Auto-focusing apparatus

An auto-focusing apparatus comprising:

• photo-electric conversion means having a plurality of photo-sensing elements for sensing a light beam from an object directed through a focus detection optical system to produce object image signals representing light intensities of the photosensing elements;
• focus detection means for calculating a defocusing amount representing a focus adjustment status of a photographing optical system in accordance with the object image signals;
• drive means for driving said photographing optical system in accordance with the defocusing amount;
• control means for calculating the defocusing amount by said focus detection means in accordance with the object image signals when the object image signals of the photo-sensing elements are at a proper input level of said focus detection means to assure correct focus detection and driving said photographing optical system by said drive means in accordance with the calculated defocusing amount;
• and
• averaging means for calculating a mean value of the object image signals of at least a portion of the photo-sensitive elements,
• said control means calculating the defocusing amount by said focus detection means in accordance with the object image signals when the mean value calculated by said averaging means is smaller than a predetermined value even if a portion of the object image signals of the photo-sensing elements exceeds the proper input level of said focus detection means and driving said photographing optical system by said drive means in accordance with the calculated defocusing amount.