WO1991009340A1

WO1991009340A1 - A lens attachment

Info

Publication number: WO1991009340A1
Application number: PCT/GB1990/001898
Authority: WO
Inventors: John Ernest Houghton
Original assignee: John Ernest Houghton
Priority date: 1989-12-07
Filing date: 1990-12-06
Publication date: 1991-06-27
Also published as: EP0457881A1; JPH04503873A

Abstract

A meniscus lens (1) comprises a partially reflective coating on one face which reflects a portion of incident light and transmits the remainder adapted, in use, to be attached co-axially in front of the lens of a camera with the rear concave surface thereof facing the camera lens such that the subject of a photograph, when looking towards the camera, sees reflected in the meniscus lens an image which is in all essential respects identical to the image which would be seen in the camera view finder.

Description

DESCRIPTION

A LENS ATTACHMENT

The present invention relates to a lens attachment and more particularly to a lens attachment which facilitates the taking of self portraits with a still, movie or video camera. When taking self portraits using any existing type of camera the photographer is unable to look through the camera view finder to see the image he is about to take. Though mirrors can be set up to the rear and sides of the camera, the composition and character of the photographs taken tend therefore to be rather uncertain.

It is an object of the present invention to provide a lens attachment whereby the image which would be seen in the camera view finder can be seen from in front of the camera. According to the present invention there is provided a meniscus lens comprising a partially reflective coating on one face which reflects a portion of incident light and transmits the remainder and which is adapted, in use, to be attached co-axially in front of the lens of a camera with the rear concave surface thereof facing the camera lens.

The subject of the photograph, when looking towards the camera, sees reflected in the meniscus lens an image which is in all essential respects identical to the image which would be seen in the camera view finder. Thus, the

SUBSTITUTESH meniscus lens of the present invention is particularly suitable for the taking of self portraits, though of course it also enables a subject to compose him or herself for a photographer. The partially reflective coating may be applied to either the front or the rear surface of the meniscus lens.

Conveniently, the partially reflective coating reflects approximately 50 of the incident light. This affords a clearly reflected image from the front of the camera, whilst still transmitting sufficient light to ensure that there is little effect on the image forming qualities of the camera lens. Any effect can be minimised by increasing the exposure time. The meniscus lens may be of zero power so that it does not have any significant effect on the optical characteristics of the camera lens. However, it may be convenient for the meniscus lens to be of finite converging power so that it then acts as a supplementary close up lens.

Advantageously, a mask is mounted on or immediately adjacent to the front convex surface of the meniscus lens so that the reflected image viewed from the front of the camera has essentially the same boundaries as the image which would be seen in the camera view finder.

Preferably, the meniscus lens attachment comprises attachment means whereby it can be secured to a camera. The attachment means may be such that in use the meniscus

SUBSTITUTE SHEET lens can be secured directly to the camera lens surround.

In this respect, the attachment means used may be of the types commonly used with photographic filters. However, as an alternative for use with cameras which do not make provision for the attachment of filters and the like, the attachment means may comprise clips which are adapted in use to be clipped onto the camera body. As yet another alternative the lens attachment may be mounted on the camera lens using a filter holder with grooved supporting arms.

The meniscus lens is conveniently round to suit the majority of cameras, but it may in fact by of any shape.

The present invention also provides a camera comprising a partially reflective lens. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a front view of a lens attachment according to a first embodiment of the present invention; Fig. 2 is a diametral section through the lens attachment of Fig. 1;

Fig. 3 is a front view of a lens attachment according to a second embodiment of the present invention; Fig. 4 is a diametral section through the lens attachment of Fig. 3;

Fig. 5 is a front view of a lens attachment according to a third embodiment of the present invention; - A -

and

Fig. 6 is a diametral section through the lens attachment of Fig. 5.

Referring firstly to Figs. 1 and 2 of the accompanying drawings there is shown a circular lens attachment comprising a thin circular meniscus lens 1 , having a partially reflective coating (not shown) on its front convex surface 2. A mask 3 is provided over the front, convex surface 2 of the meniscus lens 1 and this defines a rectangular aperture, though it may be of any shape to suit the camera with which the lens attachment is to be used.

