# US 5,703,727 A · Zoom lens and magnifier utilizing the same

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- Number: US 5,703,727 A
- Document ID: US5703727A
- Status: Granted
- Kind: A
- Application number: 08/279,059
- Filed: 1994-07-22
- Granted: 1997-12-30
- Earliest claimed: 1994-07-22
- Assignees: Telesensory Corporation
- Inventors: John A. Lawson; W. Andrew Morrison; Rob E. Savoie
- Web page: https://patentgrep.com/patent/US5703727A

## CPC

- G02B 25/008: {comprising two or more lenses (G02B25/004 - G02B25/007 take precedence)}
- G02B 7/10: by relative axial movement of several lenses, e.g. of varifocal objective lens
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A zoom lens is described which is quite simple and yet provides a wide (5:1) zoom range. The lens consists of a front focusing negative lens which provides a stationary virtual image for two rear zooming lens groups. These two zooming groups are positive and reimage the object at a camera pickup device. Such zooming groups are of substantially equal focal length and bear equally in the magnification change. The invention includes a magnifier which utilizes the zoom lens and has the mechanical aspects necessary to provide the needed lens motions.

## Claims

### Claim 1

A magnifier for enhancing the visual projection of an object comprising, in combination:
(A) a support for an object to be magnified;
(B) a focusing lens group positioned on an optic axis to gather light from an object at said support;
(C) a focus control manipulatable by an operator of said magnifier and connected to said focusing lens group for moving the latter on said optic axis to focus an image of said object at an image plane;
(D) a pair of zoom lens groups positioned on said optic axis between said focusing lens group and said image plane;
(E) motion linkage connected to said zoom lens groups for moving the latter along said axis relative to one another between said focusing lens group and said image plane to change the magnification of said image of said object at said image plane;
(F) a zoom control manipulatable by an operator of said magnifier, connected to said motion linkage to enable manipulation of said zoom lens groups by said operator to obtain a desired magnification;
(G) an image pickup device positioned at said image plane to receive said image of said object;
(H) an electrically operable monitor in communication with said pickup device adapted to display an enlarged view of said image of said object;
(I) said motion linkage being connected to said zoom lens groups to move the same along said axis in a range between said focusing lens group and said image plane so as not to require movement of said focusing lens group to focus said image at said image plane after operation of said motion linkage: and
(J) the magnification of each of said zoom lens groups being generally of the same positive power as that of the other, and said focusing lens group consisting of one negative focusing lens and each of said positive power zoom lens groups consisting of two lenses.

### Claim 2 (depends on 1)

The magnifier of claim 1 wherein the focal length of each of said zoom lens groups is generally the same as the focal length of the other.

### Claim 3 (depends on 1)

The magnifier of claim 1 wherein said motion linkage connected to said pair of zoom lens groups is adapted to move said groups relative to one another and relative to said focusing lens and image plane to change the magnification over a range of from unity to 1/5.

### Claim 4 (depends on 1)

The magnifier of claim 1 wherein said lens groups consist of individual lens elements, at least one of which is plastic.

### Claim 5 (depends on 4)

The magnifier of claim 4 wherein each of said individual lens elements is a plastic lens consisting primarily of a plastic resin selected from the group consisting of polymethylmethacrylate, polycarbonate and polystyrene.

### Claim 6 (depends on 1)

A magnifier according to claim 1 further including as part of said combination, a mirror positioned between said support and said focusing lens group to direct light defining the object to said focusing lens group.

### Claim 7 (depends on 1)

The magnifier of claim 1 wherein said zoom lens groups are grouped together for concurrent movement.