GB2244345A

GB2244345A - Supporting device of plastic lens

Info

Publication number: GB2244345A
Application number: GB9028116A
Authority: GB
Inventors: Hiroshi Nomura; Takayuki Ito
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1990-05-23
Filing date: 1990-12-28
Publication date: 1991-11-27
Anticipated expiration: 2010-12-28
Also published as: DE4042055A1; JPH0413909U; GB9028116D0; FR2662509A1; KR970003951Y1; FR2662509B1; GB2244345B; KR910020736U

Abstract

A supporting device for a circular plastic lens made of molded plastic and having had a sprue which was adapted to pour lens molding materials therethrough upon molding and which, having been mostly removed, remains as a gate portion projecting from the outer periphery of the plastic lens and a lens holder which supports therein the plastic lens. The lens holder has a recess in which the gate portion is fitted to restrict the angular position of the plastic lens. <IMAGE>

Description

- I--- -ISUPPORTING DEVICE FOR PLASTIC LENS The present invention relates

to the supporting mechanism for a plastic lens; more precisely, it relates to a camera having a plastic lens.

Upon molding a plastic lens, a sprue through which lens molding materials are poured remains as a gate portion projecting from the outer periphery of the circular lens. The gate portion is finally removed so that the product -the circular lens -- can be formed and finished, and then fitted in and held by a lens supporting frame. When the lens is assembled, however, no attention is paid to the location of the portion (which will be referred to as the near gate portion hereinafter) of the plastic lens that has the removed gate portion.

The reason this is important is that the near gate portion of the plastic lens tends to be somewhat distorted and, accordingly, even in products which are designed to have good quality lenses, particularly in terms of appearance, light which passes through the near gate portion tends to contain an aberration in comparison with light which passes through the other portion of th e lens.

As far as conventional camera lenses are concerned, the distort ion/aberrat ion of the near gate portion has not been focused on as a problem which should be solved and, accordingly, there remains the possibility that assembled plastic lenses may not be able to form high-quality images.

An object of the present invention is to provide a supporting device for a plastic lens in which possible aberration of the near gate portion can be taken into account.

-2 Another object of the present invention is to provide a camera lens in which possible aberration of the near gate portion can be effectively absorbed so as not to affect the quality of an image.

According to the present invention, there is provided a supporting device for a circular plastic lens made of molded plastic, the lens having had attached to it a sprue which was adapted to pour lens molding materials therethrough upon molding and which remains as a gate portion projecting from the outer periphery of the plastic lens, and also provided is a lens holder which supports therein the plastic lens; the improvement comprises a gate portion indicating means for indicating the position of the gate portion of the lens, and a positioning means on the lens holder for preventing the plastic lens from rotating with the help of the gate portion indicating means.

The gate portion indicating means can be constituted by the gate portion of the plastic lens itself, and the positioning means is comprised of a recess formed on the lens holder which is not rotatable, so that the gate portion can be made to remain engaged in the recess.

With this arrangement, since the position of the lens in the direction of rotation thereof is restricted by the positioning means, the aberration of the near gate portion can be taken into account.

To minimize the effect of the aberration of the near gate portion on a rectangular picture, it is desirable to place the gate portion so that it projects toward a major side of the rectangular picture frame in the view finder. Namely, the image formed by the camera lens, including a plastic lens, is basically circular and, accordingly, the influence of the aberration of the near gate portion which is located on the outer periphery of the plastic lens mainly appears in the vicinity of the outer periphery. Since the rectangular picture frame occupies a rectangular 3 part of the circular image corresponding thereto, if the gate portion extends toward the major sides of the rectangle, i.e. in a direction substantially parallel with the minor sides, no portion of the image on which the adverse ef f ect due to the 5 aberration is felt is taken in the picture frame.

It is possible to place the gate portion in a position other than in the above-mentioned position. With the present invention, the position of the plastic lens in the direction of rotation thereof about the optical axis is specified, so that the aberration can be taken into account to minimize the influence thereby. Consequently, it is the special intention of the designer that the aberration of the near gate portion should be positively utilized, the recess of the lens holder can be placed in a position other than the foregoing.

According to another aspect of the invention there is provided a camera comprising a plastic lens which constitutes at least a part of a camera lens and which has at its periphery a molding gate projection, and a non-rotatable lens holder which holds the plastic lens and which has a recess in which the gate projection of the plastic lens is fitted to restrict an angular position thereof.

According to a still further aspect of the invention there is provided a supporting d evice of a circular plastic lens made from molded plastic and having had a sprue which was adapted to pour lens molding materials plastic therethrough upon molding of the lens and which remains as a gate portion projecting from the outer periphery of the plastic lens and a lens holder which supports therein the plastic lens, wherein the improvement comprises a pair of male and female positioning means engageable with each other, provided on the plastic lens and the lens holder.

Conveniently said male positioning means is comprised of a projection formed on the plastic lens. Said female positioning means can be comprised of a recess formed on the lens holder, 4 so that the projection of the plastic lens can be fitted in the recess. Preferably said projection is formed by the gate portion of the plastic lens.

