Abstract: A display system for displaying information in the viewfinder of a camera, capable of displaying a positive pattern indicating a distance measuring area and a light measuring area on a transparent background so that a photographing field can be seen through the transparent background of the pattern. The display system comprises a liquid crystal display of a guest-host type disposed near the focal plane of the optical system of the viewfinder. The liquid crystal display comprises transparent electrodes provided with a pattern indicating distance measuring areas and light measuring areas, a liquid crystal of a cholesteric-nematic phase transition type having a negative anistropic dielectric property as host, and a dichroic coloring matter having an anisotropic light absorption property as guest. The pattern having a high opacity is displayed on a transparent background in the viewfinder in a satisfactory contrast to the background.

Abstract: A viewfinder optical system including an objective lens for forming an image of a subject, a rooflike reflecting portion for reflecting an incident bundle of rays so as to deflect the incident bundle of rays through 90.degree., which is provided between the objective lens and the image of the subject formed by the objective lens, a double reflecting portion for twice reflecting a bundle of rays reflected by the rooflike reflecting portion so as to deflect the bundle of rays through 270.degree. and an eyepiece for enlarging the image of the subject.

Abstract: A viewfinder optical system, separate from a photographing optical system, for picture taking. The viewfinder optical system includes an objective lens, an eyepiece, and a compensation lens. The compensation lens is capable of being positioned in an optical path of the viewfinder optical system at object distances closer than a predetermined distance for simultaneously compensating for any variance in parallax and diopter between the viewfinder optical system and the photographing optical system in the macro mode.

Abstract: The present invention provides a variable magnification viewfinder optical system, comprising from the object side: objective lens group of a positive refractive power, including a first lens unit of a negative refractive power and a second lens unit of a positive refractive power, said first and second lens units being shiftable along the optical axis of the optical system for changing the magnification of the optical system; condenser lens group of a positive refractive power; and eyepiece lens group of a negative refractive power; wherein the objective lens group forms a real image of an object and the real image can be observed through the eyepiece lens group; and wherein the optical system fulfills the following conditions;-0.09/mm<1/f.sub.1 <-0.03/mm0.04/mm<1/f.sub.2 <0.11/mm-0.1/mm<fe/(f.sub.1 .multidot.f.sub.2)<-0.035/mmwherein: f.sub.1 represents focal length of the first lens unit of the objective lens group in millimeters; f.sub.

Abstract: A focus condition detecting device which eliminates a wasteful operation thereof to obtain optical results of detection in a shortest period of time and wherein it can be discriminated correctly depending upon data read from a lens regarding an exit pupil of the lens whether or not detection of a focus condition is possible. The device comprises an optical means which forms a plurality of pairs of light images from beams of light from pairs of areas of an exit pupil plane of an interchangeable lens. Relative displacements between the light images are detected by a plurality of focus condition detecting means. Data regarding optical characteristics of the lens are read from the lens, and in accordance with the data thus read, those ones of the focus condition detecting means for which detection of a focus condition is possible are selected from an optical relationship between the optical means and the exit pupil of the lens.

Abstract: Brightness of a central area in a scene to be photographed and brightness of a peripheral area around the central area are measured, and the brightnesses of respective areas are outputted as first and second values. When the second value is larger than the first value, the first value is corrected by a value which has no relation with the respective measured values. Consequently, a proper controlling brightness value is provided for controlling the exposure.

Abstract: A display system for displaying information in the viewfinder of a camera, capable of displaying a positive pattern indicating a distance measuring area and a light measuring area on a transparent background so that a photographing field can be seen through the transparent background of the pattern. The display system comprises a liquid crystal display of a guest-host type disposed near the focal plane of the optical system of the viewfinder. The liquid crystal display comprises transparent electrodes provided with a pattern indicating distance measuring areas and light measuring areas, a liquid crystal of a cholestericnematic phase transition type having a negative anisotropic dielectric property as host, and a dichroic coloring matter having an anisotropic light absorption property as guest. The pattern having a high opacity is displayed on a transparent background in the viewfinder in a satisfactory contrast to the background.

