Objective lens system for endoscopes
First Claim
Patent Images
1. An objective lens system for endoscopes, comprising, in order from the object side:
- a front lens unit including a negative lens component and a positive lens component;
an aperture stop; and
a rear lens unit having a positive refractive power;
whereinsaid aperture stop is disposed substantially at a front focal point of said rear lens unit; and
at least said rear lens unit includes an aspherical surface satisfying the following condition (1);
space="preserve" listing-type="equation">E'"'"'(n.sub.i-1 -n.sub.i)>
0 (1)wherein the reference symbol E'"'"' represents the aspherical surface coefficient of fourth order, the reference symbol ni-1 designates the refractive index of a medium disposed on the object side of said aspherical surface, and the reference symbol ni denotes the refractive index of the medium disposed on the image side of said aspherical surface.
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Abstract
A nearly telecentric objective lens system for endoscopes comprising an aperture stop, and a lens unit which has a positive refractive power and is arranged after said aperture stop, wherein said aperture stop is located at the front focal point of said positive lens unit and a single aspherical surface or a plurality of aspherical surfaces are arranged only in said positive lens unit. Distortion is corrected favorably in the objective lens system for endoscopes.
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Citations
14 Claims
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1. An objective lens system for endoscopes, comprising, in order from the object side:
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a front lens unit including a negative lens component and a positive lens component; an aperture stop; and a rear lens unit having a positive refractive power;
whereinsaid aperture stop is disposed substantially at a front focal point of said rear lens unit; and at least said rear lens unit includes an aspherical surface satisfying the following condition (1);
space="preserve" listing-type="equation">E'"'"'(n.sub.i-1 -n.sub.i)>
0 (1)wherein the reference symbol E'"'"' represents the aspherical surface coefficient of fourth order, the reference symbol ni-1 designates the refractive index of a medium disposed on the object side of said aspherical surface, and the reference symbol ni denotes the refractive index of the medium disposed on the image side of said aspherical surface. - View Dependent Claims (2, 8, 9, 10, 11, 12, 13, 14)
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3. An objective lens system for endoscopes comprising, in the order from the object side, a front lens unit comprising a negative lens component, an aperture stop and a rear lens unit having a positive refractive power:
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said aperture stop being located substantially at the front focal point of said positive lens unit; and said rear lens unit comprising at least one aspherical surface at a location satisfying the following conditions (5) and (6);
space="preserve" listing-type="equation">|hm/r.sub.s |>
0.5 (5)
space="preserve" listing-type="equation">|hc/I/51 >
0.5 (6)wherein the reference symbol hm represents the height of the marginal ray on said aspherical surface, the reference symbol hc designates the height, on said aspherical surface, of the principal ray to attain to the maximum image height, the reference symbol rs denotes the radius of the aperture of said aperture stop, and the reference symbol I represents the maximum image height. - View Dependent Claims (4, 5)
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6. An objective lens system for endoscopes comprising, in order from the object side;
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a front lens unit comprising a negative lens component; an aperture stop; and a rear lens unit having a positive refractive power;
whereinsaid aperture stop is disposed substantially at the front focal point of said rear lens unit; and at least said rear lens unit including an aspherical surface satisfying the following conditions (1) and (2);
space="preserve" listing-type="equation">E.sub.i '"'"'(n.sub.i-1 -n.sub.i)>
0 (1)ω
≦
I/f≦
0.9 tan (ω
/0.9) (2)wherein the reference symbol Ei '"'"' represents an aspherical surface coefficient of fourth order, the reference symbol ni-1 designates the refractive index of a medium disposed on the object side of said aspherical surface, the reference symbol ni denotes the refractive index of a medium disposed on the image side of said aspherical surface, the reference symbol ω
represents a half field angle of said objective lens system, the reference symbol I designates maximum image height and reference symbol f denotes focal length of the objective lens system as a whole.
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7. An objective lens system for endoscopes comprising, in order from the object side;
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a front lens unit; an aperture stop; and a rear lens unit having a positive refractive power;
wherein;said aperture stop is disposed substantially at the front focal point of said rear lens unit; and only said rear lens unit includes an aspherical surface satisfying the following conditions (1) and (2);
space="preserve" listing-type="equation">E.sub.i '"'"'(n.sub.i-1 -n.sub.i)>
0 (1)
space="preserve" listing-type="equation">ω
≦
I/f≦
0.9 tan (ω
/0.9) (2)wherein the reference symbol Ei '"'"' represents an aspherical surface coefficient of fourth order, the reference symbol ni-1 designates the refractive index of a medium disposed on the object side of said aspherical surface, the reference symbol ni denotes the refractive index of a medium disposed on the image side of said aspherical surface, the symbol ω
represents a half field angle of said objective lens system, the reference symbol I designates maximum image height and the reference symbol f denotes focal length of the objective lens system as a whole.
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Specification