Objective lens for use with information storage disks

Claim 2

An objective lens for use with an information storage disk comprising a three-component, three-element lens system including a first component composed of a positive-meniscus lens having a convex side directed toward a light source, a second component composed of a negative-meniscus lens having a concave side directed toward the light source, and a third component composed of a positive-meniscus lens having a convex side directed toward the light source, said objective lens satisfying the following requirements: (1) 1.8F<F 1 <2.5F (2) |F 2 |>25F (3) 1.2F<F 3 <1.8F (4) d 4 <0.3F where F is the overall focal length of the lens system, F 1 is the focal length of the first component, F 2 is the focal length of the second component, F 3 is the focal length of the third component, and d 4 is the air spacing between the second and third components.

Claim 3

The objective lens of claim 1 further comprising a cover glass disposed between the objective lens system and the disk and system further satisfying the following table: ______________________________________ r.sub.1 = 8.136 d.sub.1 = 1.500 N.sub.1 = 1.86890 r.sub.2 = 158.717 d.sub.2 = 0.800 r.sub.3 = -4.236 d.sub.3 = 1.500 N.sub.2 = 1.78569 r.sub.4 = -4.819 d.sub.4 = 0.300 r.sub.5 = 3.834 d.sub.5 = 1.500 N.sub.3 = 1.86890 r.sub.6 = 8.915 ______________________________________ F = 4.50 N.A. = 0.50 W.sub.t = 2.00 t = 1.20 N.sub.t = 1.49 F.sub.1 = 2.18F |F.sub.2 | = 74.99F F.sub.3 = 1.51F ______________________________________ where W t is the air spacing or operating distance between the objective lens system and a cover glass for the information storage disk, t is the thickness of the cover glass, and N t is the refractive index of the cover glass.

Claim 4

The objective lens of claim 1 further comprising a cover glass disposed between the objective lens system and the disk and further satisfying the following table: ______________________________________ r.sub.1 = 7.235 d.sub.1 = 1.346 N.sub.1 = 1.86890 r.sub.2 = 88.984 d.sub.2 = 0.677 r.sub.3 = -4.157 d.sub.3 = 1.500 N.sub.2 = 1.78569 r.sub.4 = -4.706 d.sub.4 = 0.300 r.sub.5 = 4.048 d.sub.5 = 1.498 N.sub.3 = 1.86890 r.sub.6 = 9.139 ______________________________________ F = 4.50 N.A. = 0.50 W.sub.t = 2.00 t = 1.20 N.sub.t = 1.49 F.sub.1 = 2.00F |F.sub.2 | = 49.85F F.sub.3 = 1.63F ______________________________________ where W t is the air spacing or operating distance between the objective lens system and a cover glass for the information storage disk, t is the thickness of the cover glass, and N t is the refractive index of the cover glass.

Claim 5

The objective lens of claim 1 further comprising a cover glass disposed between the objective lens system and the disk and further satisfying the following table: ______________________________________ r.sub.1 = 7.502 d.sub.1 = 1.500 N.sub.1 = 1.78569 r.sub.2 = 1000.000 d.sub.2 = 0.800 r.sub.3 = -4.249 d.sub.3 = 1.481 N.sub.2 = 1.78569 r.sub.4 = -4.805 d.sub.4 = 0.300 r.sub.5 = 3.712 d.sub.5 = 1.412 N.sub.3 = 1.86890 r.sub.6 = 7.982 ______________________________________ F = 4.50 N.A. = 0.50 W.sub.t = 2.00 t = 1.20 N.sub.t = 1.49 F.sub.1 = 2.14F |F.sub.2 | = 60.38F F.sub.3 = 1.54F ______________________________________ where W t is the air spacing or operating distance between the objective lens system and a cover glass for the information storage disk, t is the thickness of the cover glass, and N t is the refractive index of the cover glass.