Nippon Kogaku K.k.

Nikon Corporation

Daijiro Fujie

Yutaka Ichihara

Koichi Wakamiya

Keiji Ohsawa

Yoichi Umegaki

An imaging optical system (10) having a focal length (f) and a maximum imagewise numerical aperture. The system combines diffractive and refractive optical elements such that aberrations, including axial chromatic aberration, are well-corrected over a large wavelength range from the visible into the infrared. The system comprises, objectwise to imagewise along an optical axis (A), a front lens group (G.sub.F) having at least one refractive optical element, a diffractive optical element (DOE) provided with a diffractive surface (D) having positive diffractive power and a focal length (f.sub.DOE). The system also includes a rear lens group (G.sub.R) having at least one refractive optical element. The system has an amount of spherical aberration at the maximum imagewise numerical aperture, is measured with respect to e-line wavelength light, in the limit as the positive diffractive power of the diffractive surface approaches zero, of RSA. The system also has a maximum amount of axial chromatic aberration of the imaging optical system over a wavelength range of 400-850 nm, as measured with respect to e-line reference wavelength light, of LA. Further, the following conditions, as well as several others, are preferably satisfied:

Imaging optical system

A Fresnel lens provided in the finder of a camera includes a central portion through which an optic axis passes, and a plurality of annular portions spaced apart from the central portion and disposed concentrically. The central portion and the plurality of annular portions have their respective focal lengths. The focal length of the central portion is shorter than the focal length of one of the annular portions which is remotest from the optic axis.

Fresnel lens in a finder optical system

A projection lens for projecting an image onto a screen includes, in succession from the screen side, a first lens component having a positive refractive power, a second lens component having a positive refractive power and whose both lens surfaces are convex surfaces, a third lens component of meniscus shape having its convex surface facing the screen side, and a fourth lens component having a negative refractive power and whose surface which is adjacent to the screen is a concave surface.

Projection lens

A rear conversion lens to be mounted in between an objective lens and a determined image plane to produce a composite focal length longer than the focal length of the objective lens itself comprises, in the order from the object side a first lens component, a second lens component and a third lens component. The first lens component has a positive focal length and the image-side lens surface being convex toward the image side. The second lens component has a negative focal length and the object-side lens surface being convex toward the image side. The third lens component has a negative focal length and is in the shape of a meniscus convex toward the image side.

Rear conversion lens

A retrofocus type wide angle lens has, in succession from the object side, a first component which is a positive meniscus lens having its convex surface facing the object side, a second component which is a negative meniscus lens having its convex surface facing the object side, a third component which is a negative meniscus lens having its convex surface facing the object side, a fourth component having a cemented surface of negative refractive power convex toward the object surface and having a negative refractive power as a whole, a fifth component which is a biconvex positive lens having a surface of sharper curvature on the object side, a sixth component which is a positive meniscus lens having its convex surface facing the image side, a stop, a seventh component which is a biconcave cemented negative lens comprising a positive meniscus lens having its convex surface facing the image side and a biconcave negative lens cemented thereto, an eighth component which is a positive meniscus lens having its convex surface facing the image side, and a ninth component which is a biconvex positive lens. The retrofocus type wide angle lens satisfies specified conditions.

Retrofocus type wide angle lens

A compact, large aperture ratio, long focus lens having a short total length includes, in succession from the object side, a first group comprising a positive meniscus lens having its convex surface facing the object side, a second group comprising a positive meniscus lens having its convex surface facing the object side, a third group comprising a negative meniscus lens consisting of a biconvex lens and a biconcave lens cemented thereto and having its convex surface facing the object side, a diaphragm, a fourth group comprising a meniscus lens consisting of a negative lens and a positive lens cemented thereto and having its convex surface facing the image side, and a fifth group comprising a positive lens.

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Sagamihara, Japan

Daijiro Fujie