US2508371A - Reticle - Google Patents

Description

ca 295080371 5R Patented May 23, 1950 o EHHUITTITW OFFICE RETICLE James M. Brady, Washington, D. 0., and Samuel Posten, Navesink, N. J.

No Drawing. Application February 12, 1946, Serial No. 647,182

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 57)

1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to reticles for various optical instruments, such as range finders, bombsights, telescopes, gunsights, submarine periscopes, etc.

Jacobs, in his book entitled Fundamentals of Optical Engineering, 1943, states that the subject of reticles appears very simple; actually, it

is very complex, and much research has been and is being done in this field. The dificulty in securing a satisfactory reticle is shown by the fact that spider threads, or spider silk, are still used, notwithstanding extended efforts to secure more satisfactory material. Spider threads are objectionable for a number of reasons. They are hygroscopic, and lengthen when they absorb moisture, which results in a sagging that renders the reticle useless. The instrument involved must then be sent for repairing, with consequent temporary loss of use of same. They must also be delicately handled and must be wound on frames for transportation and storage, and are difficult to disentangle for use. They further involve an operation for removing dust particles. Finally, considerable care and skill are required in mounting them, which operation must be done with precision, including the proper degree of tension on the threads.

Platinum and tungsten wires have been tried, but these are expensive to produce, due to the great fineness required, this being of the order of one ten-thousandth of an inch. To draw a metallic wire of such fineness requires that the metal to be drawn for use be ensheathed in another metal, the two then being drawn until the ,inner wire is of the required diameter, great care and accuracy of dies being needed towards the end of the drawing operation. It is then necessary to dissolve the sheathing metal. To produce, by this process, wire fine enough for use under very high power eyepieces is very diflicult and expensive.

Lines ruled on a thin plate of glass have also been tried, but this results in a loss of light in the field of view due to absorption of light by the glass, which is increased when dust and a moisture film collect on it and fog the image. Further, the ruled lines must be coated with an opaque material to render them visible. Many photographic techniques have also been developed for the purpose, but these are expensive and many difliculties are encountered and various precautions must be taken.

It is therefore an object of this invention to provide reticles which are free from the objections mentioned and which have advantages not possessed by those of the prior art.

It will be shown that reticles which may be produced according to this invention are very economical, have lines of any desired degree of fineness, which may be finer than any heretofore reproduced, may be quickly and accurately formed, are non-hygroscopic, may be and preferably are mounted under ,tension, to guard against any possible sagging; are self-afllxing, that is, need no adhesive to secure them to the supports or frames, are not brittle, and have other advantages. Among the latter is the luminescent property imparted to them when a. suitable material, as a fluorescent dye, for example, is incorporated in the composition from which the reticles are made, said composition being in such form, as hereinafter disclosed,-

that the luminescent material may be readily admixed therewith. The luminescence of the reticles made in accordance with our invention enables instruments employing them to be used in the dark without interference from annoying light which otherwise must be used to render the reticle visible.

A still further valuable feature of our invention is due to the self-affixing quality, which may be used when desirable, whereby crossing or intersecting lines or threads may be secured to each other without the use of any adhesive, which would intolerably enlarge the point of intersection, as viewed under a high power eyepiece. The mentioned self-aflixing property is valuable not only for the reason just stated, but because the lines being joined at the intersections, the outer ends thereof may be shifted, one at a time and with the other ends secured to the frame, so that any desired configuration, as a Y formation, for example, may readily be made, which will be readily understood by those skilled in the art.

Having consideration of the fact that the principal obstacle to be overcome, in providing improved reticles, is that of finding a composition which may be readily drawn into threads sufficiently fine, we have found that viscous solutions may be quickly drawn out manually into threads which may be as fine as desired, said solution comprising a solvent which is vaporizable after the thread is drawn. The solvent is preferably a volatile liquid which more or less quickly vaporizes at room temperature, to eliminate the necessity of performing the additional operation of separating it from the solute. The latter may be any suitable solid material having adequate tensile strength, as shown by known data for such property, and the viscosity of the solution, which is not critical, may have any convenient or practical value permitting the ready drawing into threads or lines.

