Two-mirror systems for periscopic rearward viewing

Claim 2

A periscope providing an erect and unreversed view at an intended viewing position of an extended object field and comprised of a first cylindrically concave mirror, a second cylindrically concave mirror, and means supporting and positioning said mirrors so that the cylindrical axes of both mirrors are substantially parallel and said first mirror reflects light from said object field to said second mirror and said second mirror reflects light from said object field and said first mirror to said intended viewing position, wherein the distortion and astigmatism in the image of said object field as formed by reflection from said first mirror only are largely removed in said view at the intended viewing position by the reflection of said image by said second mirror.

Claim 3

A periscope in accordance with claim 2 wherein the curvature of at least one of the mirrors, in cross-sections perpendicular to their cylinder axes, is continuously changing from point to point along the length of the mirror curve.

Claim 4

A periscope in accordance with claim 2 wherein the converging length of said first mirror along the ray path from a point near or at the center of said extended object field to the approximate center of said intended viewing position is substantially equal to the converging length of said second mirror along the same ray path.

Claim 5

A periscope in accordance with claim 2 wherein the converging length of said first mirror along the ray paht from a selected point near or at the center of said extended object field to the approximate center of said intended viewing position added to the converging length of said second mirror along the same ray path is substantially equal to the distance between the two mirrors along the ray path.

Claim 6

A periscope in accordance with claim 4 and wherein said converging lengths of said first and second mirrors are substantially equal.

Claim 7

A periscope in accordance with claim 5 with the curves of said mirrors further controlled so as to minimize the amounts of distortion and astigmatism throughout said object field.

Claim 8

A periscope in accordance with claim 6 in which the amount of distortion in the view of object points B and A is determined by the expression: ##EQU11## where γ B -γ A is the angle between the projected central rays from object points B and A in their paths between said second mirror and said intended viewing position and α B -α A is the angle between the projected central rays from object points B and A in their paths from said object field to said first mirror, and in which the amount of astigmatism S in the view of any object point A within said object field is determined by the expression: ##EQU12## where the subscript 1 denotes quantities associated with said first mirror, the subscript 2 denotes quantities associated with said second mirror, the subscript a denotes quantities pertaining to a projected central ray from said point A, r denotes the instantaneous radius of curvature of a mirror at the point of intersection of its surface with the same projected central ray, β denotes the angle between the same projected central ray and the normal to the mirror surface at the point of intersection of the surface and the projected central ray, q denotes the distance between the points of intersection of said first and second mirrors with the same projected central ray; the quantities r and q being measured in millimeters.

Claim 9

A periscope in accordance with claim 7 in which the quantities D and S are evaluated through the use of relationships which are based in part on the first and second derivatives of the mirror curves.

Claim 10

A periscope in accordance with claim 1 wherein the first mirror is positioned to the side of the second mirror.

Claim 11

A periscope in accordance with claim 9 and scaled and located for viewing use by the operator of a vehicle, with said means supporting and positioning the mirrors with their cylinder axes approximately vertical and in an intended spaced relationship to said vehicle.

Claim 12

A periscope in accordance with claim 10 in which the mirrors are so constructed and arranged that the leftward portion of the object field is reflected from the rightward portion of said first mirror.

Claim 13

A periscope in accordance with claim 10 and wherein the light proceeding from said object field to said second mirror travels laterally relative to the vehicle in its path between said first and second mirrors.

Claim 14

A periscope in accordance with claim 10 and in which said second mirror is located approximately centrally in front of said operator.

Claim 15

A periscope in accordance with claim 10 and wherein the positioning and supporting means for said second mirror is adjustable about an axis substantially parallel to the cylinder axis of said second mirror for the purpose of permitting the operator to see the full extent of said view while maintaining a comfortable position.

Claim 16

A periscope in accordance with claim 10 and wherein said first mirror is also positioned forwardly of a side edge of the vehicle windshield and light proceeding from said object field to said second mirror travels through the windshield in its path between said first and second mirrors.

Claim 17

A periscope in accordance with claim 10 and wherein said first and second mirrors and said means supporting and positioning the mirrors are housed in a single enclosure which may be sealed against the entry of materials damaging to the reflections from said mirrors and which is intended for fastening to a part of the vehicle structure.

Claim 18

The combination of a periscope in accordance with claim 10 in which the mirrors are so constructed and arranged that said view is of an object field to the rearward and mainly to the left with another such periscope in which said view is of an object field to the rearward and mainly to the right.

Claim 19

A periscope in accordance with claim 17 in which said object field to the rearward and mainly to the left is reflected by a first mirror which is to the left side of a cooperating second mirror and said object field to the rearward and mainly to the right is reflected by another first mirror which is to the right side of another cooperating second mirror.

Claim 20

A periscope in accordance with claim 1 wherein the magnification in the view direction which is perpendicular to the cylinder axes of the mirrors has a prescribed value and is substantially constant, the magnification in the view direction parallel to the cylinder axes is substantially unity.