Abstract: A zoom lens has, in succession from the object side, a first lens unit G1 having an object side surface for contact with water and having a meniscus shape having its convex surface facing the object side and having negative refracting power, a second lens unit G2 having at least two negative lenses and a positive meniscus lens having its convex surface facing the object side and having negative refracting power as a whole, and a third lens unit G3 having at least two positive lenses, a negative lens and two positive lenses disposed on the image side thereof and having positive refracting power as a whole. The first lens unit G1 is fixed relative to the image plane, the second lens unit G2 is moved from the object side toward the image side and the third lens unit G3 is moved from the image side toward the object side to thereby vary the focal length from the wide angle to the telephoto.

Abstract: In a phototaking lens with the focal length variable from a predetermined value at the wide-angle end position to another predetermined value at the telephoto end position, a part of lens elements constituting the phototaking lens is rendered movable relative to other lens components. There is provided means for converting the lens, by the relative movement of a part of the lens elements, to a panorama state with a focal length even shorter than that at the wide-angle end position. The phototaking lens is a zoom lens having a first lens group of a positive refractive power and a second lens group of a negative refractive power in the order from the object side, wherein the focal length is varied by a change in the distance between the first and second lens groups, and the panorama state is obtained by a relative movement of the first lens group relative to the second lens group.

Abstract: An illumination device of this invention includes a flash light source for radiating flash light, a reflector, arranged on a side opposite to an object with respect to the flash light source, for reflecting a light beam radiated from the flash light source, and a refractor for projecting a light beam directly radiated from the flash light source and a light beam reflected by the reflector toward the object. The refractor adopts a Fresnel lens having a rotation-symmetrical shape with respect to its lens optical axis, a surface, on the object side, of the Fresnel lens is a flat surface perpendicular to the lens optical axis, and the other surface of the Fresnel lens is a Fresnel surface. The optical axes of the flash light source and the reflector are coaxial with each other, and define the reference optical axis of the illumination device.

Abstract: A Keplerian zoom finder optical system has an objective lens comprising, in succession from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit of positive refractive power and having positive refractive power as a whole, and an eyepiece of positive refractive power for enlarging and observing the focus image of the objective lens therethrough. The air gap between the first lens unit and the second lens unit is varied to thereby vary finder magnification. The Keplerian zoom finder optical system satisfies a predetermined condition.

Abstract: An optical apparatus capable of a panoramic photographing includes a photographing lens, an auxiliary lens having positive refraction to convert its focal length synthesized with the photographing lens to a focal length shorter than the individual focal length of the photographing lens without changing the positions of an image formation, and an auxiliary lens supporting means which removably supports the auxiliary lens in the optical path between the photographing lens and the image-formation plane, and is constructed to perform easily a usual photographing individually with the photographing lens as well as a panoramic photographing with the installation of the auxiliary lens.

Abstract: In a finder optical system wherein a field frame and a field lens are placed near an objective lens and a real image plane made by the objective lens and a prism having a reflecting surface is disposed between the field frame and an eyepiece, a transmitting surface substantially perpendicular to the optical axis of reflected light reflected by the reflecting surface of the prism is provided on the reflecting surface of the prism or by cutting away the reflecting surface, and an information display system for displaying desired information through that transmitting surface is provided. The information display system is provided at a position optically symmetrical with the field frame.

Abstract: A rectangular prism includes an entrance surface for receiving light, an exit surface from which the light emerges, two reflecting surfaces orthogonal to each other for directing the light ray incident from the entrance surface to the exit surface, and a groove of V-shaped cross-section disposed in the boundary between the entrance surface and the exit surface.

Abstract: A Keplerian zoom finder system has sequentially from its object side an objective lens with positive refractive power, a field lens with positive refractive power arranged in the vicinity of the focus of the objective lens, and an ocular with positive refractive power for observing the object image by the objective lens in enlargement. In the finder system, the aforesaid objective lens has from its object side the first lens of a biconcave lens with a more enhanced concavity toward the object side and the second lens of a biconvex lens with an aspherical surface on the eye point side. The Keplerian zoom finder system thus structured is characterized in that its finder magnification is varied by varying the air spacing between the aforesaid first lens and second lens and the conditions are satisfied.

Abstract: There is provided a behind stop wide angle lens system which comprises a positive lens L.sub.1 formed by joining a negative meniscus lens L.sub.11 whose convex surface faces an object and a positive meniscus lens L.sub.12 whose convex surface similarly faces the object, a biconcave negative lens L.sub.2, a biconvex positive lens L.sub.3 and an aperture stop S, disposed in this order from the side of the object. The behind stop wide angle camera achieves a wider angle of view and has an excellent imaging performance in spite of a simple structure and a compact size thereof.

Abstract: A Keplerian zoom finder optical system includes an objective lens unit comprising a forward group having negative refractive power and a rearward groups having positive refractive power, the objective lens unit having positive refractive power as a whole and having the magnification changing function of changing the finder magnification by the spacing between the forward group and the rearward group being changed, an eyepiece unit having positive refractive power for enlarging and observing therethrough a spatial image formed by the objective lens unit, and an image erecting optical system for erecting an inverted spatial image formed by the objective lens unit. The forward group in the objective lens unit comprises a first lens having negative refractive power and a positive meniscus-shaped second lens having its convex surface facing the object side, and is designed to have negative refractive power as a whole.

