F-.theta. lens

• US 5,111,325 A
• Filed: 10/16/1989
• Issued: 05/05/1992
• Est. Priority Date: 10/16/1989
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: DeJager, Donald
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): NGUYEN, THONG Q
• Application Number:
  US07/422,350
• Time in Patent Office: 932 Days
• Field of Search: 350/474, 350/449, 350/433, 350/434, 350/6.1-6.91, 350/415, 350/514, 350/463-473, 350/482, 350/483, 358/302, 359/196-226, 359/662, 359/754, 359/763-783
• US Class Current: 359/206.1
• CPC Class Codes: G02B 13/0005 having F-Theta characteristic scanning systems employing movable or deformable optical elements G02B26/10

Abstract

An f-θ lens is disclosed which is particularly suitable for use with a color laser printer in which beams of different wavelengths are combined into a single combined beam. The combined beam is scanned by a rotating polygon onto a receiving medium. The f-θ is adapted to operate with optics for shaping the beam in a scan direction prior to the polygon and a cylindrical element after the f-θ lens to image the beam in a cross-scan direction onto the receiving medium. In order to provide an f-θ lens which is color corrected, the lens includes means for correcting in a scan direction for lateral color aberrations in each of the beams, and means for correcting in a cross-scan direction for axial color aberrations in each of the beams.

Claims

1. An f-θ

lens, said lens being adapted to receive an input beam which comprises a combination of beams each of which is at a predetermined wavelength and has a predetermined vergence in a scan direction, said lens comprising;

means for correcting in a scan direction for lateral color aberrations of said beams at a receiving medium; and

means for correcting in a scan direction for axial color aberrations of said beams at the receiving medium when at least one of said beams has a non-zero vergence.

2. An f-θ

lens, as defined in claim 1, wherein each of said beams has a wavelength in the infrared.

3. An f-θ

lens, as defined in claim 2, wherein said input beam is a combination of one beam having a wavelength of about 750 nm, a second beam having a wavelength of about 810 nm, and a third beam having a wavelength of about 870 nm.

4. An f-θ

lens, as defined in claim 3, wherein in the scan direction said one beam has a positive vergence, said second beam has zero vergence, and said third beam has a negative vergence.

5. An f-θ

lens comprising in combination a doublet which includes a meniscus negative element and a first meniscus positive element, a second meniscus positive element adjacent said first meniscus positive element, a first double convex positive element adjacent said second meniscus positive element, a second double convex positive element adjacent said first double convex positive element, and a double concave negative element adjacent said second double convex positive element.

6. An f-θ

lens, as defined in claim 5, wherein numerical data of the lens are as follows;

space="preserve" listing-type="tabular">______________________________________ SURF. RADIUS THICKNESS GLASS ______________________________________ Entrance Pupil 30.800 r1 -13.9300 2.500 762265 r2 -50.0263 6.900 651559 r3 -20.6003 0.500 r4 -119.667 5.320 651559 r5 -36.5497 0.500 r6 139.895 5.850 651559 r7 -64.1175 0.500 r8 63.2356 5.190 651559 r9 -269.725 2.517 r10 -93.2760 4.280 785258 r11 71.0150 ______________________________________

where r1-r11 represent radii of curvature of the respective lens elements.

7. An F-θ

lens, said lens being adapted to be used in the optical path of a laser printer comprising a rotatable polygon scanner which provides an input beam composed of a plurality of beams of different wavelengths to the lens and a cylindrical optical element which receives the beam from said lens and directs the beam onto a receiving medium, said lens comprising;

means for correcting in a scan direction for lateral color aberrations of each of said beams; and

means operable with said cylindrical optical element for correcting in a cross-scan direction for axial color aberrations in each of said beams, said means operable with said cylindrical optical element including means for collimating said beam in the cross-scan direction in all of said wavelengths.