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US 5,687,027 AGranted
Zoom lens for optical apparatus such as camera
AssigneeCanon Kabushiki Kaisha
InventorYoshinori Itoh
Life of this patent
Estimating the term…
Abstract
To attain a compact wide-angle 2-unit zoom lens having a variable magnification range of 2.6 to 2.9 or thereabout which is well corrected for high optical performance throughout the entire variable magnification range with the total length shortened, the zoom lens comprises, in order from the object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, the separation between both the first and second lens units being varied to vary magnification, wherein an aspheric surface layer is formed on a lens surface of the object side among the lenses made of glass in the second lens unit by coating that lens surface with transparent resin and then setting the transparent resin.
Claims28
A zoom lens comprising:
- a first lens unit having a positive refractive power;
- and
- a second lens unit located on an image side of said first lens unit and having a negative refractive power,
- wherein magnification is varied by varying a separation between said first lens unit and said second lens unit, and
- wherein an aspheric surface layer made of resin and having an aspheric surface is formed on a surface of an object side of a glass lens of said second lens unit, and
- wherein said zoom lens satisfies the following condition:
- 3.times.10.sup.-4 <DA1/fT<2.times.10.sup.-3
- where DA1 is the axial thickness of said aspheric surface layer, and fT is the focal length at a telephoto end of the entire zoom lens.
5 more elements
A zoom lens comprising:
- a first lens unit having a positive refractive power;
- and
- a second lens unit located on an image side of said first lens unit and having a negative refractive power,
- wherein magnification is varied by varying a separation between said first lens unit and said second lens unit, and
- wherein an aspheric surface layer made of resin and having an aspheric surface is formed on a surface of an object side of a glass lens of said second lens unit,
- wherein said second lens unit comprises, in order from the object side, a first lens having a positive refractive power and a second lens having a negative refractive power, wherein said aspheric surface layer is formed on a surface of the object side of said first lens, and wherein the following conditions are satisfied:
- 10<.nu.A1-.nu.21<30
- 3.times.10.sup.-4 <DA1/fT<2.times.10.sup.-3
- where .nu.21 is the Abbe number of said first lens, .nu.A1 is the Abbe number of said aspheric surface layer, DA1 is the axial thickness of said aspheric surface layer, and fT is the focal length at a telephoto end of the entire zoom lens.
6 more elements
A zoom lens comprising:
- a first lens unit having a positive refractive power;
- and
- a second lens unit located on an image side of said first lens unit and having a negative refractive power,
- wherein magnification is varied by varying a separation between said first lens unit and said second lens unit, and
- wherein an aspheric surface layer made of resin and having an aspheric surface is formed on a surface of an object side of a glass lens of said second lens unit,
- wherein said second lens unit comprises, in order from the object side, a first lens having a positive refractive power and a second lens having a negative refractive power, wherein said aspheric surface layer is formed on a surface of the object side of said first lens, and wherein the following conditions are satisfied:
- 3.times.10.sup.-4 <DA1/fT<2.times.10.sup.-3
- 1.8<.beta.2T/.beta.2W<4
- where DA1 is the axial thickness of said aspheric surface layer, fT is the focal length at a telephoto end of the entire zoom lens, and .beta.2W and .beta.2T are the image forming magnifications for a wide-angle end and the telephoto end of said second lens unit, respectively.
6 more elements
A zoom lens comprising:
- a first lens unit having a positive refractive power and having, in order from an object side, a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the object side, and two positive lenses having respective convex surfaces facing an image side;
- and
- a second lens unit located on the image side of said first lens unit, having a negative refractive power and having, in order from the object side, a positive meniscus lens convex toward the image side and a negative meniscus lens convex toward the image side,
- wherein an aspheric surface layer made of resin and having an aspheric surface is formed on a surface of the object side of one of said positive meniscus lens and said negative meniscus lens,
- wherein magnification is varied by varying a separation between said first lens unit and said second lens unit, and
- wherein, letting the Abbe number of said positive meniscus lens be denoted by .nu.21, the Abbe number of said aspheric surface layer by .nu.A1, the axial thickness of said aspheric surface layer by DA1, the focal length at a telephoto end of the entire zoom lens by fT, and the image forming magnifications for a wide-angle end and the telephoto end of said second lens unit by .beta.2W and .beta.2T, respectively, the following conditions are satisfied:
- 10<.nu.A1-.nu.21<30
- 3.times.10.sup.-4 <DA1/fT<2.times.10.sup.-3
- 1.8<.beta.2T/.beta.2W<4.
6 more elements
An image forming optical system comprising:
- a first lens unit having a positive refractive power;
- and
- a second lens unit located on an image side of said first lens unit and having a negative refractive power,
- wherein an aspheric surface layer having an aspheric surface is formed on a surface of a certain lens of said optical system, and
- wherein said image forming optical system satisfies the following condition:
- 3.times.10.sup.-4 <DA1/fT<2.times.10.sup.-3
- where DA1 is the axial thickness of said aspheric surface layer, and fT is the focal length at a telephoto end of the entire image forming optical system.
4 more elements
Dependencies are inferred from the claim text.