Abstract: In a Keplerian zoom finder optical system including an objective lens unit having a magnification changing function and having positive refractive power, and an eyepiece unit having positive refractive power for enlarging and observing therethrough a real image formed by the objective lens unit, the objective lens unit has, in succession from the object side, a forward from the object side, a forward group comprising a negative first lens and a positive meniscus-shaped second lens having its convex surface facing the object side, and having negative refractive power as a whole, and a rearward group comprising a biconvex positive third lens and a positive meniscus-shaped fourth lens having its convex surface facing the image side, and having positive refractive power as a whole, the spacing between the forward group and the rearward group being changed to thereby accomplish finder magnification change. The objective lens unit is designed to satisfy the following conditions:-0.12<r.sub.7 /f.sub.4 <-0.

Abstract: A behind stop wide angle lens system comprises a negative meniscus lens L.sub.1 having a convex surface directed to the object, a positive meniscus lens L.sub.2 having a convex surface directed to the object, a double-side-concave negative lens L.sub.3 having both surfaces concaved, a double-side-convex positive lens L.sub.4 having both surfaces convexed, and a stop S. These lenses are arranged in the mentioned order from the end adjacent the object. The lenses satisfying the following conditions (1) to (4):-2.8f<f1<-1.3f (1)0.7f<f2<0.82f (2)1.5<r1/r2<2.3 (3)0.13<r3/r4<0.4 (4)wherein f represents the focal distance of the whole lens system, f1 represents the focal distance of the negative meniscus lens L.sub.1, f2 represents the focal distance of the positive meniscus lens L.sub.2, r1 and r2 respectively represent the radii of curvature of the object-side surface and the image-side surface of the negative meniscus lens L.sub.

Abstract: A compound zoom lens optical system includes a variable focal length photographing lens consisting of a first lens group having a positive refracting power, and a second lens group having a negative refracting power from an object side in turn. A conversion lens is separably added to an image side of the variable focal length photographing lens. The conversion lens is simultaneously movable along an optical axis to be interlocked with at least one of the first and second lens groups of the variable focal length photographing lens so as to change a synthesized focal length with said variable focal length photographing lens. The variable focal length photographing lens and the conversion lens satisfy the following conditions:-1.5<.PHI..sub.1 /.PHI..sub.2 <-0.8-1.1<.PHI..sub.1 /.PHI..sub.23 <-0.2where .PHI..sub.1 is the refracting power of the first lens group, .PHI..sub.2 is the refracting power of the second lens group, and .PHI..sub.

Abstract: A Keplerian finder optical system composed of, in succession from the object side, an objective lens of a positive refractive power, a field lens of a positive refractive power positioned in the vicinity of the focal plane of the objective lens, and an eyepiece lens for observing an image of the object formed on the focal plane of the objective lens, comprises a field diaphragm positioned in the vicinity of the focal plane of the objective lens, a first reflecting device with two reflecting faces positioned in the optical path between the objective lens and the field diaphragm, and second reflecting device with two other reflecting faces, positioned between the field diaphragm and the eyepiece lens.

Abstract: A variable focal length photo-taking optical system includes a photo-taking objective lens, and a conversion lens removably added to the photo-taking objective lens and relatively movable along the optic axis with at least some lens groups of the photo-taking objective lens to change the combined focal length of the photo-taking objective lens and the conversion lens.

Abstract: A Keplerian zoom finder optical system having a zoom power variable objective lens, the Keplerian zoom finder optical system comprising: a zoom objective lens including a first lens group having a negative refracting power and a second lens group including at least a positive meniscus lens whose convex surface faces an image and having a positive refracting power, the lens group being moved for the purpose of conducting the zoom power variation; and an ocular used for enlarging and observing the image formed by the zoom objective lens, wherein when a focal length of the first lens group is f.sub.1, a focal length of the second lens group is f.sub.2, and a curvature radius of the convex surface of the positive meniscus lens is r.sub.

Abstract: A rear conversion lens which is to be mounted between a main lens and a predetermined image plane for attaining a larger resultant focal distance than a focal distance of the main lens basically comprises, in the order taken from an object, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, and has a negative refractive power as a whole.The structure meets the following conditional formulas.0.5<f.sub.1 /.vertline.f.sub.RCL .vertline.<0.6, f.sub.RCL <0 (1)1.2<r.sub.2 /r.sub.3 <1.4 (2)where f.sub.RCL is a focal distance of the rear conversion lens, f.sub.1 is a focal distance of the first lens unit, r.sub.2 is a radius of curvature of the first lens unit facing an image, and r.sub.3 is a radius of curvature of the second lens unit facing an object.

Abstract: A photo-taking lens of a two-unit, five element construction for an underwater camera comprises, in succession from the object side, a fixed forward unit having a first element having a meniscus lens having its convex surface facing the object side and having a negative refractive power when the medium on the object side is water, and a rearward unit having a positive second element having a biconvex positive lens, a negative third element having a biconcave negative lens, a positive fourth element having a positive meniscus lens having its convex surface facing the image side, and a positive fifth element having a positive lens having its surface of sharper curvature facing the image side, and movable as a whole along the optic axis for focussing. The photo-taking lens satisfies the following condition:0.75f<r.sub.2 <2f,where f is the rearward focal length of the entire system during focusing at infinity when the medium on the object side is water, and r.sub.