Variable focal length optical system
First Claim
1. A variable focal length optical system consisting of, in succession from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,wherein when a focal length of the entire lens system is changed while maintaining a constant image plane position, said second lens unit moves in an optical axis direction, said third lens unit moves in the optical axis direction to compensate for variations in image plane position upon movement of said second lens unit, and said first and fourth lens units are fixed in position in the optical axis direction,an aperture stop is disposed at a position on an object side of a position closest to the image side of said third lens unit,said third lens unit is constituted by a negative sub unit disposed on the object side, and a positive sub unit disposed on the image side of said negative sub unit,said negative sub unit includes at least one negative lens, and said positive sub unit includes at least one positive lens, andsaid negative and positive sub units are disposed to be separated by a gap.
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Accused Products
Abstract
A variable focal length optical system is constituted by, in succession from an object side, a first lens unit G1 having a negative refractive power, a second lens unit G2 having a positive refractive power, a third lens unit G3 having a negative refractive power, and a fourth lens unit G4 having a positive refractive power. When the focal length of the entire lens system is changed while maintaining a constant image plane position, the second lens unit G2 moves in the optical axis direction, the third lens unit G3 moves in the optical axis direction to compensate for variations in image plane position upon movement of the second lens unit G2, and the first lens unit G1 and the fourth lens unit G4 are fixed in position in the optical axis direction. An aperture stop is disposed at a position on the object side of a position closest to the image side of the third lens unit G3, or each of the first to fourth lens units G1 to G4 is constituted by two or less lens elements.
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Citations
24 Claims
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1. A variable focal length optical system consisting of, in succession from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,
wherein when a focal length of the entire lens system is changed while maintaining a constant image plane position, said second lens unit moves in an optical axis direction, said third lens unit moves in the optical axis direction to compensate for variations in image plane position upon movement of said second lens unit, and said first and fourth lens units are fixed in position in the optical axis direction, an aperture stop is disposed at a position on an object side of a position closest to the image side of said third lens unit, said third lens unit is constituted by a negative sub unit disposed on the object side, and a positive sub unit disposed on the image side of said negative sub unit, said negative sub unit includes at least one negative lens, and said positive sub unit includes at least one positive lens, and said negative and positive sub units are disposed to be separated by a gap.
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7. A variable focal length optical system comprising, in succession from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,
wherein when a focal length of the entire lens system is changed while maintaining a constant image plane position, said second lens unit moves in an optical axis direction, said third lens unit moves in the optical axis direction to compensate for variations in image plane position upon movement of said second lens unit, and said first and fourth lens units are fixed in position in the optical axis direction, and each of said first to fourth lens units is constituted by not more than two lens elements, wherein a negative lens is disposed at a position closest to the image side in said first lens unit, and said negative lens satisfies: -
space="preserve" listing-type="equation">0.4<
(r1a-r1b)/(r1a+r1b)<
2.5 (3)where r1a is the radius of curvature of a lens surface on the object side of said negative lens, and r1b is the radius of curvature of a lens surface on the image side of said negative lens. - View Dependent Claims (8, 9, 10, 11)
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12. A variable focal length optical system comprising, in succession from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,
wherein when a focal length of the entire lens system is changed while maintaining a constant image plane position, said second lens unit moves in an optical axis direction, said third lens unit moves in the optical axis direction to compensate for variations in image plane position upon movement of said second lens unit, and said first unit consists of only one negative lens element, said second lens unit consists of two positive lens elements, said third lens unit consists of a negative lens element and a positive lens unit which is positioned on the object side of the negative lens element, and said fourth lens unit consists of only one positive lens element.
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14. A variable focal length optical system comprising, in succession from an object side, a first lens unit (G1) having a negative refractive power, a second lens unit (G2) having a positive refractive power, a third lens unit (G3) having a negative refractive power, and a fourth lens unit (G4) having a positive refractive power,
wherein said first lens unit (G1) is fixed along an optical axis, and said second lens unit (G2) and said third lens unit (G3) move to the object side along the optical axis so as to decrease an air gap between said first lens unit (G1) and said second lens unit (G2), increase an air gap between said second lens unit (G2) and said third lens unit (G3), and increase an air gap between said third lens unit (G3) and said fourth lens unit (G4) when a focal length is changed from the shortest focal length state to the longest focal length state, and the entire lens system satisfies: -
space="preserve" listing-type="equation">0.6<
(β
2T/β
2W)/(ft/fw)<
0.95 (5)where β
2W is the lateral magnification of said second lens unit (G2) in the shortest local length state, β
2T is the lateral magnification of said second lens unit (G2) in the longest focal length state, fw is the focal length of the entire lens system in the shortest focal length state, and ft is the focal length of the entire lens system in the longest focal length state. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification