve having a closed position and a plurality of open positions in which it admits different amounts of light to said casing, a movable member supporting said body, said member having a first position in which said body is operatively related to said screen and a second position in which said body is displaced from said screen sufficient to prevent activation thereof, means operated by rotation of said light valve to its closed position to engage and move said member to its second position, and means responsive to rotation of said light valve to any open position to restore said member to its first position.

5. In a photometer, a cylindrical housing, an opaque diaphragm closing said housing at one end thereof, a viewing device including a lens at the other end of said housing, a stud or post fixed to said diaphragm at the center thereof, a cover member rotatably mounted on said stud, two off center and radially spaced windows in said diaphragm, means including fluorescent material and radio-active material between said diaphragm and cover member for transmitting light through the inner said window to exhibit a light spot visible through said viewing device, a light valve in said cover member for transmitting light through the outer said window to exhibit a second light spot visible through said viewing device, said valve being adjustable by rotation of said cover member to make said light spots of '7 equal intensity, a ring surrounding said housing and rotatable thereon, elements comprising an index and a scale calibrated in accordance with film speeds, one of said elements being carried on said ring and the other being carried on said housing, whereby said elements are relatively adjustable by rotation of said ring, and a pair of co- .operating scales calibrated in accordance with exposure times and stops, respectively, one scale of said pair being carried on said ring and the other scale of said pair being carried on Said cover member for adjustment relative to the first scale of the pair by rotation of said cover member to adjust said light valve.

6. In a photometer, a housing, alight standard within the housing comprising a fluorescent screen and a radioactive element, said screen being adapted to emit visible light under exposure to emission from said radio-active element, an optical device including an eye piece in said housing providing a path of observation of said screen presenting an image of the same to a viewer, a light valve for admitting a beam of light to said housing and directing the same to a position adjacent said screen within range of view through said eye piece for comparison with the light emitted by said screen, said light valve including a member shiftable to vary the intensity of light admitted, said shiftable member having a plurality of active positions and an inactive position, and means cooperatively relating said shiftable member and said light standard and comprising a member movable in response to movement of said shiftable member to exclude access to said screen of emission from said radio-active element when said shiitable member is in inactive position.

7. In a photometer, a housing, a light standard within said housing comprising two elements of which one element is a fluorescent screen adapted to emit visible light upon exposure to radio-active emission and the other element is a radio-active body, one of said elements being movable between a first position in which said screen is exposed to activating emission from said body and a second position in which said screen is deprived of activating emission from said body, optical means including an eye piece in said housing providing a path of observation of said screen presenting an image of the same '8 and means responsive to movement of said shiftable member for producing a coordinated movement of said movable element to maintain the same in its first position when said beam is on and in its second position when said beam is off.

8. In a photometer, a casing, fluorescent material inside said casing, radio-active material inside said casing and operatively related to said fluorescent material to cause a surface thereof to emit light of substantially constant intensity, a comparison screen of light filtering material mounted in said casing adjacent to and in substantially the same plane as said light emitting surface, said screen being adapted to transmit light of the same color as that emitted by said surface, an adjustable light valve admitting light from outside said casing to illuminate said. screen, a viewing device including a lens in said casing through which said surface and screen may be observed, and interposed opaque masking means inte cepting all the light transmitted toward said viewing device from said surface and screen except that transmitted by predetermined, limited, and sharply defined areas thereof which are visible in said viewing device as separate spots of light, said spots being spaced apart a substantial distance by a dark area which is continuous with a dark area surrounding both said spots.

9. A photometer as claimed in claim 8, wherein the visible areas are of substantially the same size and are spaced apart a distance not less than a major fraction of the smallest dimension'of said areas.

10. A photometer as claimed in claim 8, wherein the visible areas are circular and of approximately the same size and are spaced apart a distance which is approximately equal to the diarneter of one of said areas.

GORDON F.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 445,743 Ballard Feb. 3, 1891 1,351,999 Howenstine Dec. 14, 1920 1,990,022 Du Mend et al. Feb. 5, 1935 2,074,226 Kunz et al Mar. 16, 1937 2,47 6,340 Wallhausen July 19, 1949 FOREIGN PATENTS Number Country Date 214,670 Germany Oct. 18, 1909 298,762 Germany June 27, 1917 754,347 France Nov. 6, 1933

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