Soft focus lens system
AssigneeMinolta Camera Kabushiki Kaisha
InventorsYukio Okano, Akiyoshi Nakamura, Toshinobu Ogura
Life of this patent
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Abstract
A variable soft focus lens system particularly adapted for photography is provided. The soft focus lens system includes at least two lens groups defining a meniscus shaped air space there between. The relative width of the air space can be variable by movement of one of the lens groups relative to the other. This movement can introduce a controlled amount of spherical aberration to provide within certain parameters a soft focus image with an acceptable Petzval sum and flatness of the image plane. Various embodiments of the present invention within the inventive parameters can be utilized and include both stationary and variable soft focus lens system.
Claims22
A soft focus lens system having an optical axis and a point of intersection for an off-axial principal ray with the optical axis comprising:
- a first lens group of positive refractive power having a first image side refracting surface concave to the point of intersection, the point of intersection being located within the first lens group;
- and
- a second lens group of negative refractive power located at the image side of the first lens group and having a second object side refracting surface adjacent to the first image side refracting surface to form a meniscus-shaped air space between the first and second refractive surfaces, the radius of curvature, r.sub.A, of the first retracting surface and the radius of curvature, r.sub.B, of the second refracting surface having values defined within the following ranges, respectively, wherein the focal length of the lens system is represented by f:
- 0.20 <
- .vertline.r.sub.A .vertline./f <
- 0.65 (1)
- 0.18 <
- .vertline.r.sub.B .vertline./f <
- 0.45 (2)
- whereby an optimum degree of spherical aberration can be introduced into a transmitted image to provide a soft focus image.
A soft focus lens system having an optical axis and a point of intersection for an off-axial principal ray with the optical axis comprising:
- a firt lens group of positive refractive power having a first image side refracting surface concave to the point of intersection, the point of intersection being located within the first lens group;
- and
- a second lens group of negative refractive power movable relatively to the first lens group on the image side thereof and having a second object side refracting surface adjacent to the first refracting surface to form a variable meniscus-shaped air space between the first and second refractive surfaces for controlling the degree of spherical aberration introduced into the lens system.
An improved objective lens system having variable soft focus capability comprising:
- a first lens group;
- a second lens group adjacent to the first lens group;
- means for focusing the lens system on an object;
- varying means for varying the position of the first lens group relative to the position of the second lens group for controllably varying the amount of spherical aberration of the lens system to provide a soft focus image;
- and
- means, in automatic cooperation with the varying means, for maintaining the lens system focused on the object despite any variation of the position of the first lens group relative to the position of the second lens group during the controlled introduction of spherical aberration to provide the soft focus image.
A soft focus lens system having an optical axis defining a point of intersection for an off-axial principal ray within the lens system comprising:
- a first lens group including a first negative meniscus lens convex to the object side having an image side surface concave to the image side;
- a second lens group of a positive refractive power located at the image side of the first lens group including a second positive lens having an object side surface convex to the object side, a third biconcave lens, and a fourth positive lens having an image side surface convex to the image side, the point of intersection being between the third and fourth lens, the image side surface of the first negative meniscus lens having a radius of curvature, r.sub.B, the object side surface of the second positive lens having a radius of curvature, r.sub.A, to form a meniscus-shaped air space therebetween, wherein r.sub.B and r.sub.A fulfill the following conditions with the focal length of the lens system represented by f:
- 0.18 <
- .vertline.r.sub.B .vertline./f <
- 0.45
- 0.20 <
- .vertline.r.sub.A .vertline./f <
- 0.65.
Dependencies are inferred from the claim text.