GB2187863A - Lens holder - Google Patents

Abstract

A lens sleeve (2) is guided in a guide frame (7) of a lens holder (1) at three points by means of guide projections (17, 18, 19 or 17b, 18b, 19b). In each case, two guide projections (17, 18, 17b, 18b) are fixed whilst the other guide projection (19, 19b) is able to spring radially with respect to the lens sleeve (2) and presses the latter against the other guide projections (17, 18, 17b, 18b), in order to permit clearance-free guidance. The movable guide projection may be biased by a spring in the direction of the lens sleeve (Fig. 3). The holder may be used in a microfilm reader. <IMAGE>

Description

SPECIFICATION Lens holder This invention relates to lens holders for lens sleeves and is particularly concerned with a lens holder for a lens sleeve which is arranged in floating manner, can be supported on a film stage and secures a lens in vertically adjustable manner, the lens sleeve being held in a vertically displaceable and rocking manner in a guide. Such a lens holder is described, for example in DE-AS 2041335.

In the case of lens holders with a floating lens sleeve, it is necessary for the latter always to be at right angles to the upper plate of the film stage. For this purpose it must not only be movable up and down in its guide, but must also be able to perform a universal tumbling movement. In addition, the lens sleeve position must be very precisely fixed, so that in the case of the automatic moving along of an image, the latter is fully projected by the lens onto a ground glass screen. Even minor positional variations of the lens lead to marked displacements of the image on the ground glass screen, due to the high magnification factor occurring with microfilm readers.

This neeed for precise positioning reguires an optimum clearance-free guidance of the lens sleeve. However, the guidance of the lens sleeve must be as smooth as possible, so that it can adapt to the course of the upper plate of the film stage.

In the lens holder according to DE-AS 2041335, an attempt was made to satisfy this requirement by using an elastic ring, which is arranged in such a way in an allround groove of a guide sleeve receiving the lens sleeve that it firmly engages against both the guide sleeve and lens sleeve. Tumbling of the lens sleeve is then possible through the deformation of the elastic ring. However, it is a disadvantage of such a ring that as a result of its radial force directed against the lens sleeve, a displacement of the latter is made much more difficult. In the known microfilm reader an attempt is made to compensate this through the use of springs, which press from above on the lens sleeve and keep the latter in constant contact with the film stage.However, this measure leads to considerable expenditure and causes high friction between the lens sleeve and the upper plate of the film stage, which leads to drive problems in the case of a motor-movable film stage.

It is already known from German patent Application F 34 39 254.8 to provide the lens sleeve with an external, all-round bead, which in a guide sleeve of the lens holder engages with limited clearance against the inner circumferential surface of said guide sleeve. However, even this lens holder fails to fulfil all of the requirements made thereon. If the desired easy motion of the lens sleeve is achieved, this leads to a guide clearance preventing exact positioning of the lens relative to the individual images which are automatically moved along. In particular, there is a reversal clearance as a function of the direction from which a desired film image is moved in.A further disadvantage is that in the case of automatic film stage movement, such a lens sleeve leads to fluttering as a result of its clearance, because the film stage is moved with stepping motors, which lead to a jerky movement thereof. This leads to undesired jittering of the image on the ground glass screen and also to disturbing chattering and rattling noises.

The present invention aims to provide a lens holder having a simple construction, whose lens sleeve supported on a film stage can be pivoted and moved vertically very smoothly, but which is held in clearance-free manner, so as to bring about precise position fixing and prevent rattling of the lens sleeve in the case of a motor traverse of the film stage.

According to the invention, there is provided a lens holder having a guide for supporting a lens sleeve in a vertically displaceable and rocking manner, wherein the guide comprises two fixed guide projections and a movable guide projection which is arranged to be urged in a resilient manner radially with respect to the lens sleeve against the latter to press the same against the fixed guide projections.

In the case of such a construction, the lens sleeve only engages against the guide projections of the lens holder at three points. As the contact areas can be made small, limited frictional forces result. The movable guide projection presses the lens sleeve continuously against the two fixed guide projections, so that the position of the lens holder is necessarily precisely fixed and there can be no rattling noises or jittering of the image. The clearancefree fixing of the lens sleeve also ensures that the lens is always precisely located on the optical axis of the individual film images. The easy motion of the guide in most cases renders superfluous pressure springs which downwardly bias the lens sleeve.Despite these functional advantages compared with known lens holders, the lens holder according to the invention has a very simple construction and is therefore inexpensive to manufacture.

As the radial forces acting on the lens sleeve and corresponding to the displacement directions of the film stage can come from four different directions, it is advantageous for the uniform supporting of all forces if according to a preferred embodiment of the invention the guide projections are spaced apart at an angle of 1200 to one another.

Preferably, the fixed guide projections and the movable guide projection are provided on a guide frame which is immovably secured to the body of the lens holder.

An adequateiy large spring travel in the case of the sought relatively small, radial forces can easily be achieved with respect to the movable guide projection, if the projection is located close to a free end of a resilient web of the guide frame and if said web extends externally past the lens sleeve from a fixing point of the guide frame to the lens holder body and is otherwise not connected therewith.

To prevent over extension of the web with the movable guide projection on inserting the lens sleeve, it is advantageous to limit the displacement of the web by a nose projecting away from the lens sleeve between two stops provided on the lens holder body.

