US2456052A - Curtain for focal plane shutters - Google Patents

Description

Dec. 14, 1948. 1 W DOYLE ET AL 2,456,052

CURTAIN FOR FOCAL PLANE SHUTTERS Filed Nov. 2, 1944 ATTO NEYS Patented Dec. 14, i948 UNITED STATES PATENT i OFFICE CURTAIN FOR FOCAL PLANE SHUTTERS `Irving W. Doyle, Massapequa, and Carl V. Johnson, Kew Gardens, N. Y., assignors to Fairchild Camera and Instrument Corporation, Jamaica, N. Y., a corporation of Delaware Application November 2, 1944, Serial No. 561,556

3 Claims. 1

This invention relates to a curtain for a focal plane shutter.

As fixed slit focal plane shutters are capable of speeds in excess of a thousandth of a second, their curtains must be capable of withstanding substantial stresses and forces to which they are subjected throughout a complete cycle of operation. During the winding portion of the cycle, the full bias of the shutter spring is exerted on the curtain which, for the sake of manufacturing expediency, is customarily made in two parts joined together at the slit. When an exposure is made at high speed, the full force of the spring is suddenly exerted on the curtain so as to sweep its slit across the focal plane. Although the curtain and its associated parts are relatively light in Weight, they have, however, Sufiicient inertia and gain sui'licient momentum, to cause undesirable exposure conditions. These conditions often result in improperly exposed negatives, particularly in the case of aerial photography, where in many cases extreme accuracy of reproduction is prerequisite.

Thus, if the width of the curtain slit varies during the exposure, the negative is not uniformly exposed. inasmuch as the curtain slit is customarily formed by spaced relatively rigid strips of metal or the like, these strips, because of their necessary light weight, are characterized by a certain amount of resiliency. Thus when the curtain, and accordingly the strips, move at high speed across the focal plane, the force of the shutter spring` may be transmitted through the curtain to one or both of the slit forming strips, thereby causing relative movement between the strips during their exposure movement.

It is accordingly among the objects of this invention to provide a curtain for a focal plane shutter which, While simple, inexpensive and rugged in construction, yet overcomes the above disadvantages in addition to others in an eilicient and practical manner.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, as will be exemplified in the structure to be hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the drawing, wherein there is shown one form of the invention,

Figure 1 is a top plan view of the shutter with a portion broken away to show a driving spring;

Figure 2 is a fragmentary top plan view of one of the shutter curtains;

Figure 3 is a substantially enlarged section taken along the line 3 3 of Figure 1; and

Figure 4 is a substantially enlarged section taken along the line 4--4 of Figure 1.

Similar reference characters refer to similar parts throughout the various views of the drawing.

In Figure l, a shutter is generally indicated at Il! and includes a pair of curtains II and I2, joined together at their ends which are spaced a suitable amount to provide an exposing slit I3. The opposite ends of curtains II and I2 are secured to rollers I4 and I5, one or the other of which may include a conventional operating spring Ida which, when the shutter is released for operation, draws slit I3 across the focal plane aperture which lies between rollers I4 and I5.

Curtains I I and I2 are identical in all respects, and accordingly for brevity we have shown in Figure 2 curtain I2. This curtain may be formed of any suitable opaque material, preferably a finely woven fabric which may be suitably treated to assure complete opacity. At the slit forming end of the curtain are a pair of tabs I6 and I'I by which curtain I2 is attached to curtain I I (Figure 1) in a manner to be hereinafter described, to form slit I 3.

Referring back to Figure 2, the fabric between tabs I and II is slit as at 4U and 4I and is cut on a radius to provide a curved end portion I8 to which is fastened a metal strip I 9. Strip I9 is U-shaped in cross section and accordingly, as may be seen in Figure 4, comprises top and bottom flaps 20 and 2I, and a bight 22. The ends of strip I 9 (Figure 1) are so formed as to provide spaced attaching ears as, for example, ears 23 and 24 (Figure 3), through which a rivet 25 extends to fasten the end of the strip to curtain tab Il of curtain I2, as well as curtain tab ISa of curtain II. The other end of slit strip I 9 (Figure 1) is similarly attached to the other overlying tabs of curtains II and I2. The portion of strip I9 between its ends has disposed therewithin the curved edge I8 (Figure 4) of curtain I2, which may be wrapped around a small rod 26 which lies Within the bight 22 of the strip` When this curved edge of the curtain is installed about rod 26 Within the strip, the central portion of the curtain is dra-wn away from the strip, while the ends of the curtain edge are held so that loose folds 21 (Figure 1) of the curtain fabric are formed centrally thereof. The edge of the curtain may be secured within strip I9 in any suitable fashion, as by cementing the fabric therewithin.

