Fuji Photo Optical Co., Ltd.

Yutaka Sakai

Yoshikazu Doi

Kazunori Ohno

Kenzo Sado

Kazunori Ohono

Takaaki Uchida

A finder optical system for a single-lens reflex camera has an eyepiece comprising in order from the viewing end thereof a negative lens consisting of a single negative lens or of a composite lens comprised of a positive lens and a negative lens, and a positive lens group consisting of two or more lens subgroups one of which constitutes a composite lens formed of a positive lens and a negative lens, wherein the overall length L and the focal length f of the eyepiece satisfy the relationship 0.65&lt;f/L&lt;0.9. The finder optical system is suitable for use in a single-lens reflex camera having a small picture size since it enables the focal length of the eyepiece to be kept short and the image magnification high even in the case where the overall length of the eyepiece is great.

Finder optical system

A compact wide angle zoom lens comprising front and rear lens groups which are moved in opposite directions along the optical axis of the lens system to vary the magnification. The front lens group comprises a concave meniscus lens, a concave lens and a concave lens and the rear lens group comprises a convex lens, a first convex meniscus lens, a concave lens and two convex meniscus lenses, in the order mentioned from the object side.

Wide angle zoom lens

A focussing apparatus for a camera, having an indicator for indicating the degree of blurring of an image produced by the taking lens, comprising a plano-concave lens and a plano-convex lens, of the same curvature, which accordingly have no refracting power when in contact with each other, disposed in the viewfinder's optical path. Signals from an object distance measuring means and a position detecting means for detecting the shifted position of the taking lens, are fed to a differential amplifier. The output of the differential amplifier, which corresponds to the degree of blurring of an image produced by the taking lens, causes the concave lens and/or the convex lens to shift so that the distance between these lenses is directly proportional to the degree of blurring and gives a visible indication of the same in the viewfinder.

Focussing apparatus having blurring indicator

A rear stop type lens with highly corrected comatic flare is constituted of one convex meniscus lens, two concave lenses and one biconvex lens arranged in the order mentioned from the object side.

Rear stop type lens system

A compact rear stop type zoom lens suitable for use with a camera having an electronically controlled shutter. The rear stop type zoom lens is comprised of two lens groups which effect variation in magnification when moved in opposite directions on the optical axis of the entire lens.

Rear stop type zoom lens

A zoom lens system consists of a front lens group A comprising a negative meniscus lens L1 convex to front (i.e. object side) and a positive lens L3 having the face of greater curvature faced to front, and a rear lens group B comprising a positive lens L4 having the face of greater curvature faced to front, a positive menisucs lens L5 convex to front, a negative lens L6 having the face of greater curvature faced to rear and a positive lens L7. The front and rear lens groups A and B are moved in the opposite directions along the optical axis thereof to vary the focal length thereof. The above zoom lens system satisfies the following conditions where the focal length of the front lens group A is fA, the radius of curvature of the concave face of the negative meniscus lens L1 is r2, the radius of curvature of the front face of the positive lens L3 is r5, the radius of curvature of the convex face of the positive meniscus lens L5is r9 , the radius of curvature of the rear face of the negative lens L6 is r12 and the Abbe dispersion number of the positive lens L3 is .nu.3; -2.3&lt;fA&lt;-1.5, 0.45&lt;r2&lt;0.65, 0.5&lt;r5&lt;1.0, 0.4&lt;r9&lt;0.6, 0.3&lt;r12&lt;0.55, .nu.3&lt;40.

Zoom lens system

An inverted telephoto lens having a super-wide angle of view is composed of a negative meniscus lens L1 convex to the front as numbered consecutively from front to rear, a biconvex lens L2, a negative meniscus lens L3 convex to the front, a cemented positive doublet of a negative lens L4 and a positive lens L5, a biconvex lens L6, a biconcave lens L7 the rear surface of which has radius of curvature greater than that of the front surface thereof, a positive meniscus lens L8 convex to the rear, and a positive lens L9 arranged in this order. The Abbe dispersion number of the biconvex lens L6 is more than 53 and less than 61. The difference between the Abbe number of the negative lens L4 and that of the positive lens L5 of the doublet is more than 10 and less than 16.

Inverted telephoto type super-wide angle lens

A negative meniscus lens, a biconvex lens, a cemented biconcave lens, a cemented positive meniscus lens, a positive meniscus lens, and a positive lens arranged from the front to rear in this order constitute a retrofocus lens having a large diameter and short length with reduced aberrations. The air separation between the first lens and the second lens is designed to be longer than 0.45f and shorter than 0.75f to make the overall length of the lens system small without extremely increasing the refractive power of the first lens. The ratio of the radius of curvature of the front face of the second lens to that of the rear face thereof is designed to be greater than 0.33 and less than 0.6 to compensate for the spherical aberration and coma due to the first lens. The cemented face of the cemented biconcave lens located behind the second lens is designed to be convex to the rear.

Retrofocus type lens

In a zoom lens system dividable into a zooming lens component which varies the magnification without moving the image plane and a relay lens component, at least a part of the relay lens component is made to have no power so that the axial movement thereof may not vary the focal length of the zoom lens system and is moved along the optical axis in association with the zooming lens component to compensate the fluctuation of aberration caused by the movement of the zooming lens component.

A retrofocus type lens system particularly useful for single lens reflex cameras. The back focal distance is 1.56 times as long as the effective focal length of the lens system and the angle of view is as large as 84.degree.. The aperture ratio is as large as F/2.8 and all aberrations are well corrected. The lens system comprises a positive meniscus lens L1, two negative meniscus lenses L2 and L3 convex to the front, a positive meniscus lens or plano-convex lens L4 convex to the rear, a biconvex lens L5, a cemented negative lens component consisting of a biconcave lens L6 and a positive meniscus lens L7, a positive meniscus lens L8 convex to the rear, and a positive lens L9.

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Omiya, Japan

Yutaka Sakai