Ricoh Company, Ltd.

Masami Itoh

Shuichi Kikuchi

Takao Yamaguchi

Noriyuki Iwata

Syuichi Kikuchi

A lens system includes a master lens system and a conversion lens system. The master lens system has a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of the lens system to an image side thereof, and has a first diaphragm which is arranged between the third lens and the fourth lens. The first lens is a positive meniscus lens having a convex surface toward the object side. The second lens is a negative lens. The third lens is a positive lens. The fourth lens is a negative meniscus lens having a concave surface toward the object side. The conversion lens system is arranged in such a manner that the conversion lens system can be freely inserted and removed between the third lens and the fourth lens of the master lens system. When the conversion lens system is inserted and removed between the third lens and the fourth lens, relative positions of the respective first, second, third and fourth lenses are fixed, and a focal length of the lens system becomes shorter than a focal length of the master lens system.

Lens system with master lens system and conversion lens

A zoom finder of a real image type has an objective lens having positive refracting power and an eyepiece having positive refracting power. The objective lens is constructed by first, second, third and fourth lens groups sequentially arranged from an object side. The first lens group has positive refracting power. The second lens group has negative refracting power. The third lens group has positive refracting power. The fourth lens group has positive refracting power. The zoom finder is constructed such that a real image is focused and formed by the objective lens between the fourth lens group and the eyepiece and is observed through the eyepiece. A magnification of the zoom finder is increased by moving the second lens group from the object side to an eyepiece side. A change in diopter caused by this increase in magnification is corrected by moving the fourth lens group. In accordance with the above structure, an entire length of the zoom finder is short and is not changed in a zooming operation. Further, the structure of a mechanical mechanism for displacing lenses in the zooming operation is simplified and no diopter of the zoom finder is changed in the zooming operation.

Zoom finder of real image type and real image type zoom finder capable

A compact zoom lens has first to fourth lens groups sequentially arranged from an object side. The first, second and fourth lens groups respectively have negative, positive and negative focal lengths. When a zooming operation is performed from a wide angle end to a telescopic end, a distance between the first and second lens groups is decreased, a distance between the second and third lens groups is increased, and a distance between the third and fourth lens groups is decreased. Focal lengths f.sub.1 and f.sub.2 of the first and second lens groups, focal lengths f.sub.2,3,4W and f.sub.2,3,4T of a combined lens system of the second, third and fourth lens groups at the wide angle end and the telescopic end, a focal length f.sub.3,4T of a combined lens system of the third and fourth lens groups at the telescopic end, focal lengths f.sub.W and f.sub.T of an entire lens system at the wide angle end and the telescopic end satisfy the following conditions where symbol .sqroot.[ ] means a square root of a value within bracket [ ].

Compact zoom lens

In a zoom lens having a high variable magnification, first and second lens groups and respectively having negative and positive focal lengths are sequentially arranged from an object side of the zoom lens to an image side thereof. A combined focal length of an entire lens system is charged by changing a distance between the first and second lens groups while the position of an image surface is constantly held. The zoom lens is constructed such that the second lens group is constructed by front and rear lens groups respectively having positive and negative focal lengths.

Zoom lens having high variable magnification

A compact zoom lens has a first lens group having a negative focal length f.sub.1 ; a second lens group having a positive focal length f.sub.2 ; and a third lens gorup having a negative focal length f.sub.3. The first, second and third lens groups are sequentially arranged from an object side of the zoom lens to an image side thereof. The first to third lens groups are moved on the object side while the mutual distances between the first, second and third lens groups are changed to perform a zooming operation from a wide angle side to a telescopic side. The third lens group is constructed by positive, negative and positive lenses sequentially arranged from the object side to the image side such that the negative and positive lenses respectively constituting the second and third lenses are joined to each other. The focal lengths f.sub.1, f.sub.2, f.sub.3 and a focal length f.sub.w of an entire lens system at a wide angle end of the zoom lens satisfy the following conditions.

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Higashikurume, Japan

Masami Itoh