Alternatively or in addition, the free end of the web may be biased by a spring in the direction of the lens sleeve. In the case of such a construction there is no dependency on the elasticity characteristics of the material forming the guide frame for producing the forces tensioning the lens sleeve.

It is advantageous from the manufacturing standpoint if the guide frame comprises two identical, homologous frame halves, so that there is then no need to manufacture and keep available two separate components.

Limited friction forces occur if the guide frame is made from plastics material. In addition, such a plastic part can be inexpensively manufactured as an injection moulding.

The invention will now be further described, by way of example, with reference to the drawings, in which: Fig. 1 is a side view of one embodiment of a lens holder according to the invention; Fig. 2 is a plan view, to a larger scale than Fig. 1, of part of the lens holder shown in Fig.

1; and Fig. 3 is a plan view of part of a second embodiment of a lens holder according to the invention.

Reference will f irst be made to Fig. 1 of the drawings in which the body of a lens holder 1 secures a lens sleeve 2. The lower end face of the lens holder is supported on an upper plate 3 of a film stage 4. The lens sleeve 2 is provided with a servomotor 5, which permits the focusing of a lens (not shown) which is displaceably guided in the lens sleeve. On the side of the lens sleeve 2 remote from the servomotor 5 is provided a counterweight 6, which compensates the tilting moment occurring as a result of the weight of servomotor 5 acting on one side of the lens sleeve 2. The basic principle of such a floating lens sleeve is described in detail in German Patent Application No. P 34 39 254 8.

Fig. 1 shows three upwardly directed tongues 8, 9, 10 on the lens holder 1 as well as a guide frame 7 for guiding the lens sleeve 2 and whose precise design can be seen in Fig.

2. The guide frame 7 comprises two identical, homologous frame halves 11 and 12 which are in each case fixed by means of two crossslotted screws 13, 14 and 15, 16 respectively to the lens holder 1. In the embodiment illustrated in the drawings, the lens holder 1 and the guide frame 7 are constructed for receiving two lenses guided in respective lens sleeves 2. However, Fig. 2 shows only one lens sleeve 2. It can be seen that the lens sleeve 2 engages against three guide projections 17, 18, 19 of the guide frame 7 which are at an angle of 1200 to one another, the guide projection 17 being covered by the counterweight 6. The guide projection 17 or the corresponding guide projection 1 7b shown in the lower part of Fig. 2 is precisely arranged and therefore fixed between the crossslotted screws 15, 16 or 13, 14.The guide projection 18 or 18b is also fixed, because it is located precisely in front of a cross-slotted screw 14 or 16. However, the guide projections 19 or 19b can spring radially with respect to the respective lens sleeve 2 and press the latter against the fixed guide projections 17 and 18 or 17b and 18b. For this purpose, the guide projections 19 and 19b are provided approximately at the free end of a web 20 or 20b extending in each case from a crossslotted screw 14 or 16 along the lens sleeve 2 and is connected to the lens holder 1 by the particular screw 14 or 16.

In order to facilitate insertion of the lens sleeve 2 into the guide frame 7 and to keep small the bearing faces of the guide projections 17, 18, 19 and 17b, 18b, 19b, the front ends thereof can be bevelled, i.e. widen conically upwards, (not shown). At the free end of each web 20, 20b is provided an outwardly directed nose 21, 21b which engages with clearance between the tongues 9, 10 or 9b, 10b. The webs 20, 20b and the resilient guide projections 19, 19b are only to a limited extent elastic.

The embodiment shown in Fig. 3 differs from the previously described embodiment in that the web 20b is biased at its free end in the direction of a lens sleeve 2b by means of a spring 22. Thus, the guide projection 1 9b is maintained not only as a result of the residual stress of the web 20b, but also through the tension of spring 22, against the lens sleeve 2b. The spring 22 is fixed between an extension 23 of the web 20 and a shoulder 24, which in precisely the same way as the nose 21b in Fig. 2 engages between tongues 9b and 10b. The other side of the frame halves 11, 12, not shown in Fig. 3, is also constructed with a similar spring.

Claims (9)

1. A lens holder having a guide for supporting a lens sleeve in a vertically displaceable and rocking manner, wherein the guide comprises two fixed guide projections and a movable guide projection which is arranged to be urged in a resilient manner radially with respect to the lens sleeve against the latter to prss the same against the fixed guide projections.

2. A lens holder according to claim 1, wherein the guide projections are spaced apart at an angle of 1200 to one another.

3. A lens holder according to claim 1 or claim 2, wherein the fixed guide projections and the movable guide projection are provided on a guide frame which is immovably secured to the body of the lens holder.

4. A lens holder according to claim 3, wherein the movable guide projection is located close to a free end of a resilient web of the guide frame, said web extending externally past the lens sleeve from a fixing point of the guide frame to the lens holder body and other wise not being connected to said lens holder body.

5. A lens holder according to claim 4, wherein the web is secured so as to be displaceable to a limited extent between two stops provided on the lens holder body by a nose extending in a direction away from the lens sleeve.

6. A lens holder according to claim 4 or claim 5, wherein the free end of the web is biased by a spring in the direction of the lens sleeve.

7. A lens holder according to any one of claims 3 to 6, wherein the guide frame comprises two identical, homologous frame halves.

8. A lens holder according to any one of claims 3 to 7, wherein the guide frame is made from plastics material.

9. A lens holder substantially as described herein with reference to the drawings.