The meniscus lens 1 is mounted in an annular ring 4 the outer surface of which comprises a threaded portion 5 which facilitates co-axial attachment of the lens attachment to the lens surround of a camera in much the same way as known polarising filters are secured to a camera. However, as an alternative to the screw fitting 5, the annular ring 4 may be provided with a spring or bayonet flange fitting to facilitate attachment to the camera lens surround, or indeed any attachment means appropriate to the camera with which the lens attachment is to be used.

The partially reflective coating on the surface of the meniscus lens 1 typically reflects 50$ of the incident light and transmits 50_/.. Thus, when, in use, the subject of a photograph looks towards the camera the image reflected in the meniscus lens 1 will be

SUBSTITUTESHEET essentially identical to the image which would be seen in the camera view finder. The boundaries of this image are defined by the rectangular mask 3 and the photographer, or indeed the subject, is therefore able to compose the photograph as easily as if he were looking through the camera view finder. The partially reflective lens 1 has little effect on the image forming qualities of the camera lens though it may be necessary to increase the exposure time. The partially reflective costing may be applied either to the front or the rear surface of the meniscus lens 1. If the rear concave surface of the meniscus lens 1 is coated it is somewhat protected from scratches, finger marks and other forms of abuse. However, the protection afforded is offset somewhat by the fact that the reflected image is slightly impaired by a weak secondary reflection from the uncoated front, convex surface of the meniscus lens 1.

Referring now to Figs. 3 and 4 there is shown a square shaped lens attachment. In all essential respects this is identical to the lens attachment of Figs. 1 and 2, except that being square it can be secured in front of the camera lens using a filter holder with grooved supporting arms in the same way that square filters are mounted.

Referring now to Figs. 5 and 6 there is shown a square shaped lens attachment comprising a spring frame 7. The spring frame 7 allows the lens attachment to be clipped on to the camera body in much the same way as some supplementary lenses are secured to some cameras. Interchangeable masks, with different sized aperatures, may be provided to allow the lens attachment to be used with camera lenses of different focal lengths and with cameras having different formats.

The meniscus lens will in general be of zero power (infinite focal length). However, in some circumstances it may be advantageous to incorporate the function of a supplementary close-up lens into the lens attachment. In this case the meniscus lens can be of finite converging power.

The dimensions of the meniscus lens, and the dimensions of the associated mask(s) are chosen to avoid undesirable vignetting of the photographic image.

Indeed, they may be considerably larger than the front of the camera lens if a large reflected image is desired. In all cases, the radius of curvature of the reflective surface is such as to ensure a reflected image having the correct field of view.

The minescus lens of the present invention has been described with reference to the accompanying drawings as an attachment for a camera. However, it may be desirable to actually incorporate the meniscus lens within a camera. This would probably limit the versatility of the camera, but for a camera specifically intended for taking self portraits this would not matter.

SUBSTITUTESHEET

Claims

1. A meniscus lens (1) comprising a partially reflective coating on one face which reflects a portion of incident light and transmits the remainder and which is adapted, in use, to be attached co-axially in front of the lens of a camera with the rear concave surface thereof facing the camera lens.

2. A meniscus lens according to claim 1, wherein the partially reflective coating -reflects approximately 50$ of the incident light.

3- A meniscus lens according to claim 1 or 2, wherein the meniscus lens is of zero power.

4. A meniscus lens according to claim 1 or 2, wherein the meniscus lens is of finite converging power.

5. A meniscus lens according to any preceding claim wherein a mask (3) is mounted on or immediately adjacent to the front convex surface (2) of the meniscus lens (1).

6. A meniscus lens according to any preceding claim, comprising means (4, 5, 7) whereby it can be secured to a camera.

7. A meniscus lens according to claim 6, wherein the attachment means is adapted to engage with existing lens attachment means provided on the camera.

8. A meniscus lens according to claim 6, wherein the attachment means comprises clips (7) which are adapted in use to be clipped onto the camera body.

9. A camera in combination with a meniscus lens

UBSTITUTESHEET according to any of the preceding claims.

SUBSTITUTE SHEET