An example of the present invention will be described below in detail with reference to the accompanying drawings, in which:

Figure 1 is a front elevation view of the main part of a camera lens embodying the present invention; Figure 2 is a sectional view taken along the line II-II in Figure 1; Figure 3 is an exploded perspective view of a camera lens embodying the present invention.

A plastic lens 11 embodying the present invention has a gate portion lla which was formed by a sprue through which lens molding materials (monomer composite or molten polymer) was poured during molding. A lens holder (frame) 12 which simultaneously holds the plastic lens 11 and a glass lens 13 together has at its axial opposite ends holding portions 14 and 15. The first holding portion 14 for the plastic lens 11 has a circular opening 14a and a recess 14b which is formed on the peripheral edge of the circular opening 14a to outwardly extend in a radial direction. The gate portion lla of the plastic lens 11 is fitted in the recess 14b.

The second holding portion 15 for the glass lens 13 has a simple circular shape.

The lens holder 12 constitutes, for example, a variable power lens group of a zoom lens together with another lens group or other lens groups (not shown). The lens holder 12 has a linear guide surface 16 which lies in a plane parallel with the optical axis of the lens to be engaged by a linear guide member of a lens barrel (not shown). Namely, the lens holder 12 moves in the optical axis direction without rotating about the optical axis. That is, there is no change in the angular position of the lens holder 12 in the direction of the rotation thereof with respect to a rectangular (not square) picture frame of, for example, a 35 mm film. The recess 14b of the lens holder 12 extends toward the major side 20a of the rectangle (picture frame 20) in the radial direction of the opening 14a. Namely, the gate portion Ila of the plastic lens 11 does not project in a direction parallel with the major side 20a of the rectangle 20, when the gate portion Ila is fitted in the recess 14b. In other words, the gate portion Ila projects in a direction substantially in parallel with the minor sides 20b of the rectangle 20.

The plastic lens 11 is immovably secured to the lens holder 12 by a lens retaining ring 17 in a state that the gate portion Ila of the plastic lens 11 is fitted in the recess 14b of the lens holding portion 14. The immovable connection of the plastic lens 11 to the lens holder 12 is effected by the lens retaining ring 17 which has a securing -6 hole 17a in which a supporting projection 12a provided on the lens holder 12 is fitted and thermally fused in order to be joined. The glass lens 13 can be secured to the lens holder 12 by, for example, thermally calking a peripheral edge of the second holding portion 15.

In the camera lens as constructed above, even if there is an aberration due to distortion which remains in the vicinity of the gate portion lla of the plastic lens 11, in an image which is formed by the whole camera lens there is no possibility (or less possibility) that the image having the aberration will be taken in the picture frame 20. This is because the image with the aberration is located around the generally circular image, so that the major sides 20a of the rectangular picture frame 20 cuts the formed image 15 in a correspondingly rectangular shape so as not to take an image of the circumferential portion having the aberration due to the existence of the gate portion lla.

This technical advantage can be made clearer in comparison with an arrangement in which the gate portion lla projects toward the minor sides 20b of the rectangular picture frame 20. In such an arrangement, a broader range of image from the center of the plastic lens 11, that is, the portion having the aberration due to the gate portion lla or the vicinity thereof is taken in the picture frame 20.

Claims

CLAIMS:

I. A supporting device for a circular plastic lens made of molded plastic and having had a sprue which was adapted to pour lens molding materials therethrough upon molding and which remains as a gate portion projecting from the outer periphery of the plastic lens, and a lens holder which supports therein the plastic lens, wherein the improvement comprises; a gate portion indicating means for indicating the position of the gate portion; and, a positioning means on the lens holder for preventing the plastic lens from rotating with the help of the gate portion indicating means.
2. A supporting device according to claim 1. wherein said gate portion indicating means is formed by the gate portion remaining on the plastic lens.
3. A supporting device according to claim 2, wherein said positioning means is comprised of a recess in which the gate portion is fitted.
4. A supporting device according to claim 3, wherein said lens holder is not rotatable.
5. A supporting device according to claim 4, wherein said recess of the lens holder is located so that the gate portions fitted in the recess projects toward a major side of a rectangular picture frame.
6. A camera including a supporting device as claimed in any preceding claim.
7. A method of constructing a plastic lens arrangement comprising the steps of:molding a plastic lens by pouring lens molding material into a mold through a sprue portion, the said sprue portion remaining as a gate portion projecting from the outer periphery of the molded plastic lens; and 8 mounting the plastic lens in a lens supporting means having cooperating means for cooperating with the gate portion to mount the lens in a predetermined angular position and to prevent rotation thereof.
8. A supporting means for supporting a plastic lens molded by pouring plastics material into a mold through a sprue portion, the said sprue portion remaining as a gate portion projecting from the outer periphery of the molded plastic lens, the supporting means having cooperating means for cooperating in use with said gate portion to mount the lens in a predetermined angular position and to prevent rotation thereof.
9. A supporting device f or a circular plastic lens made of molded plastic and having had a sprue which was adapted to pour lens molding materials therethrough upon molding and which remains as a gate portion projection form the outer periphery of the plastic lens substantially as herein described with reference to the accompanying drawings.

Published 1991 at The Patent Office. Concept House, Cardiff Road, Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwrnfelinfach. Cross Keys, Newport. NP I 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent,