Focal length changeable lens

Claim 2

A focal length changeable lens system with its exit pupil located at a long distance for use with an on-chip micro-lens equipped solid-state imaging device, whose focal length is changeable between a long focal length and a short focal length, said lens system comprising: a first lens group having a positive power, said first lens group being movable into an optical axis of the lens system for the long focal length and out of the optical axis for the short focal length; a second lens group having a positive power and disposed on the image end of the lens system relative to said first lens group, said second lens group being movable into the optical axis for the short focal length and out of the optical axis for the long focal length; an aperture stop fixedly disposed in the optical axis between said first lens group and said second lens group; and a third lens group having a positive power, said third lens group being fixedly disposed between said second lens group and the on-chip micro-lens equipped solid-state imaging device in the optical axis so as to place its object focal point near said aperture stop.

Claim 3

A lens system as defined in claim 1, and further comprising a parallel optical element disposed on the side of said third lens group remote from said second lens group and cemented to said third lens group.

Claim 4

A lens system as defined in claim 2, wherein said parallel optical element comprises a low-pass filter.

Claim 5

A lens system as defined in claim 2, wherein said parallel optical element comprises an infrared cut filter.

Claim 6

A lens system as defined in claim 1, and further including a parallel optical filter element (2A), said lens system being comprised of lens elements L 11 -L 14 for said first lens group, lens elements L 15 -L 18 for said second lens group and lens elements L 19 and L 20 for said third lens group substantially as defined in the following table: ______________________________________ Radius of Axial Distance Lens Curvature Between Surfaces Element (mm.) (mm.) N.sub.d V.sub.d ______________________________________ R.sub.11 = 6.800 L.sub.11 d.sub.11 = 2.00 1.79950 42.3 R.sub.12 = 117.519 d.sub.12 = 1.04 R.sub.13 = 19.914 L.sub.12 d.sub.13 = 0.90 1.68893 31.1 R.sub.14 = 5.341 d.sub.14 = 0.80 R.sub.15 = -5.501 L.sub.13 d.sub.15 = 0.90 1.68893 31.1 R.sub.16 = 4.170 d.sub.16 = 1.20 R.sub.17 = 10.707 L.sub.14 d.sub.17 = 2.23 1.71300 53.9 R.sub.18 = -5.166 d.sub.18/19 = 1.47 R.sub.19 = -2.938 L.sub.15 d.sub.20 = 2.00 1.77250 49.6 R.sub.20 = -3.276 d.sub.21 = 0.10 R.sub.21 = 7.123 L.sub.16 d.sub.22 = 1.25 1.77250 49.6 R.sub.22 = -10.785 d.sub.23 = 0.45 R.sub.23 = -4.359 L.sub.17 d.sub.24 = 1.50 1.84666 23.8 R.sub.24 = 234.195 d.sub.25 = 1.05 R.sub.25 = -4.141 L.sub.18 d.sub.26 = 1.25 1.77250 49.6 R.sub.26 = -3.926 d.sub.27 = 3.56 R.sub.27 = 15.550 L.sub.19 d.sub.28 = 1.60 1.62041 60.3 R.sub.28 = Infinity d.sub.29 = 0.10 R.sub.29 = 15.550 L.sub.20 d.sub.30 = 1.60 1.62041 60.3 R.sub.30 = Infinity d.sub.31 = 0.00 R.sub.31 = Infinity 2A d.sub.32 = 5.00 1.51633 64.1 R.sub.32 = Infinity ______________________________________ where the lens elements L 11 to L 20 and the parallel optical element (2A) have surfaces R 11 to R 32 , the axial distance between adjacent surfaces being given by d 11 to d 32 , the index of refraction being given by N d , and the dispersion measured by the Abbe No. as given by V d .

Claim 7

A lens system as defined in claim 1, and further including a parallel optical filter element (2B), said lens system being comprised of lens elements L 21 -L 24 for said first lens group, lens elements L 25 -L 28 for said second lens group and lens elements L 29 and L 30 for said third lens group substantially as defined in the following table: ______________________________________ Radius of Axial Distance Lens Curvature Between Surfaces Element (mm.) (mm.) N.sub.d V.sub.d ______________________________________ R.sub.41 = 6.998 L.sub.21 d.sub.41 = 2.00 1.79950 42.3 R.sub.42 = 61.139 d.sub.42 = 1.29 R.sub.43 = 18.431 L.sub.22 d.sub.43 = 0.90 1.68893 31.1 R.sub.44 = 5.687 d.sub.44 = 0.72 R.sub.45 = -5.724 L.sub.23 d.sub.45 = 0.90 1.68893 31.1 R.sub.46 = 4.154 d.sub.46 = 1.10 R.sub.47 = 11.435 L.sub.24 d.sub.47 = 2.55 1.71300 53.9 R.sub.48 = -4.980 d.sub.48/49 = 1.15 R.sub.49 = -2.772 L.sub.25 d.sub.50 = 1.80 1.77250 49.6 R.sub.50 = -3.178 d.sub.51 = 0.10 R.sub.51 = 8.319 L.sub.26 d.sub.52 = 1.15 1.69680 55.6 R.sub.52 = -7.845 d.sub.53 = 0.57 R.sub.53 = -3.668 L.sub.27 d.sub.54 = 1.30 1.80518 25.5 R.sub.54 = -23.359 d.sub.55 = 0.65 R.sub.55 = -4.429 L.sub.28 d.sub.56 = 1.25 1.77250 49.6 R.sub.56 = -3.954 d.sub.57 = 4.04 R.sub.57 = Infinity L.sub.29 d.sub.58 = 1.60 1.62041 60.3 R.sub.58 = -15.550 d.sub.59 = 0.10 R.sub.59 = 15.550 L.sub.30 d.sub.60 = 1.60 1.62041 60.3 R.sub.60 = Infinity d.sub.61 = 0.00 R.sub.61 = Infinity 2B d.sub.62 = 5.00 1.51633 64.1 R.sub.62 = Infinity ______________________________________ where the lens elements L 21 to L 30 and the parallel optical element (2B) have surfaces R 41 to R 62 , the axial distance between adjacent surfaces being given by d 41 to d 62 , the index of refraction being given by N d , and the dispersion measured by the Abbe No. as given by V d .