attacca Curtain I is similarly attached to a strip 28, the ends of which are fastened to the curtain tabs in the same manner as described hereinabove With respect to the joint shown in Figure 3. Thus the overlying curtain tabs 16a and I'I are held against separation by two rivets 25 (Figure l) and the J'oint thus formed has stitched thereto overlying and underlying strips Eli and dll (Figure 3) of any suitable material, these strips being stitched to the curtain tabs as shown at 3l in Figure 1.

It Will now appear that the two curtains I l and l2 are securely fastened together at the ends of slit I3, and also that the strips it and 23 which form slit i3 are fastened to the curtains in accu# rately dimensioned spaced relationship, wherein they are held substantially immovable relative to one another by reason of the nature of their attachment to the curtains, and. by reason of their inherent substantial rigidity resulting from their U-s'hap'ed cross section, as well as the rods, such as rod 26 (Figure 4) lying in the bight of each; Curtain Il is, of course, fastened to strip 28 in thesame manner as described with respect to curtain I2 and strip IS, so that loose folds 32 of material are formed at the central portion of the curtain adj acent the edge thereof.

Wln curtains i i and i2 are mounted on rollers I 4 and I5, the shutter operating spring in one of the rollers draws the two curtains taut so that they lie llat adjacent the focal plane. Through the provision of the loose portions or folds 21 and 3,2 vin the curtains the tension of the shutter spring is to a substantial extent absorbed by the fabric of the curtains before being exerted on the central portions of strips i@ and 28. Otherwise, the spring bias would bow the central portions of te strips away from one another, thus imparting to the opposite edges of slit i3 a curvature rendering the slit width non-uniform. By the same token, the sudden pressure of the shutter spring on the curtain when an exposure is made is substantially absorbed by these loose curtain portions, with the result that there is little or no relative movement between the slit forming strips length of said curtain While motionless at its longitudinal center line being greater than the length of said curtain along lines spaced transversely of its center line, the greater length of said curtain along its longitudinal center line being c1jeated through the v provisiQm of a surplus ofniaterial adjacent to and intending away from the slit edge of the curtain where it is attached to x said strip.

2. A shutter curtain according to claim 1 wherein` the slit forming strip comprises a rod extending transversely of the curtain and having wrapped tlier'e'abdiittl'e leading edge of said curtain, said leading edge being arcuate inthe directionof its r'noveincnt during exposure operation, said slit forming strip also including an element extending transversely of the curtain and embracing said rod and those portions of the leading edge of the curtain adjacent to the rod, said arcuate curtainuedgebeing so disposed in relation to a straight edg of said le'nient as' to be substantially parallelthereto, whereby there is created a surplus 4of curtain niaterialadjacent said slit orniirig strip along the central portions thereof.

3. a fof' plane, shutter curtain, in conbinatiori a relatively rigid'straight slit Aforming strip, a 'cloth curtain nieinbr having slit and roller attaching edges, and means for attaching the slit edge o'f said curtain ineinbc to said strip, said roller attaching curtain edge being parallel to said strip, the length of said curtain While niotionl s being "g'reateialong its longitudinal center line than the length th curtain along lines spaced transversely of its center line whereby there are ,c ated loosefolds of curtain fabric between said slit and ille'r attaching edges.

IRVING W. DOYLE. CARL V. JOHNSON.

REFERENCES CITED rlhe following references are of record in the le of this patent:

UNITEl STATES PATENTS' Number. Name Date 504,425 Schramm Sept. 5, 1893 741,193 Br'sum oct. 13, 1903 .3u '792,361 Stocoum et al June 13, 1905 arraigo ruimer ;g l Feb. 5, 1907 2,133,011 Black Oct. 11, 1938 FOREIGN PATENTs ff Number. Country., Date 14,839 Great Britain 1893 308,592 Germany July l2, 1919

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