The present invention relates to cameras and particularly to a light measuring device for a single lens reflex camera capable of performing TTL direct light measurement of a dark object. 
A light measuring system for a single lens reflex camera, in which the exposure is determined on the basis of the light reflected by a film surface or a shutter curtain, offers a number of advantages.  Such a system makes it possible to carry out real time light measurement of an object being photographed.  Various kinds of devices using this TTL direct light measuring system are known.  For example, as shown in FIG.  1, the bottom of a mirror box between the photographic lens 1 and the film surface 2 holds a light measuring lens 3 and a photo sensor 4 to sense the light scattered on the film surface.  However, the scattering characteristics of the film surface 2 are distributed as shown by dotted lines in FIG.  1.  Consequently, the photo sensing element 3 arranged at the lower part of the left side receives a larger light component reflected by the lower part 5 of the film surface 2 than by the upper part.  The lower part 5 of the film surface 2 corresponds to the upper part of the object, and, in general, the upper part of the object corresponds to the light portion of the object such as the sky or a lamp in a room.  Accordingly, the photo sensor receives more light from the upper part of the object than the lower part.  In order to compensate for this excessive light, one may attenuate the light from the lower part 5 of the film surface 4.  This attenuates the overall light and is disadvantageous for the measuring process.  Further, the conventional light sensing element 4 has a small sensing area and it is difficult to carry out a quick and precise light measurement of the object with dim light.