Photographic lens system
AssigneeOlympus Optical Co., Ltd.
InventorsToshio Takahashi, Seiji Shimizu, Hideyasu Takato
Life of this patent
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Abstract
A photographic lens system which is composed, in order from the object side, of a first lens element having a positive refractive power, a second lens element having a negative refractive power, a third lens element having a positive refractive power, and a fourth lens element which has an aspherical surface on the image side and a negative refractive powers. An aperture stop is disposed between the second lens element and the third lens element or between the third lens element and the fourth lens element. This photographic lens system has a large aperture, favorable optical performance within a photographing range from infinite distance to an extremely short distance, a compact size and a simple composition, and can be manufactured at a low cost.
Claims25
A photographic lens system composed of four lens elements in order from an object side:
- a first lens element having a positive refractive power;
- a second lens element having a negative refractive power;
- an aperture stop;
- a third lens element having a positive refractive power;
- and
- a fourth lens element which has an aspherical surface on an image side and a negative refractive power,
- wherein said photographic lens system satisfies the following conditions (1), (2), (3) and (7'):
- 0.4<d.sub.6 /.SIGMA.d<0.6 (1)
- 1.4<-f.sub.4 /f<3.0 (2)
- 1.7<n.sub.3 <1.85 (3)
- 1.48<n.sub.2 <1.73 (7')
- wherein the reference symbol d.sub.6 represents an airspace reserved between said third lens element and said fourth lens element, the reference symbol .SIGMA.d designates a distance as measured from a first surface to a final surface of said lens system, the reference symbol f.sub.4 denotes a focal length of said fourth lens element, the reference symbol f represents a focal length of said photographic lens system as a whole, the reference symbol n.sub.3 designates a refractive index of the third lens element, and the reference symbol n.sub.2 represents a refractive index of said second lens element.
A photographic lens system composed of four lens elements in order from the object side:
- a first lens element having a positive refractive power;
- a second lens element having a negative refractive power;
- a third lens element having a positive refractive power;
- an aperture stop;
- and
- a fourth lens element which has an aspherical surface on the image side and a negative refractive power, wherein said photographic lens system satisfies the following conditions (1), (2) and (3-1):
- 0.4<d.sub.6 /.SIGMA.d<0.6 (1)
- 1.4<-f.sub.4 /f<3.0 (2)
- 1.48<n.sub.3 <1.7 (3-1)
- wherein the reference symbol d.sub.6 represents an airspace reserved between said third lens element and said fourth lens element, the reference symbol .SIGMA.d designates a distance as measured from a first surface to a final surface of said photographic lens system, the reference symbol f denotes a focal length of said fourth lens element, the reference symbol f represents a focal length of said photographic lens system as a whole and the reference symbol n.sub.3 designates a refractive index of the third lens element.
Dependencies are inferred from the claim text.