Technical Field

This invention relates to a lens mounting for enabling rapid changes of lenses.

Background Art

In the field of optical systems wherein a lens is utilized for magnifying certain information, it is important that the lens be positioned and maintained in such position to provide proper focusing for reading the information. In the case of a projection-type lens, it is advisable to use a high-efficiency lamp along with a high-resolution lens to obtain optimum operating conditions.

Since proper focusing of the optical system is extremely important, various ways and means have been utilized for moving the lens along the axial direction in relation to an optical plane. One well-known method is to adjust the position of the lens along its optical axis by camming means which includes structure whereby the lens and the barrel are axially moved in relation to the optical or focal plane. Another method may use bevel surfaces in the nature of a helical curve whereby a pin or like member is caused to be moved along the curve for adjusting the lens in a manner to provide proper focusing thereof. In a number of these systems it is usually required to re-focus the lens system upon reading of different information on microfilm or the like when such film is caused to be replaced in film viewing apparatus. Additionally, an optical lens may be positioned and retained in a system which includes structure for securing the lens in a manner to avoid repeated re-focus¬ ing of the lens and such structure may be designed to make fast and simple changing of the lens which is then in the apparatus for a lens of a different magnification.

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In the case of a viewer or reader for accom¬ modating microfilm or microfiche it is well-known that the reduction ratio of such microform readers may vary, for example, from 24 to 150 times and also the ratio of the microfilm may vary. Because of these variations, it becomes advisable to have available a number of lenses of different magnification values rather than a plural¬ ity of readers with different reduction ratios.

The use of different magnification lenses in a specific reader or like apparatus presents a problem of maintaining focus when the lenses are interchanged to accommodate a microform or microfilm of like ratio. Ad¬ ditionally, it becomes necessary to provide structure which enables changing or replacing lenses in the short- est possible time.

Representative prior art of lens mounting in¬ cludes United States Patent No. 2,469,781 which discloses a lens carrying structure which is detachably secured to an apertured support structure. The lens carrying structure is provided at one end with an externally threaded cylindrical flange for manually threading or unthreading the lens carrying structure respectively into or out of an inwardly threaded annular portion of the support structure. While this arrangement enables the easy changing of lenses of different focal dis¬ tances, the threading and unthreading operations are somewhat time consuming.

Bayonet type lens mounting systems, such as those used for the lens mountings of many photographic cameras enable much more rapid changing of lenses. How¬ ever, the structure of such mountings requires intricate machining to hold the lens against a defined surface.

Disclosure of the Invention

It is an object of the present invention to provide a lens mounting which includes structure for securing a lens in a manner to avoid repeated re-focusing

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of the lens and which enables fast and simple changing of lenses without the disadvantage associated with the requirement for precision machining of parts of the structure. Thus, according to the invention, there is provided a lens mounting for enabling rapid changes of lenses, wherein a lens carrying structure is arranged to be detachably secured to an apertured support struc¬ ture, characterized by a one-piece spring element which is secured to a first one of the two structures and which has an aperture through which passes the opti¬ cal axis of said lens carrying structure when the two structures are secured together, the two structures being arranged to be secured together by virtue of lugs provided on the second structure engaging between said spring element and a rigid portion or portions of said first one of the two structures, whereby said spring element biases said lugs against said rigid portion or portions, said lugs being releasable from engagement by said spring element and said rigid portion or portions by bringing about relative rotational movement between said lugs and said rigid portion or portions.

Brief Description of the Drawings

Several embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a lens being changed in appropriate microform handling apparatus;

Fig. 2 is an enlarged side view showing one embodiment of the lens mounting according to the inven¬ tion;

Fig. 3 is an exploded view showing several parts of the lens mounting of Fig. 2;

Fig. 4 is a side view showing another e bodi- ment of the lens mounting according to the invention; and

Fig. 5 is a detail view of a spring element shown in Fig. 4.

Best Mode of Carrying Out the Invention

Referring to Figs. 1, 2 and 3 of the drawing, a frame member 10 is provided with a side portion 12 and a top portion 14, the top portion having an opening 16 therein for receiving a lens carrying structure or assembly 18 shown in position to be installed in an aper- tured support structure for subsequent operation. A lens cube 20 is supported from a cradle 22 and is provided with a protective cover 24. An enlarged view of the several parts of the lens mount shown in the exploded view of Fig. 3 includes the top portion 14 of a reference plate 25 and the aperture 16 in a plate portion 26. The plate portion 26, also seen in Fig. 2, is formed adjacent a base plate 27 and the reference member 25 to provide a recess 28 for receipt of a female bayonet plate 30 and a one-piece, planar, spring element 32. Tapped holes 36 are provided in the bayonet plate 30 and also apertures 38 in- the clamping spring 32 for receipt of screws 40 to secure the spring 32 to the bayonet plate 30. The plate 30 is positioned in abutting manner with the central portion 34 of the reference plate 25. A pin 31 is provided in the plate 25 on opposite sides of the aperture 16 to match a hole and a slot in the plate 30. A cover plate 33 with an opening 35 therein is secured by screws 37 in tapped holes 39 of the reference plate 25.

