Abstract:
A camera including: and an objective lens, a finder for observing an object image, an array of minute prisms for presenting a display of characters in a viewing area of the finder, a light source for illuminating the minute prisms, a reflector for directing a light beam from the light source to the minute prisms, and a provision for absorbing undesirable light arranged on the side portion of the finder to absorb that part of the light which has passed through the prisms which would otherwise be refracted in a predetermined direction by the minute prisms.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to cameras having an information mark display device and, more particularly, to the finder display of camera in which undesirable light is removed. 
     2. Description of the Related Art 
     In this kind of device, many methods have been proposed. For example, LEDs or like display elements are put in a portion of the space surrounding the pentagonal roof type prism, and light issuing from them is brought by transmission to the finder viewing area (Japanese Utility Model Publication No. Sho 62-41311). In another method, a diffraction grating is formed on the focusing screen. The LEDs are positioned to face one side of the focusing screen so that light issuing from them is conducted by total reflection to the diffraction grating, by which it is bent to the finder viewing area (Japanese Laid-Open Patent Application No. Sho 56-99332). However, these are to present the display outside the field of observation. 
     Therefore, as the display is illuminated by the light emitting element disposed on the side of the pentagonal prism, the length of optical path has to be corrected at the outside of the pentagonal prism so that the distance from the display to the eye is equal to the distance from the focusing screen to the eye. This causes the layout to be complicated and its scale to greatly increase. A different example from those described above is shown in U.S. Pat. No. 4,662,716 where the display is made to be presented in superimposing relation on the scene image. But, this has a problem of dimming the display. 
     In addition, in U.S. patent application Ser. No. 480,671 filed on Feb. 15, 1990 which issued as U.S. Pat. No. 5,053,803 on Oct. 1, 1991 there is proposed a device for displaying an image of characters in the field of observation in such a way that the characters in the form of minute refractors positioned at or near a predetermined focal plane of the image forming lens are selectively illuminated by the light reflected from the main mirror. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to reduce the flare produced in the image when a display is presented in the camera having the objective lens fixed or detachably mounted thereto. 
     In the &#39;803 U.S. patent application Ser. No. 480,671, the display element is illuminated by an oblique light beam. In application to some cameras, it has been found that part of the light beam appears as flare in the image. This flare is caused by undesirable light in such a way that a portion of the illuminating light which has not been refracted by the display element is reflected in the finder optical path. In addition, other undesirable light in an amount less than the above-described undesirable light is caused by a bundle of rays which passes through the reflector for directing the illuminating light to the display element and, after reflection from the support receptor for the reflector, returns back. FIG. 5 depicts this phenomenon, and its effect will be described later. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an optical sectional view of an embodiment according to the invention. 
     FIG. 2A is a perspective view as viewed from the upper side of constituent parts of the embodiment. 
     FIG. 2B is a cross-sectional view taken along the D--D line of FIG. 2A. 
     FIG. 3 is a fractional sectional view of another embodiment. 
     FIG. 4 is a fractional sectional view of a further embodiment 
     FIG. 5 is a diagram for explaining the problem of the conventional example. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a single-lens reflex camera employing one embodiment of the present invention. In the same figure, a lens mount 1 is used for attaching or detaching a photographic lens L to or from the camera body, but the photographic lens L may be fixedly secured thereto. A main mirror 2 is the so-called quick-return mirror disposed in front of a film plane 3. A plurality of prisms 4 are disposed in a row perpendicular to the drawing to conduct light from LEDs 10. A focusing screen 5, a roof type pentagonal prism 7, an image forming lens 8 for light measurement, a light sensor SPC and an eyepiece lens 9 are housed together with the parts 2 to 4 and 10 in a common casing of the camera body. 
     Light coming from an object to be photographed and entering through the photographic lens L is reflected from the main mirror 2 to form an image of the object on the focusing plane 5d (upper surface) of the focusing screen 5. The details of the focusing screen 5 will be described in connection with FIGS. 2A and 2B. In order to efficiently conduct the imaging light beam which is focused on the focusing plane 5d to an eye of the observer, the focusing screen 5 is provided with a Fresnel lens on the lower surface 5e thereof. With the help of this, the light beam diffused by the upper or mat surface of the focusing screen 5 is subjected to the reflecting actions of the roof type pentagonal prism 7 and then is enlarged by the eyepiece lens 9, reaching the observer&#39;s eye in the form of an erect non-reverse image. 
     The main mirror 2 is a half-transparency mirror having a reflectance of 60% over the entire area. The light emerging from the photographic lens L passes in a portion R 1  through a region A 1  of the main mirror 2 at 40%. The transmitted light beam R 2  is then reflected by a submirror 11 to photoelectric conversion means 12. In this instance, the photoelectric conversion means 12 is used for focus detection, constituting part of the known device for determining the degree of focus about a plurality of areas in the field of view separately from one another. The reflected 60% light from the main mirror 2 goes to the pentagonal prism 7. A light source for illumination, in this instance, comprises a plurality of LEDs 10 arranged in a row perpendicular to the drawing in correspondence to display marks to be described later. A light bundle R 0  issuing from the LED 10 enters the light conduction prism 4, then is reflected by surfaces 4a and 4b and then emerges as a light beam R 3  toward the main mirror 2 where it is reflected in a desired direction, becoming a light beam R 4  to be used for illuminating a respective region of the focusing screen 5. 
