Exposure control device for cameras

#1. Field of the Invention

#The present invention relates to camera exposure control devices capable of measuring light reflected from the surfaces of a leading shutter curtain and a film for exposure control based on the light measurement, and more particularly to such exposure control devices which provide correction of the exposure control to account for the differences in reflectivity between the surface of the leading shutter curtain and the film surface.

#2. Description of the Prior Art

#The above and other objects and advantages of the present invention will become more apparent from the following description of preferred embodiments representing the best mode of carrying out the invention when taken in conjunction with the accompanying drawings, wherein

#FIG. 1 is a cross-sectional view of a camera incorporating an exposure control device of the present invention;

#FIG. 2 is a diagram showing the output variation of a light receiving element when the reflecting power of the surface of a film is higher than that of the surface of a leading shutter curtain;

#With reference to FIGS. 1 through 5, the following description pertains to the errors occurring when the reflecting power of a film surface is different from that of a leading shutter curtain surface.

#In FIG. 1 movable reflecting mirror 10 is shown in the picture taking position, and scene light passing through an objective lens of an exchangeable lens 4 mounted on camera body 2 is incident on film surface 6 for exposure. Photodiode 12 is located on the floor of a mirror box (not shown), and condenser lens 14 is disposed in front of photodiode 12 for concentrating light rays reflected from the surfaces of leading shutter curtain 8 and film 6 in the vicinity of the center of an exposure aperture of photodiode 12. It should be noted that, with movable reflecting mirror 10 lowered to an angle at 45.degree. relative to the horizontal plane, the scene light having passed through the objective lens is reflected upwards by movable reflecting mirror 10 to form an image on focusing plate 16, the image being observed from eyepiece 22 through condenser lens 18 and pentagonal roof prism 20 in a manner known to those skilled in the camera art.

#FIG. 2 is a diagram showing the output of photodiode 12 during a period from time O, at which leading shutter curtain 8 of a shutter starts traveling, to time A at which the leading shutter curtain completes traveling, when the reflecting power of film surface 6 is higher than that of leading shutter curtain surface 8. The ordinate represents the output of photodiode 12, and the abscissa represents time. With a center-weighted light measuring system, as in the embodiments of the present invention, immediately after the commencement of travel of the leading shutter curtain, photodiode 12 receives, for the most part, light reflected by the leading shutter curtain surface. Therefore, output j of photodiode 12 depends on the reflecting power of leading shutter curtain surface 8. When the leading shutter curtain thereafter travels to the vicinity of the center of the exposure aperture, photodiode 12 gradually receives the light reflected from film surface 6 more than that from the leading shutter curtain surface 8, thereby causing output j of photodiode 12 to gradually increase. When the leading shutter curtain travels further to reach the end of the exposure aperture, photodiode 12 receives only the light reflected from film surface 6, whereby output j of photodiode 12 depends on the reflecting power of film surface 6, representing a constant value which is higher than that immediately after the start of travel of the leading shutter curtain.