| 摘要 |
PURPOSE:To reduce the size of an automatic focus detector and to improve the precision by projecting and photodetecting luminous flux by the projecting means and photodetecting means of the automatic focus detector of a single-lens reflex camera through roof prism surfaces of a pentagonal prism. CONSTITUTION:Luminous flux L1 from a light source 15 passes through an area 11b on a roof surface of the pentagonal prism 11 and a cut area 12a of a focal plate 12 from a projection lens 16 and is deflected by a quick-return mirror 13 to illuminate a subject S through an area 14a of a photographic lens 14. Reflected luminous flux L3 from the subject S passes through another area 14b of the lens 14 and is deflected by the mirror 13 and then guided to a photodetection lens 18 and a photodetecting element 19 through the cut 12a and an area 11d of the other roof surface 11c of the prism 11. Whether the image on the photodetecting element 19 is in focus or not is detected from its position, and an unshown controller in a figure moves the lens 14 to put the image in focus when the image is out of focus. Consequently, trouble due to the crossing of the pieces L1 and L2 of luminous flux is prevented and the small-sized device is constituted without altering the structure of the single-lens reflex camera greatly. |