Abstract: An exposure control device for a camera comprising;first means for measuring light from a central area of an object field, said first measuring means including a plurality of means for receiving light from different portions within the central area, respectively; second means for measuring light from a surrounding area other than the central area, the surrounding area being greater than each portion within the central area; means for selecting between a first exposure control mode and a second exposure control mode; and means for controlling exposure in accordance with one of said plurality of receiving means in said first exposure control mode, and in accordance with all of said plurality of receiving means and said second measuring means in said second exposure control mode.

Abstract: A finder optical system comprises a first reflecting surface disposed at an image side of an objective lens to reflect light flux passing through the objective lens obliquely upward on the exit pupil side, a roof surface consisting of two reflecting surfaces orthogonally intersecting each other which is disposed obliquely upward on the exit pupil side of the first reflecting surface to perform right-left inversion of the light flux reflected by the first reflecting surface and to reflect the light flux obliquely downward on the exit pupil side, and a second reflecting surface disposed obliquely downward on the exit pupil side of the roof surface to perform an up-down inversion of the light flux reflected obliquely downward on the exit pupil side by the roof surface and reflect the light flux toward an eyepiece, and wherein the finder optical system fulfills the following condition: 20.degree.<.theta.<40.degree. wherein, .theta.

Abstract: A light measuring device for an exposure measurement at open aperture, lens-interchangeable photographic camera of a type capable of measuring the brightness of a target object to be photographed through a photo-taking lens assembly for the determination of an exposure amount, which device comprises a reading circuit for reading, from an interchangeable lens assembly, data associated with an exit pupil of the interchangeable lens assembly and data associated with the full aperture value of the interchangeable lens assembly, and a correcting circuit for calculating a correction value for a measured light value on the basis of the data read out by the reading circuit, for the purpose of exposure correction.

Abstract: An exposure control device for a camera comprising; first means for measuring light from a central area of an object field, said first measuring means including a plurality of means for receiving light from different portions within the central area, respectively; second means for measuring light from a surrounding area other than the central area, the surrounding area being greater than each portion within the central area; means for selecting between a first exposure control mode and a second exposure control mode; and means for controlling exposure in accordance with one of said plurality of receiving means in said first exposure control mode, and in accordance with all of said plurality of receiving means and said second measuring means in said second exposure control mode.

Abstract: A finder optical system comprises from the object side an objective lens having a positive refractive power as a whole, a condenser lens arranged in the vicinity of an image plane of the objective lens, an eyepiece consisting of a single lens element and having a positive refractive power, and further comprises a prism installed between the condenser lens and the eyepiece to introduce light fluxes having been passed through the condenser lens into the eyepiece, and wherein the finder optical system fulfills the following conditions; .nu.<50, 15 mm<fe<50 mm, 0.7<L/fe <1, wherein, .nu. represents an Abbe number of the prism, fe represents a focal length of the eyepiece, and L represents an optical path length of the prism defined as a ratio of thickness of the prism to the refractive index thereof. Thereby, axial chromatic aberration can be corrected well, and additionally, a finder image with high mangification is obtainable.

Abstract: A focus detection apparatus for a camera comprising: a condensor lens being arranged close to or behind a predetermined focal plane of an objective lens of the camera. A pair of image separation members for separating the image of an object formed on the predetermined focal plane by use of light having been passed through said objective lens into two images which are arranged behind the condensor lens symmetrically with respect to the optical axis of the objective lens, wherein the correlation between the two images formed separately is measured in order to detect the focus condition of the objective lens; said image separating members including a mask members for projecting the exit pupil of the image separation members within an exit pupil of a cata-dioptric lens system as the objective lens.