     The focusing screen 5 is of the form shown in FIG. 2A in perspective view as viewed from above and in FIG. 2B in sectional view in such a manner that the display elements and the ordinary focusing screen are made up as one unit. However, both may otherwise be made up in separately. 
     Display elements d 1  to d 3 , though depicted in part, are rectangular frames which are formed of minute prism arrays 5a, 5b and 5c, respectively, and are positioned in correspondence to the respective focus detecting areas for the photoelectric conversion means 12. It is to be noted that the display may be assigned to the areas for weighted light measurement of the light sensor SPC. The display marks may be of different shape from that shown. Each prism of the minute prism arrays 5a, 5b and 5c has its angle determined so as to refract the illuminating light beam R4 in the same direction as the finder observation light. The reflected illuminating light beam R4 when arriving at the focusing screen 5 illuminates the minute prism arrays 5a, 5b and 5c disposed on the upper surface 5d of the focusing screen 5 shown in FIG. 2A. As shown in FIG. 2B, the light beam R 4  is subjected to refraction by the minute prisms, and only a bundle R 6  of light rays which have passed through the minute prisms is collimated with the aforesaid object imaging light beam, so that they go to the observer&#39;s eye. Meanwhile, that part of the object image bearing beam which has passed through the minute prisms is refracted in a direction different from that to the observer&#39;s eye. Therefore, when the light sources 10 are not turned on, those portions of the image on the focusing screen 5 which are occupied by the minute prism arrays 5a, 5b and 5c look dark. This is useful to let the observer recognize where the focus detecting areas lie. If one of the light sources 10 is turned on, the corresponding frame becomes bright, serving the observer to confirm which one of the focus detecting areas is particularly selected to operate. 
     Since the illuminating light beam R 4 , however, does not exclusively illuminate the minute prism rays 5a, 5b and 5c alone, a bundle R 6  of light rays which pass through other than these portions directs itself to the front upper face B (the gable of the roof) and is reflected therefrom to migrate into the observation light beam, thus becoming a ghost or flare. 
     Accordingly, in this embodiment, the front upper face B of the pentagonal prism 7 is coated with a light absorbing black paint layer 14 to take up the light bundle R 6 . 
     Therefore, even when the light source 10 is turned on, the observer can enjoy clear observation of the field of view and the display frame at a high quality despite illumination of the latter. 
     Next, FIG. 5 is a sectional view in enlarged scale of an area A 2  of the main mirror 2 and a support member 13 for the main mirror 2 with the invention not yet applied thereto. 
     Part of the light beam R 3 , i.e., a light ray r 3 , is reflected 60% from the front surface of the main mirror 2. The reflected light r 4  goes to the minute prism arrays 5a, 5b and 5c forming the display mark on the focusing screen 5. 
     The transmitted light ray r 5  past the front surface of the main mirror 2 reaches the front surface 13b of the main mirror support member 13. Since the front surface 13b of the main mirror support member 13 is a rough surface of the as-manufactured state, light impinging on the front surface 13b scatters, and some of the scattered light rays r x  go to the finder on turning toward the eye of observer to become ghost or flare. 
     However, the ghost or flare caused by these light rays, because it is trifling, creates no problems in the cameras used by common people. Still, for professionals and high by skilled amateurs, improvements are desired. 
     For this purpose, a first method is to apply vacuum evaporation of metal to the area A 2  of the main mirror 2 so that the reflectance exceeds 60%. By employing this feature, the light that transmits the main mirror 2 decreases. Also, because the light returning from the front surface of the support member 13, too, becomes more difficult to transmit the main mirror 2, it is made possible to extremely reduce the undesirable light. Again, because the reflectance of the portion that the illuminating light strikes increases, the displayed character becomes brighter, providing an additional advantage of making it easier to see it. 
     FIG. 3 shows another method of removing the undesirable light, being a sectional view in enlarged scale of the area A 2  and its neighborhood of the main mirror 2. Of the light rays r 3  of part of the light beam R 3 , the ones which have passed through the main mirror 2, i.e., light rays r 5 , reach the main mirror support member 13, where they are caused to stray by concave and convex stripes perpendicular to the drawing formed in a band area 13a of the front surface 13b of the member 13, so that they do not run in the direction to the eye of the observer. 
     FIG. 4 is a partial sectional view in enlarged scale of the area A 2  and its neighborhood of the main mirror 2. 
     Part of the light beam R3, i.e., a light ray r 3 , is reflected 60% from the surface of the main mirror 2. The reflected light ray r 4  goes to the minute prism arrays 5a, 5b and 5c of the focusing screen 5. On the other hand, a light ray r 5  which has passed through the main mirror 2 is reflected from an area A 3  of the front surface 13b of the main mirror support member 13. Here, the area A 3  is formed by applying a polishing process, thus becoming like a mirror, or is subjected to metal deposition. Therefore, the light ray r 5  is reflected from the area A 3 , becoming a light ray r 6 , and passes through the interior of the mirror 2, becoming a light ray r 4  &#39; parallel with the reflected light ray r 4 , and goes to the focusing screen 5. The bundle R 4  of light rays going to the focusing screen 5 is refracted by the minute prism arrays 5a, 5b and 5c arranged on the upper surface 5d of the focusing screen 5 in the direction to the eye of the observer. Thus, a bright display in superimposed relation on the aforesaid object image reaches the eye of the observer. 
     On the other hand, either this area A 3  of the main mirror support member 13 or the back surface of the main mirror 2 may be coated with a light absorbing paint layer.