The lens assembly 18 comprises a lens holder 42 (Fig. 2) adapted to enclose and retain a particular lens of a stated magnification (42X) and has threads 44 on a peripheral portion thereof for engaging with threads 46 on an interior diameter of a male set bay¬ onet 48. The male bayonet 48 is provided with screw means 49 or the like for tightening adjacent portions thereof so as to precisely position and retain the lens holder 42 in relation to the bayonet 48. In this man¬ ner, the lens is set for proper focus relative to a

microimage plane 47 above the lens assembly 18 and, when the critical focus is established and set, the focus condition will remain until the lens is removed from the holder 42. The male bayonet 48 has three lugs or tabs 50

(Fig. 3) at the upper end thereof, equally spaced and extending outwardly to engage with the female bayonet plate 30 and against the clamping spring 32. The bayonet plate 30 is seated in the recess 28 of the stepped portion of reference plate 25 and, with the spring 32 secured to the plate 30 and retained by the cover plate 33, the lugs or tabs 50 are held in place by the respective planar surfaces of the several parts. The cover plate 33 has four gaskets or pads 51 to provide clearance for the screws 40 and also to enable adjustment at the several corners of the plate 33. The diameter of the aperture 16 in the plate portion 26 and the diameter of the aperture 52 in the bayonet plate 30 enable the male bayonet 48 wit its lugs 50 to pass through the apertures with the apertures having clearance diameters. The plate 30 includes lugs or tabs 54 and the spring 32 includes a central aperture 55 having a diameter approximately the diameter of the internal threaded portion of the male bayonet 48 so as to pro- vide a seat for the lugs or tabs 50 of the male bayonet 48 within the gap between the plate lugs 54 and an interior portion 56 adjacent the aperture 55 of the spring 32, and defined by the offset 57 of the lugs 54 from the upper surface of the plate 30. Each of the male bayonet lugs 50 has an inclined or slanted surface of fifteen degrees, as shown by the arrow 58, on the underside at one edge of each lug so as to enable ease of engagement in the gap between the lugs 54 and the portion 56 of spring 32 when the lens assembly 18 is being installed by turning in a clockwise direction as seen in Fig. 1. One of the lugs 54 of the plate 30 has a stop pin 60 for limiting the extent of travel of the male bayonet 48.

Fig. 4 shows another form of the lens mount wherein a lens assembly 62 includes a lens holder 64 adapted to enclose and retain a particular lens (not shown) of a stated magnification and has threads on a peripheral portion for engaging with threads on an interior diameter of a male bayonet 66, which is pro¬ vided with means 68 in the form of a screw for tighten¬ ing adjacent portions of the bayonet so as to precisely position and retain the lens holder 64 in relation to the bayonet 66, all in a manner similar to that shown in Fig. 2. In similar manner as described above, the lens is set for proper focus relative to a microimage plane 69 above the lens assembly 62 and, when the cri¬ tical focus is established and set, the focus condi- tion will remain until the lens is removed from the holder 64. The bayonet 66 also has three equally- spaced lugs or tabs 70 extending outwardly to engage with corresponding lugs or tabs 72 of a lens clamping spring 74 of the shape as seen in Fig. 5. The spring 74 is supported against and along with a lens mounting ring 76 to the underside of a supporting plate 78 by means of screws 80. The plate 78 has an aperture 82 for passage of projected light therethrough to the plane 69 and a larger aperture 84 for seating of a beveled portion 86 of the bayonet 66. A stop pin 88 is also provided at one edge of one of the tabs 72 of the mounting ring 74 (Fig. 5).

