Focus detecting optical system

A focus detecting optical system comprising:

• an objective lens for forming an image of an object;
• at least one condenser lens, disposed behind a predetermined image plane of said objective lens, for converging light passed through said objective lens;
• at least one pair of image re-forming lenses, located behind said condenser lens, for re-forming a pair of secondary images of the image formed by said objective lens;
• at least one pair of rows of light receiving elements, arrayed in a single line behind and in alignment with said paired image re-forming lenses, for detecting said paired secondary images;
• and
• a light deflecting member, disposed between said image re-forming lenses and said element rows and separated from said image re-forming lenses by an air space, for deflecting light fluxes forming said secondary images outwards in a direction of array of said element rows with respect to a center of said paired secondary images,
• said condenser lens, said paired image re-forming lenses, said paired element rows and said light deflecting member constituting one focus detecting assembly for detecting a state of focus adjustment of said objective lens on the basis of a change of the position of said secondary images detected by said element rows.