Abstract: A focus condition detecting system for a cata-dioptric lens wherein it can be judged correctly whether or not detection of a focus condition is possible, and a cata-dioptric lens for use with the focus condition detecting system. The system comprises a focus condition detecting means for detecting a relative displacement between a pair of images of light formed by a pair of optical means from beams of light from a pair of different areas of a plane of an exit pupil of a cata-dioptric lens to detect a focus condition of the lens. Data regarding outer and inner radii of an exit pupil or some other peculiar data are fixedly stored in the lens. The data are successively forwarded to a camera body, and depending upon the data, it is judged whether optically accurate detection of a focus condition is possible from a combination of the optical means and the lens. When the judgment is affirmative, the detecting means is rendered operative.

Abstract: A focus condition detecting device which eliminates a wasteful operation thereof to obtain optical results of detection in a shortest period of time and wherein it can be discriminated correctly depending upon data read from a lens regarding an exit pupil of the lens whether or not detection of a focus condition is possible. The device comprises an optical means which forms a plurality of pairs of light images from beams of light from pairs of areas of an exit pupil plane of an interchangeable lens. Relative displacements between the light images are detected by a plurality of focus condition detecting means. Data regarding optical characteristics of the lens are read from the lens, and in accordance with the data thus read, those ones of the focus condition detecting means for which detection of a focus condition is possible are selected from an optical relationship between the optical means and the exit pupil of the lens.

Abstract: An exposure controlling system wherein functional restrictions are little even when a cata-dioptric lens is mounted as an interchangeable lens and also provide an interchangeable lens for such an exposure controlling system. The exposure controlling system comprises means for reading data regarding aperture values of an interchangeable lens from the lens, and a light measuring means. In response to outputs of the two means, a display means displays, when the lens is an ordinary lens, a combination of an aperture value and an exposure time to which the ordinary lens can be controlled to provide an appropriate exposure, and when the lens is a cata-dioptric lens, a fixed aperture value and an exposure time for the fixed aperture value of the cata-dioptric lens which time provides an appropriate exposure.

Abstract: A distance measuring and light measuring optical system which permits an automatic exposure camera to have a minimized number of windows for various optical systems and to be minimized in size and production cost. The optical system comprises an exposure setting light measuring optical system, and a mirror interposed obliquely in an optical axis of the exposure setting light measuring optical system. The mirror has a dielectric multi-layer film coated thereon for selectively reflecting light of a predetermined wavelength for measurement of a distance but transmitting light of any other wavelength therethrough.

Abstract: A contralight compensation exposure control system which determines as a contralight condition and fires a strobe when there is a difference between the output of a partial light measuring means for measuring the brightness of a portion of a scene to be photographed i.e. the brightness of the main object such as a person, and the output of an average light measuring means for measuring the brightness of comparatively large area of the scene i.e. the brightness of the subordinate object such as the background of the main object. The control circuit of the system inhibits the strobe firing and actuates an exposure compensation means to shift the controlled exposure to the overexposure side when a detecting means detect uncompletion of charging of the main capacitor for firing the strobe even if the contralight condition is detected.

Abstract: A light measuring device, for use in a camera having an objective lens, for measuring a brightness of a spot of an object, uses an autofocus detecting system which includes an array of light receiving elements for producing charges at a rate relative to an intensity of the light impinging thereon from the object, and a light receiver provided adjacent the light receiving element array for producing a photocurrent at an amount relative to an intensity of the light impinging thereon from said object. The charges produced from the light receiving elements are integrated in a plurality of charge accumulation portions, respectively, and the charges produced by the light receiver is integrated in a capacitor. A comparator is provided for for comparing the integrated charges with a predetermined level, and for producing a stop integration signal when the integrated charges reaches the predetermined level so as to stop the integration in the first integration means.

Abstract: An exposure control device for a camera comprising:first means for measuring light from a central area of an object field, said first measuring means including a plurality of means for receiving light from different portions within the central area, respectively; second means for measuring light from a surrounding area other than the central area, the surrounding area being greater than each portion within the central area; means for selecting between a first exposure control mode and a second exposure control mode; and means for controlling exposure in accordance with one of said plurality of receiving means in said first exposure control mode, and in accordance with all of said plurality of receiving means and said second measuring means in said second exposure control mode.