In the preferred embodiment of the present invention, shown in Figs. 1, 2 and 3, the lugs or tabs 50 have a beveled entry angle of fifteen degrees and have a thickness of 2.41 millimeters for fitting in a gap of 2.16 millimeters provided between the lugs 54 of the female bayonet plate 30 and the resilient portion 56 of the spring 32. When the male bayonet 48 is turned to engage the tabs or lugs 50 thereof with the lugs 54 of female bayonet plate 30, the interference fit of 0.25 millimeters requires the portion 56 of spring 32 to

push or bias the lugs 50 of the lens carrying structure 18 downwards against the lugs 54 of the bayonet plate 30. The spring 32 is calculated to provide a minimum of 4.5 kilograms of clamping force with the 0.25 milli- meters interference fit. The resilient portion 56 adjacent the aperture 55 of the spring 32 is of at least sufficient distance from the aperture to cover the lugs 54 in overlapping manner. In other words, the resilient portion 56 extends at least from the aperture 55, which may be approximately the diameter of the interior edge of the lugs 54, to an imaginary circle, as shown by the phantom line on the clamping member 32 of Fig. 3, the imaginary circle being approximately the diameter 52 of the plate member 30. It is, of course, feasible and may be preferred that the clamping member be made entirely of resilient material of the same composition.

In similar manner, the interference fit of the tabs 70 on the male bayonet 66 in the modified form of the invention (Figs. 4 and 5) enables the spring 74 to push or bias the lugs of the lens carrying structure 62 upwards against the plate 78.

The bayonet-mounted lens holder is a preci¬ sion device in that controlled spring pressure main¬ tains the lens assembly against a reference surface for repeatable positioning of the lens assembly in pre¬ cise manner. When the lens assembly is mounted against the reference plate and a set of different magnifica¬ tion ratio lenses are properly focused, the lenses of the set can be exchanged or replaced in a few seconds by reason of the quick change lens mounting assembly. In operation, it is thus seen that in the preferred structure when one lens is to be changed or replaced, for example, for another lens of a different magnification, the lens assembly 18 is positioned with- in the apparatus utilizing such lens assembly, as seen in Fig. 1, and upon moving the lugs 50 of the bayonet 48 up into the plane of the gap 57 between the lugs 54

of the bayonet plate 30 and the resilient portion 56 of the clamping spring 32, the lens assembly 18 is rotated by hand about 35 degrees to engage the respective lugs and to seat one lug 50 against the stop pin 60 and thereby precisely position the lens in relation to the plane 47. When so positioning the lens assembly 18, the clamping spring 32 biases or urges the bayonet 48 in a downwardly direction to firmly press the lugs 50 against the lugs 54 of the plate 30. In similar manner in the modified structure, when one lens is to be changed for another lens, the lens assembly 62 is positioned within the apparatus and upon moving the lugs 70 of the bayonet 66 up into the plane of the gap between the lower surface of the sup- porting plate 78 and the resilient portions 72 of the lens clamping spring 74, the lens assembly 62 is rotated by hand about 35 degrees to engage the respective lugs and to seat one lug 70 against the stop pin 88 and thereby precisely position the lens in relation to the plane 69. When so positioning the lens assembly 62, the lens clamping spring 74 biases or urges the bayonet 66 in an upwardly direction to firmly press the lugs 70 against the lower surface of the plate 78.

Additionally, while the bayonet 48 of the lens assembly 18 has lugs 50 attached thereto for cooperating with the lugs 54 of plate 30 and the resil¬ ient portion 56 of clamping spring 32, such lugs 50 may be a part of a portion attached to an apertured support member and the member 30 may be a part of the bayonet 48 and cooperable with the clamping spring 32. In this manner a plate member and a planar spring having cooper¬ ating portions thereon similar to lugs 54 of member 30 and the resilient portion 56 of spring 32 could be secured to the lens carrying member and the support member could carry lugs similar to lugs 50 for the purpose of precisely positioning the lens carrying member. The support member could have the lugs down-

wardly positioned and extending outwardly in a plane perpendicular from the axis of the aperture in the support member and when the lens assembly with the plate member and the planar spring attached thereto are positioned to receive the lugs of the support member, the spring would bias or urge the lugs of the support member in the space between the resilient portion of the spring and the lugs of the plate member. It should be noted that both the spring and the plate member would require access portions on the interior diame¬ ters to allow passage of the outwardly extending lugs of the support member and then include inwardly ex¬ tending tabs, similar to tabs 54 shown in Fig. 3, to provide the seat therebetween for the lugs of the sup- port member.

A further modification of the clamping or resilient member may include a larger internal diame¬ ter than is shown in Fig. 3 and having a plurality of resilient portions angularly corresponding with the lugs 54 of the bayonet plate 30 to thereby enable passage of the member 48 with lugs 50 through the apertures and to place the lugs 50 between the resili¬ ent portions of the clamping member and the lugs 54. In the practice of such modification, the lugs 50 may require a beveled portion on each end thereof to pro¬ perly engage in the space between the portions of the clamping spring and the tabs of the bayonet plate member. Additionally, the resilient portions may be separated only by a kerf provided to form a plurality of resilient portions at least in sufficient diame¬ tral distance to cover the lugs of the member 50 and the tabs of the plate member 30.