Projection lenses having larger back focal length to focal length ratios

• US 5,870,228 A
• Filed: 05/16/1997
• Issued: 02/09/1999
• Est. Priority Date: 05/24/1996
• Status: Expired due to Term

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: US Precision Lens, Inc.
• Inventors: Moskovich, Jacob, Kreitzer, Melvyn H.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BEY, DAWN MARIE
• Application Number:
  US08/857,358
• Time in Patent Office: 634 Days
• Field of Search: 359/649, 359/650, 359/651, 359/689, 359/784-792, 349/5, 349/57, 349/62
• US Class Current: 359/649
• CPC Class Codes: G02B 13/04 Reversed telephoto objectives
• CPC Class Codes: G02B 13/18 with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration G02B13/002 takes precedence
• CPC Class Codes: G02B 9/12 having three components only

Abstract

A projection lens for use with LCD or DMD panels is provided. The lens has three lens units, the first unit having a negative power and at least one plastic lens element having two aspheric surfaces, a second lens unit having a negative power or a weak positive power and at least one color correcting doublet, and a third lens unit having a positive power and an aspheric surface either on a glass element or on a weak plastic element. The projection lens has a back focal length to focal length ratio of at least 3.0, the ratio being achieved by arranging the first, second, and third lens units so that:

D₁₂ /f₀ >1.0,

D₂₃ /f₀ >0.7, and

1.5<(D₁₂ +D₂₃ +BFL)/BFL<4.0

where: f₀ is the effective focal length of the combination of the first, second, and third lens units; BFL is the back focal length of the combination of the first, second, and third lens units; D₁₂ is the distance between the first and second lens units; and D₂₃ is the distance between the second and third lens units.

Claims

1. A projection lens for forming an image of an object, said lens consisting in order from its image end to its object end of:

(a) an first lens unit composed exclusively of plastic;

(b) a second lens unit air spaced from the first lens unit and consisting of a plurality of glass lens elements; and

(c) a third lens unit air spaced from the second lens unit and consisting of a plurality of glass lens elements;

wherein;

space="preserve" listing-type="equation">D.sub.12 /f.sub.0 >

1.0

where;

(i) f₀ is the effective focal length of the combination of the first, second, and third lens units; and

(ii) D₁₂ is the distance between the first and second lens units.

2. The projection lens of claim 1 wherein the maximum clear aperture of the first lens unit is larger than the maximum clear apertures of both the second and third lens units.

3. A projection lens system for forming an image of an object, said system comprising:

(a) an illumination system comprising a light source and illumination optics which forms an image of the light source, said image of the light source being the output of the illumination system;

(b) a pixelized panel which comprises the object; and

(c) the projection lens of claim 2.

4. The projection lens of claim 1 wherein the first lens unit has at least one aspheric surface which contributes to the correction of the projection lens'"'"' distortion.