Lens systems for use in fingerprint detection
DC CAFCFirst Claim
1. An optical system having an optical axis, said system forming an image of an object and comprising:
- a) a prism having a first surface for contacting the object and a second surface, said first surface being oriented with respect to the optical axis at an angle greater than the angle of total internal reflection of the surface;
b) an aperture stop;
c) a first lens unit having a positive power between the aperture stop and the prism for forming a telecentric entrance pupil;
d) a second lens unit having a positive power on the image side of the aperture stop for forming a real image of the object; and
e) a third lens unit between the first and second lens units, said third lens unit having cylindrical power, said cylindrical power being substantially afocal.
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Accused Products
Abstract
Lens systems for use in fingerprint detection systems employing frustrated total internal reflection are provided. The systems include an aperture stop and three lens units. The first lens unit has a positive power, is located on the object side of the aperture stop, and forms a telecentric pupil for the lens system. The second lens unit has a positive power, is located on the image side of the first lens unit, and forms a real image of the object. In certain embodiments, the third lens unit is located between the first and second lens units and has substantially afocal cylindrical power. In other embodiments, the third lens unit serves to correct the field curvature of the image contributed by the first and second lens units.
111 Citations
18 Claims
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1. An optical system having an optical axis, said system forming an image of an object and comprising:
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a) a prism having a first surface for contacting the object and a second surface, said first surface being oriented with respect to the optical axis at an angle greater than the angle of total internal reflection of the surface; b) an aperture stop; c) a first lens unit having a positive power between the aperture stop and the prism for forming a telecentric entrance pupil; d) a second lens unit having a positive power on the image side of the aperture stop for forming a real image of the object; and e) a third lens unit between the first and second lens units, said third lens unit having cylindrical power, said cylindrical power being substantially afocal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An optical system having an optical axis, said system forming an image of an object and comprising:
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a) a prism having a first surface for contacting the object and a second surface, said first surface being oriented with respect to the optical axis at an angle greater than the angle of total internal reflection of the surface; b) an aperture stop; c) a first lens unit having a positive power between the aperture stop and the prism for forming a telecentric entrance pupil; d) a second lens unit having a positive power for forming a real image of the object, said second lens unit being on the image side of the first lens unit; and e) a third lens unit for correcting the field curvature of the image contributed by the first and second lens units. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification