Focus detecting apparatus with both passive and active focus capability

摘要

A focus adjusting system is provided with both a passive AF capability wherein ambient light is utilized and an active AF capability wherein an LED element for projecting light off the optical axis of a photo-taking lens and light reflected from an object after having been projected by the LED element are utilized. The focus detecting apparatus includes a secondary image forming element and an aperture opening disposed in the vicinity of the secondary image forming element. The aperture opening is symmetrically positioned relative to the optical axis of the photo-taking lens and lies on a straight line which contains the optical axis of the photo-taking lens and which is perpendicular to a straight line connecting the optical axis of the photo-taking lens and a projecting light optical axis. The aperture opening has a pair of inner regions and a pair of outer regions. A first cut-off filter having a property of cutting off rays of light of a wave-length projected from the LED element is provided. First and second AF sensors are adapted to receive the light, which has passed through at least the pair of the outer regions of the aperture opening, and the light which has passed through the pair of the inner regions of the aperture opening, respectively. A second cut-off filter is also provided, having a property substantially identical with that of the first cut-off filter and disposed on the second AF sensor.