Color corrected projection lenses employing diffractive optical surfaces

• US 6,529,336 B1
• Filed: 05/11/2001
• Issued: 03/04/2003
• Est. Priority Date: 11/12/1998
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: US Precision Lens, Inc. (3M Company)
• Inventors: Kreitzer, Melvyn H.
• Primary Examiner(s): Mack, Ricky
• Application Number:
  US09/831,597
• Time in Patent Office: 662 Days
• Field of Search: 359/648-651, 359/713-716, 359/753, 359/782, 359/784, 359/788, 359/708, 348/776, 348/778, 348/779, 348/781
• US Class Current: 359/649
• CPC Class Codes: G02B 13/16 for use in conjunction with image converters or intensifiers , or for use with projectors, e.g. objectives for projection TV
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4216 correcting geometrical aberrations
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path

Abstract

A projection television system (10) is provided which has a CRT (16) and a projection lens system (13) for forming an image on a screen (14). The projection lens system (13) is characterized by a diffractive optical surface (DOS) which provides color correction for the lens system. The diffractive optical surface (DOS) can be formed as part of a diffractive optical element (DOE) or as part of an existing lens element of the lens system. The diffractive optical surface (DOS) is located between the object side (S2) of the lens'"'"' first lens unit (U1) and the image side (S11) of the lens'"'"' third lens unit (U3). The distance between the diffractive optical surface (DOS) and the lens'"'"' aperture stop (AS) is less than 0.1·f₀, where f₀ is the focal length of the projection lens (13).

Claims

1. A projection lens system for use with a cathode ray tube, said projection lens system having a long conjugate side and a short conjugate side and comprising in order from its long conjugate side:

(a) a first lens unit which primarily corrects aperture dependent aberrations, said first lens unit having a short conjugate side and comprising at least one aspherical surface;

(b) a second lens unit having a positive optical power;

(c) a corrector lens unit comprising at least one aspherical surface; and

(d) a third lens unit which is associated with the cathode ray tube during use of the lens system and which provides correction for the field curvature of the lens system, said third lens unit having a long conjugate side;

wherein the lens system includes at least one diffractive optical surface which at least partially corrects the axial color of the lens system and which is located between the short conjugate side of the first lens unit and the long conjugate side of the third lens unit.

2. The projection lens system of claim 1 wherein the diffractive optical surface is formed on a diffractive optical element which comprises two optical surfaces, one of said optical surfaces being plano and the other of said optical surfaces being the diffractive optical surface.

3. The projection lens system of claim 1 wherein:

(i) the projection lens system has an aperture stop and a focal length f₀, and

(ii) the distance between the diffractive optical surface and the aperture stop is less than 0.1·

f₀.

4. The projection lens system of claim 3 wherein the distance between the diffractive optical surface and the aperture stop is less than 0.05·

f₀.

5. A projection television system comprising a cathode ray tube and a projection lens system for projecting light from the cathode ray tube onto a screen to form an image, said projection lens system comprising the projection lens system of claim 1.

6. A projection television system comprising three cathode ray tubes and three projection lens systems, one projection lens system being associated with each of the cathode ray tubes for projecting light from that tube onto a common screen to form an image, each projection lens system comprising the projection lens system of claim 1.