This invention relates to a range detecting device which detects or measures a distance between an object and the device. Various types of range detecting devices for enabling automatic or semi-automatic focus adjustment of camera lenses are conventionally known, and they are generally classified as passive or active types. The passive type has merit in that the mechanism is simple, but it has a disadvantage in that range detection is difficult when the scene is dark.
However, the active type of detecting devices projects the light from the device toward the object, and the reflected light is sensed, so that the disadvantage of the passive type devices is not present in this type. A camera having this active type of a range detecting devices is disclosed in U.S. Pat. No. 3,443,502.
In cameras using active devices such as the type shown in U.S. Pat. No. 3,443,502, a light source emits a beam which is moved angularly to sweep the field of the camera lens. The angular motion of the beam is linked to and calibrated with concomitant motion of the lens-focus-adjustment. A sensor is positioned to receive light reflected from the object, and, upon receiving this reflected light, the displacement of the focus-adjustment is arrested, thus positioning and holding the camera lens at the correct range adjustment.
In range detecting devices of the active type mentioned above when the light sensor fully receives the reflected light from the object and produces a signal of high intensity, the camera lens is at the correct range adjustment, and when the light sensor does not receive the reflected light and produces a signal of low intensity, the camera lens is not at the correct range adjustment. Therefore, for increasing the accuracy of the range detection, it is desirable that the sensor have a small displacement from the position of the beam which produces a low output signal to the position of the beam which produces a high output signal, namely, that the intensity of the sensor output signal vary definitively from a low state to a high state while the beam emitted from the light source is angularly moving to sweep the field of the camera lens.
It has been also desired to increase the maximum detectable distance that the active type range detecting device may detect between the object and the device.