If rubber, or a rubberlike or elastoliierio moterial is used as the solute, added advantages are gained over some of the other materials which are adequate, such as the non-hygroscopic synthetic high polymer, for example, and other organic solids having sufiiciently high tensile strength and elasticity. The elastomers of this class, due to their elasticity, permit the reticles to be mounted under tension to prevent any possible sag. Further, such material is non-hygroscopic to a high degree. The elastomeric material may be either from a natural source or may be synthetic. As an example, polychloroprene, commonly sold under the trade-mark Neoprene, may be dissolved in toluene to make a thick or viscous solution which on test is stringy. Any suitable phosphor, preferably a dye, may be incorporated if it is desired to make the reticle luminescent. The dye, or other phosphor, should not be admixed as a powder, as the particles thereof, or some of them, may be of such size as to disadvantageously affect the quality of the thread or the uniformity of its diameter, which will be readily appreciated when it is remembered that the thread has a diameter of only about one ten thousandth of an inch. The dye should therefore be introduced in the form of a solution, using a volatile solvent. These dyes, and solvents therefor, are known, and need not be stated here for that reason. A small portion of the mass of the viscous solution is withdrawn from the batch and pulled out manually to the required fineness. The threads or lines so formed are adhesive before the volatile solvent evaporates, so that they may be attached to the frame without use of the usual shellac or other adhesive. For the same reason, crossing threads may be secured together at their intersection merely by bringing them into contact, the strength of the reticle being thereby lncreased- As pointed out above, this adhesive property is an important advantage, as any added adhesive would objectionably enlarge the point or points of intersection. It is desired to call attention to the fact stated above, viz., that the fixation of crossing threads allows reticles of special formation to be readily made in the manner explained. If, however, it is not desired to utilize the property of adhesiveness, it is only necessary to lay the thread aside for a short time after drawing it, until all of the volatile solvent has evaporated.

In the making of reticles by application of spider silk to the supporting frame, the technique developed comprises the use of a divider, to the points of which small masses of an adhesive, as shellac, are applied. The silk or thread is attached to one of the adhesive masses and then pulled carefully, at the proper tension, to

;he other mass, and attached thereto, the length of silk being necessarily comparatively short. The thread is then laid precisely on the line intended, and is secured to the frame at two points by placing adhesive on the thread and on the frame. As stated above, the length of silk carried on the dividers is comparatively short, otherwise, with the silk of considerably greater length, the preolnon ottomoblo would be less than that possible by using a comparatively short length. Employing our invention, however, each thread may be quickly secured to the frame with accuracy, and without using a divider or other instrument, by having a comparatively long thread, which may advantageously be about two feet long, attaching this to on point on the frame without the necessity for using an adhesive, the viscous thread being itself adhesive, and then manually moving the other end of the thread until that part of the thread which is over the frame is in the proper position, whereupon the thread is brought down to make the second point of contact with the frame, the excess length of the thread being cut off. The advantage in using a thread of the length stated will be evident when it is considered that, in moving the thread for proper positioning before making the second point of attachment, a comparatively large arcuate movement of the hand may be made for a small movement of the thread over the frame.

What is claimed is:

A ret-icle comprising a frame to which are rigidly secured a plurality of crossed, self-affixing filar cross-hairs which are held under tension in nonsagging relation, said cross-hairs being formed of polychlgrgpren and being secured to said frame and to each other at their point of intersection solely by reason of the inherent adhesive quality thereof, and being substantially unaffected by normal changes in humidity and temperature of th ambient air.

JAMES M. BRADY. SAMUEL POSTEN.

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

UNITED STATES PATENTS Number Name Date 692,467 Mugnier Feb. 4, 1902 1,529,643 Fenderl Mar. 10, 1925 2,243,793 Cummins May 27, 1941 2,245,310 Waterman et a1. June 10, 1941 2,270,307 Karnes Jan. 20, 1942 2,401,015 Perkins May 28, 1946 FOREIGN PATENTS Number Country Date 17,549 Great Britain of 1898 OTHER REFERENCES Jacobs: Fundamentals of Opt. Eng, McGraw- Hill, N. Y., 1943, page 202.

Foster: Simplified preparation of microscope cross hairs, Science. vol. 84, No. 2187, Nov. 2'7, 1936, page 490.