US 5,327,291 AGranted

Compact objective lens

AssigneePolaroid Corporation

InventorsJames G. Baker, William T. Plummer, Jon Van Tassell

Life of this patent

Estimating the term…

Loading patent…

Abstract

A lens system for a folding reflex camera is provided. The system includes: (a) a first group on the object side of the system's stop which (i) has a positive dioptric power, (ii) includes an aspheric surface, and (iii) has a concave surface adjacent to the stop; and (b) a second group on the image side of the stop consisting of either a single positive component or the combination of a single positive component and one or more focusing elements. The system includes at least two elements made of materials differing in dispersive powers where at least one of the elements is of plastic. The system can comprise just two plastic elements and even with such a simple configuration achieves excellent optical performance including a relatively flat field, relatively low distortion, and at least partial correction for lateral chromatic aberration.

Claims18

Dependent claims

A lens system for use in forming an image on a flat or weakly concave recording surface which has a half-diagonal length D.sub.1/2, said lens system (i) having an equivalent focal length f.sub.0, (ii) a diotropic power K.sub.0, and (iii) including a stop or aperture, said lens system comprising:

(a) a first group on the object side of the stop or aperture having a positive dioptric power K.sub.1 which is in the range from about 0.2 to about 0.5 times K.sub.0, said first group comprising a concave surface preceding and adjacent to the stop or aperture, said concave surface having a radius of curvature, if spherical, or a central radius of curvature, if aspheric, lying in the range from about 0.1 to about 0.25 times f.sub.0, the vertex or axial point of said concave surface lying within a distance along the lens system's optical axis from the axial point of the stop or aperture not greater than about 1/20 times f.sub.0 ;
and
(b) a second group on the image side of the stop or aperture consisting of a single component comprising one or more lens elements, said single component having:
(i) only two air surfaces;
(ii) a positive power;
(iii) a front vertex which lies axially to the rear of the axial point of the stop or aperture at a distance not greater than about 1/20 times f.sub.0 ;
(iv) an axial thickness not greater than about 1/20 times f.sub.0 ;
and
(v) a forward surface adjacent to the stop or aperture having a curvature, if spherical, or an axial or central curvature, if aspheric, lying in the range from about -2.0 to about +1.5 times K.sub.0 ;
said lens system:
(i) having a total diagonal field of view not exceeding about 62 degrees;
(ii) having an average field curvature whose magnitude in any azimuth does not exceed about 0.1 times K.sub.0 ;
(iii) having a distortion not exceeding about 5% of D.sub.1/2 ;
(iv) being corrected at least partially for lateral chromatic aberration;
and
(v) having at least two elements made of materials differing in dispersive powers, at least one of the two elements is plastic.

13 more elements

A lens system for use in forming an image on a flat or weakly concave recording surface which has a half-diagonal length D.sub.1/2, said lens system (i) having an equivalent focal length f.sub.0, (ii) a dioptric power K.sub.0, and (iii) including a stop or aperture, said lens system comprising:

(a) a first group on the object side of the stop or aperture having a positive dioptric power K.sub.1 which is in the range from about 0.2 to about 0.5 times K.sub.0, said first group comprising:
(i) a concave surface preceding and adjacent to the stop or aperture, said concave surface having a radius of curvature, if spherical, or a central radius of curvature, if aspheric lying, in the range from about 0.1 to about 0.25 times f.sub.0, the vertex or axial point of said concave surface lying within a distance along the lens system's optical axis from the axial point of the stop or aperture not greater than about 1/20 times f.sub.0 ;
and
(ii) at least one aspheric surface;
and
(b) a second group on the image side of the stop or aperture consisting of two separated subgroups,
the first of said two separated subgroups comprising focusing means for focusing the lens system as a whole over a range of object distances from infinity down to about 4.0 times f.sub.0, object distances being measured from the axial point of the object surface along the axis to the vertex of the first lens surface on the long conjugate side of the lens system, and
the second of said two separated subgroups consisting of a single component comprising one or more lens elements, said single component having:
(i) only two air surfaces;
(ii) a positive power;
(iii) a front vertex which lies axially to the rear of the axial point of the stop or aperture at a distance not greater than about 1/20 times f.sub.0, said distance containing wholly within it said first of said two separated subgroups;
(iv) an axial thickness not greater than about 1/20 times f.sub.0 ;
and
(v) a forward surface having a curvature, if spherical, or an axial or central curvature, if aspheric, lying in the range from about -2.0 to about +1.5 times K.sub.0 ;
said lens system:
(i) having a total diagonal field of view not exceeding about 62 degrees;
(ii) having an average field curvature whose magnitude
in any azimuth does not exceed about 0.1 times K.sub.0 ;
(iii) having a distortion not exceeding about 5% of D.sub.1/2 ;
(iv) being corrected at least partially for lateral chromatic aberration;
and
(v) having at least two elements made of plastic materials differing in dispersive powers.

19 more elements

Dependencies are inferred from the claim text.