US2153165A - Photometer - Google Patents

Description

April 4, 1939. E. T. TURNEY 2,153,165

' PHOTOMETER Fi led May 10, 1938 INVENTOR. flagella ZTanmgy,

BY Ww TTRN.

. Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE Application May 10, 1e: 32:31). 206,981

ZCIaims.

The invention herein disclosed relates to photometers.

, Special objects of the invention are to provide a relatively simple, inexpensive and atthe same time a. thoroughly practical device, which will show instantly and accurately the proper exposure and which will be of a small compact form, adapted to be easily and conveniently carried about.

The foregoing and other desirable objects are attained by the novel features of construction, combinations and relation of parts hereinafter described, illustrated in the accompanying drawing'and broadly covered in the claims.

The drawing accompanying and forming part of the specification illustrates one'practical embodiment of the invention. The structure however may be variously modified and changed, all within the true intent and broad scope of the 20 claims.

Fig. .1 is a front view of the device and Fig. 2 is a rear view of the same.

Fig. 3 is an enlarged and partly broken view of the base portion of the article, with the cover 25 removed.

Fig. 4 is a longitudinal sebtional view on sub w stantially the plane of'line 4-4 of Fig. 1. Fig. 5 is a broken sectional detail of the switch mechanism as on substantially the line 5-5 of Fig.3.

In the present invention, a proper exposure is instantly ascertained by regulating the intensity of a standard light to match existing light conditions and then comparing the reading of the 35 regulator with an exposure scale, laid off in units corresponding to the units of regulation or adiustment of the standard light.

In the illustration, the standard light 'is provided by a small lamp bulb 'i, Fig. 4, enclosed 40 within a case and placed to illuminate a screen which is exposed to surrounding light. The light screen is shown as composed of a color filter 8,

and a diffusing disc 9 of frosted glass or the like, these being confined between aperture defining 45 'plates or washers i0, H, in' front and back of the same,,within a tube l2, surround ng the bulb. This light tube is shown as supported at the back by a sleeve i3, set in the front cover it, of the casingand a telescopically related viewing tube 50 I5, is shown as slidingly interposed between'this outer tube i3 and the inner light tube l2.

The electrical energy for the lamp is provided in the illustration by two dry cells i6, i6, removably held in the terminal clips l1, l8, i9, 20,

'of the other dry cell.

The circuit may be traced from the upper clip l'l, through connecting strip 2!, to center terminal 22, or the lamp socket and from the screw terminal 23 of the lamp socket by wire 24, to the resistance wire 25 of a current compensating reg- 5 ulator, thence by the brush 26 and spindle 21,01 said regulator and strap 28, to the upper clip l9, From the lower clip 20, of said second dry cell, the circuit is completed by connection 29, to resistance wire 30, of the cali- 10 brating regulator and which latter has a brush 3 I and a spindle 32, which-at the back is engaged by a'spring strip 33, to which is connected one end of a spring switch contact 34, which can be depressed by button 35, into engagement with the base of the other, lower dry cell clip 13.

The spindle of the light intensity regulator is shown as carrying a finger disc 36, calibrated at 3], for registry with an index 38.

Similarly, the spindle 21, of the balancing resistance is shown as having a thumb tum' 39, with a line or pointer Ml, which may be associated with a scale or simple index mark 4|.

The markings on the scale 31, of the regulator are calibrated to match the exposure values of a scale such as illustrated at 42, Fig. 2, located on the back or some other conveniently readable position on the casing.

In the present illustrated embodiment of the invention all parts, of the device except the light tube and telescopic extension are mounted on the base or back 43, of the instrument case. Thus as shown in Fig. 4, the front of the case is simply a hollow cover fitting over a shouldered portion 44, oi. the base, removably rtained by spring clips 45, 46, and having openings 41, 43, d9, 50, of a size to pass the thumb turns or buttons 39, 3t, 35, respectively.

The instrument is first standardized, as when inserting new dry cells, by comparison with a known light source such for example as a 40 watt electric lamp. This is accomplished by exposing the light screen to the standard light source and then adjusting the knob 39, of the compensating resistance until the instrument light is no longer apparent through the screen, when the switch'button is depressed. This is readily observable by pushing the switch button to flash the light and turning the compensator to trim down the intensity until the light just disappears and no longer flashes when the button is depressed. This simple standardizing step may be performed from time to time to compen sate for loss of battery strength. 7

In use the unit is held so that the light screen is exposed to the surrounding light and at the same time may be readily observed. with the switch button held in, the main regulator may then be adJusted until the internal light on the screen just disappears. Then if no light appears when the switch button is "flashed one or more times, it will be known that the proper adjustment has been reached. The number which then appears at or nearest the index on the regulating scale is observed, and then located on the exposure scale 42, on the back of the instrument,

where it shows on the scale the requisite exposure factors for existing conditions, such as extent and duration of exposure.

The battery compensator is in series at all times, so a standardizing adjustment may be made whenever considered necessary or desirable.

The battery drain is so slight that small size cells may be used and these in the symmetrically balanced relation indicated small space and canbe quickly removed and replaced when the cover is slipped oil. the base. The sliding hood or shield it, while not always necessary is desirable under certain light conditions, where it is diflicult to be sure that the adjusted light is balanced with the outside light. The color filter 8, may be green or other tint and if desired, this may be made relatively removable as by being clamped in place between the end of a liner 5|, within tube i2, and a finishing ring 52, screwed or otherwise removably engaged in the outer end of the tube, these cooperating to clamp the rings H), II, and interposed screen layers ll, 9, between them. Consisting as it does of but few small parts which can be compactly related, the instrument can be made quite small and light and of a size to be readily carried in the pocket.

in Fig. 3, occupy r thereby standardize the instrument and sepa-,

rate independently adjustable resistance means in said case and connected in said battery circuit for regulating the intensity of said light source to match surrounding light conditions as observable on said light screen.

2. A complete, unitary, portable photometer, comprising a small hand case provided with a light screen, a light source in said case back of said light screen and including an electric lamp and a battery in circuit relation therewith, resistance means in said case and connected in said battery circuit for balancing the intensity of said light sourceas appearing at said light screen with the intensity of a standard light source to thereby standardize the instrument and separate independently adjustable resistance means in said case and connected in said battery circuit for regulating the intensity of said light source to match surrounding light conditions as observable on said light screen, said standardizing means and said second regulating means being in series relation in said battery circuit and switch means on the case in said battery circuit for flashing the light source as so standardized and as so regulated to match surrounding light conditions.

EUGENE T. 'I'URNEY.

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