F.θ lens system

Claim 2

An f.θ lens system comprising, in order from a light source side: a first lens unit comprises no more than two lens elements and which has a negative refractive power with a concave surface directed toward the light source side, a second lens unit comprising a positive meniscus lens having a convex surface directed toward the image side, a third lens unit comprising two positive lens elements and one negative lens element and which has a positive refractive power, and a fourth lens unit comprising no more than two plano-convex lens elements and which is spaced along distance from said third lens unit to be located at a position close to an image plane, said lens system further satisfying the following conditions: ##EQU2## where f: focal length of the overall system f I : focal length of the first lens unit f III : focal length of the third lens unit d III IV : distance between the third and fourth lens units f IV : focal length of the fourth lens unit ν II : Abbe number of the second lens unit ν III P1 : Abbe number of a one, situated on the light source side, of said positive lens elements in the third lens unit ν III P2 : Abbe number of a one, situated on the image side, of said positive lens elements in the third lens unit ν III N : Abbe number of the negative lens element in the third lens unit f II III : composite focal length of the second and third lens units.

Claim 3

The f.θ lens system of claim 1, wherein said first lens unit comprises a single lens element.

Claim 4

The f.θ lens system of claim 1, wherein said first lens unit comprises two lens elements.

Claim 5

The f.θ lens system of claim 1, wherein said fourth lens unit comprises a single lens element.

Claim 6

The f.θ lens system of claim 1, wherein said fourth lens unit comprises two lens elements.

Claim 7

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.68 Entrance pupil located ahead of the first surface 60.54 Surface No. r d N ν ______________________________________ 1 -109.779 12.87 1.61405 55.0 2 -708.195 10.11 3 -297.934 37.43 1.48749 70.2 4 -171.096 4.36 5 1454.764 27.87 1.69680 55.5 6 -206.712 39.87 7 1288.277 21.46 1.48749 70.2 8 -754.370 57.19 9 -209.172 13.00 1.74000 28.3 10 -580.912 618.41 11 ∞ 84.79 1.51633 64.1 12 -1086.565 8.00 13 1086.565 84.79 1.51633 64.1 14 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 8

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.70 Entrance pupil located ahead of the first surface 64.98 Surface No. r d N ν ______________________________________ 1 -110.000 26.03 1.51454 54.7 2 -937.216 7.54 3 -323.053 38.00 1.48749 70.2 4 -191.602 1.00 5 1120.729 30.98 1.64850 53.0 6 -204.127 27.63 7 2032.027 38.00 1.69680 55.5 8 -1505.848 50.89 9 -202.801 13.00 1.80518 25.4 10 -442.114 640.44 11 ∞ 71.04 1.51633 64.1 12 -1113.820 8.00 13 1113.820 71.04 1.51633 64.1 14 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 9

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.65 Entrance pupil located ahead of the first surface 77.00 Surface No. r d N ν ______________________________________ 1 -118.298 10.00 1.58913 61.0 2 1807.895 8.11 1.68893 31.1 3 -893.566 9.62 4 -232.653 38.45 1.49700 81.6 5 -175.708 1.00 6 5316.991 26.04 1.77250 49.6 7 -267.213 7.12 8 2922.684 39.84 1.49700 81.6 9 -228.526 31.42 10 -206.286 13.00 1.74000 28.3 11 -730.225 738.62 12 ∞ 62.97 1.51633 64.1 13 -1227.262 8.00 14 1227.262 62.97 1.51633 64.1 15 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 10

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 50.0 f = 749.35 Entrance pupil located ahead of the first surface 78.46 Surface No. r d N ν ______________________________________ 1 -111.215 21.59 1.63854 55.4 2 -690.464 8.25 3 -290.180 38.00 1.48749 70.2 4 -180.385 1.00 5 1321.400 34.22 1.69680 55.5 6 -217.968 37.82 7 1103.738 26.95 1.48749 70.2 8 -608.753 55.80 9 -218.895 13.00 1.74000 28.3 10 -617.952 636.49 11 1182.039 65.96 1.51633 64.1 12 ∞ 56.18 13 1182.039 65.96 1.51633 64.1 14 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 11

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 749.92 Entrance pupil located ahead of the first surface 85.00 Surface No. r d N ν ______________________________________ 1 -118.307 12.20 1.63854 55.4 2 -758.972 12.83 3 -267.384 34.29 1.48749 70.2 4 -184.928 6.53 5 1246.961 48.52 1.69680 55.5 6 -219.951 44.16 7 1221.674 31.57 1.48749 70.2 8 -519.997 31.41 9 -226.019 14.00 1.74000 28.3 10 -568.064 728.50 11 875.046 89.82 1.51633 64.1 12 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 12

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.33 Entrance pupil located ahead of the first surface 85.00 Surface No. r d N ν ______________________________________ 1 -110.000 12.00 1.62299 58.2 2 -715.309 13.93 3 -290.131 42.00 1.58913 61.0 4 -195.187 2.01 5 1401.966 39.76 1.48749 70.2 6 -216.558 6.23 7 1302.920 37.52 1.48749 70.2 8 -340.807 100.58 9 -227.177 14.00 1.74000 28.3 10 -445.519 680.36 11 914.474 85.70 1.51633 64.1 12 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 13

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.70 Entrance pupil located ahead of the first surface 78.95 Surface No. r d N ν ______________________________________ 1 -108.692 19.20 1.50977 62.1 2 -3306.621 6.80 3 -601.838 33.47 1.48749 70.2 4 -172.232 2.00 5 3551.572 27.79 1.80440 39.6 6 -226.013 70.98 7 -220.019 12.00 1.80518 25.4 8 -5930.015 26.78 9 -5458.181 34.36 1.72916 54.7 10 -364.192 695.12 11 ∞ 60.90 1.51633 64.1 12 -1279.349 8.00 13 1279.349 60.90 1.51633 64.1 14 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.

Claim 14

The f.θ lens system of claim 1, further satisfying the following charts: ______________________________________ F.sub.NO = 1:50.0 f = 750.51 Entrance pupil located ahead of the first surface 108.00 Surface No. r d N ν ______________________________________ 1 -104.848 18.01 1.51112 60.5 2 1227.930 38.00 1.72342 38.0 3 -495.112 4.55 4 -568.344 40.00 1.48749 70.2 5 -195.633 17.17 6 -953.790 13.00 1.80518 25.4 7 777.368 10.59 8 948.224 51.19 1.48749 70.2 9 -337.320 1.50 10 2331.561 33.29 1.69680 55.5 11 -752.800 978.03 12 ∞ 50.00 1.51633 64.1 13 -2269.202 8.00 14 2269.202 50.00 1.51633 64.1 15 ∞ ______________________________________ in which F NO signifies the F number, f is the focal length, r is the radius of curvature of an individual lens surface, d is the lens thickness or aerial lens-to-lens distance, N is the refractive index of an individual lens at the d-line, and ν denotes the Abbe number of an individual lens.