US 5,900,987 AGranted

Zoom projection lenses for use with pixelized panels

AssigneeU.S. Precision Lens Incorporated

InventorMelvyn H. Kreitzer

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Abstract

A zoom projection lens for use with LCD or DMD panels is provided. The lens has two units U1 and U2, which are moved relative to one another for zooming. The first unit has a negative power and includes at least three lens elements L1, L2, and L3, where L1 is composed of plastic and has two aspherical surfaces, L2 has a positive power and is composed of a flint material, and L3 has a negative power and is composed of a crown material. The second unit has two subunits U2.sub.S1 and U2.sub.S2, each of which has a positive power, with the power of U2.sub.S2 being greater than the power of U2.sub.S1. At its minimum effective focal length f.sub.min, the projection lens has a back focal length to focal length ratio greater than one, the ratio being achieved by arranging the first unit, the second unit, and the subunits of the second unit so that: D.sub.12 /f.sub.min >1.0, D.sub.S1S2 /f.sub.min >1.0, and D.sub.12 /D.sub.S1S2 >1.0, where D.sub.12 is the axial distance between the first and second lens units evaluated at f.sub.min and D.sub.S1S2 is the axial distance between the first and second subunits of the second lens unit.

A projection lens for forming an image of an object, said lens having an aperture stop and a zoom range between a minimum effective focal length and a maximum effective focal length, said lens comprising in order from its image end to its object end:

(A) a first lens unit having a negative power and comprising a first lens element, which has at least one aspherical surface, and at least two other lens elements, one of which has a positive power and the other of which has a negative power, the dispersion of the positive lens element being greater than the dispersion of the negative lens element;
(B) a second lens unit separated from the first lens unit by an axial space, said second lens unit having a positive power and comprising a first lens subunit on the image side of the second lens unit and a second lens subunit on the object side of the second lens unit, wherein each of said subunits has a positive power, the power of the second lens subunit is greater than the power of the first lens subunit, and the lens' aperture stop is located within the first lens subunit or is closer to the first lens subunit than to either the first lens unit or the second lens subunit for the lens having its minimum effective focal length;
and
(C) zoom means for varying the lens' effective focal length over the zoom range by changing the axial space between the first and second lens units;
wherein:
D.sub.12 /f.sub.min >1.0,
D.sub.S1S2 /f.sub.min >1.0,
D.sub.12 /D.sub.S1S2 >1.0,
and
BFL/f.sub.min >1.0,
where:
(i) f.sub.min is the minimum effective focal length of the lens;
(ii) BFL is the back focal length of the lens in air for an object located at infinity along the long conjugate side of the projection lens and for the lens having its minimum effective focal length;
(iii) D.sub.12 is the axial distance between the first and second lens units for the lens having its minimum effective focal length;
and
(iv) D.sub.S1S2 is the axial distance between the first and second subunits of the second lens unit.

13 more elements

Abstract

Claims9