Front conversion lens system

Claim 2

A front conversion lens system attachable only on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, the lens system satisfying the following condition: 0.25<(f/ΣDF) (L-L')/L<7.0 wherein; f represents a focal length of a photographing lens system including the front conversion lens system and the objective lens; ΣDF represents an axial thickness of the front conversion lens system; L represents a length of a diagonal line of an image plane to be printed when the real focal length photographing mode is selected; and L' represents a length of a diagonal line of an image plane to be printed when the pseudo focal length photographing mode is selected.

Claim 3

A front conversion lens system as claimed in claim 1, wherein the lens system includes from the object side at least one positive lens and at least one negative lens.

Claim 4

A front conversion lens system as claimed in claim 1, wherein the lens system includes, from the object side, a first positive meniscus lens element convex to the object side, and a second negative meniscus lens element convex to the object side.

Claim 5

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, the lens system satisfying the following condition: 0.25<(f/ΣDF)·(L-L')/L<7.0 wherein; f represents a focal length of a photographing lens system including the front conversion lens system and the objective lens; ΣDF represents an axial thickness of the front conversion lens system; L represents a length of a diagonal line of an image plane to be printed when the real focal length photographing mode is selected; L' represents a length of a diagonal line of an image plane to be printed when the pseudo focal length photographing mode is selected; the lens system including, from the object side, a first positive meniscus lens element convex to the object side, and a second negative meniscus lens element convex to the object side; and the lens system comprising the following design parameters: ______________________________________ Radius of Axial Refractive Abbe curvature distance index number ______________________________________ R.sub.1 25.836 D.sub.1 9.144 Nd.sub.1 .51680 νd.sub.1 64.2 R.sub.2 63.217 D.sub.2 11.886 R.sub.3 26.231 D.sub.3 7.354 Nd.sub.2 1.75690 νd.sub.2 31.8 R.sub.4 13.117 D.sub.4 3.000 ______________________________________

Claim 6

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, the lens system satisfying the following condition: 0.25<(f/ΣDF)·(L-L')/L<7.0 wherein; f represents a focal length of a photographing lens system including the front conversion lens system and the objective lens; ΣDF represents an axial thickness of the front conversion lens system; L represents a length of a diagonal line of an image plane to be printed when the real focal length photographing mode is selected; L' represents a length of a diagonal line of an image plane to be printed when the pseudo focal length photographing mode is selected; the lens system including, from the object side, a first positive meniscus lens element convex to the object side, and a second negative meniscus lens element convex to the object side; and the lens system comprising the following design parameters: ______________________________________ Radius of Axial Refractive Abbe curvature distance index number ______________________________________ R.sub.1 25.836 D.sub.1 9.144 Nd.sub.1 .51680 νd.sub.1 64.2 R.sub.2 63.217 D.sub.2 11.886 R.sub.3 26.231 D.sub.3 7.354 Nd.sub.2 1.75690 νd.sub.2 31.8 R.sub.4 13.117 D.sub.4 3.000 ______________________________________

Claim 7

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, the lens system satisfying the following condition: 0.25<(f/ΣDF)·(L-L')/L<7.0 wherein; f represents a focal length of a photographing lens system including the front conversion lens system and the objective lens; ΣDF represents an axial thickness of the front conversion lens system; L represents a length of a diagonal line of an image plane to be printed when the real focal length photographing mode is selected; L' represents a length of a diagonal line of an image plane to be printed when the pseudo focal length photographing mode is selected; the lens system including, from the object side, a first positive meniscus lens element convex to the object side, and a second negative meniscus lens element convex to the object side; and the lens system comprising the following design parameters: ______________________________________ Radius of Axial Refractive Abbe curvature distance index number ______________________________________ R.sub.1 26.119 D.sub.1 9.757 Nd.sub.1 .51680 νd.sub.1 64.2 R.sub.2 109.689 D.sub.2 12.572 R.sub.3 24.001 D.sub.3 8.254 Nd.sub.2 1.75520 νd.sub.2 27.5 R.sub.4 10.264 D.sub.4 3.000 ______________________________________

Claim 8

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, the lens system satisfying the following condition: 0.25<(f/ΣDF)·(L-L')/L<7.0 wherein; f represents a focal length of a photographing lens system including the front conversion lens system and the objective lens; ΣDF represents an axial thickness of the front conversion lens system; L represents a length of a diagonal line of an image plane to be printed when the real focal length photographing mode is selected; L' represents a length of a diagonal line of an image plane to be printed when the pseudo focal length photographing mode is selected; the lens system including, from the object side, a first positive meniscus lens element convex to the object side, and a second negative meniscus lens element convex to the object side; and the lens system comprising the following design parameters: ______________________________________ Radius of Axial Refractive Abbe curvature distance index number ______________________________________ R.sub.1 26.119 D.sub.1 9.757 Nd.sub.1 .51680 νd.sub.1 64.2 R.sub.2 109.689 D.sub.2 12.572 R.sub.3 24.001 D.sub.3 8.254 Nd.sub.2 1.75520 νd.sub.2 27.5 R.sub.4 10.264 D.sub.4 3.000 ______________________________________

Claim 9

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, comprising side: a first positive meniscus lens element convex to the object side; and a second negative meniscus lens element convex to the object side.

Claim 10

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which, an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, comprising side: a first positive meniscus lens element convex to the object side; and a second negative meniscus lens element convex to the object side.

Claim 11

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, said system comprising: a positive meniscus lens convex to the object side of the system; and a negative meniscus lens convex to the object side.

Claim 12

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, said system comprising: a positive meniscus lens convex to the object side of the system; and a negative meniscus lens convex to the object side.

Claim 13

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, said system comprising: a positive meniscus lens convex to the object side of the system; a negative meniscus lens convex to the object side; and said objective lens comprising, sequentially: a first positive meniscus lens element convex to the object side; a second bi-concave lens element; a third negative lens element; and a fourth bi-convex lens element adhered to said third negative lens element.

Claim 14

A front conversion lens system attachable on an object side of an objective lens of a camera in which either of a real focal length photographing mode and a pseudo focal length photographing mode in which an area, in an image recorded in a frame, smaller than a normal printing area printed when selecting the real focal length photographing mode is printed, is selectable, said system comprising: a positive meniscus lens convex to the object side of the system; a negative meniscus lens convex to the object side; and said objective lens comprising, sequentially: a first positive meniscus lens element convex to the object side; a second bi-concave lens element; a third negative lens element; and a fourth bi-convex lens element adhered to said third negative lens element.