Detachable viewfinder arrangement for use in a photographic camera

Claim 1

A detachable viewfinder arrangement for use in a photographic camera having a focusing screen optically associated with the optical system of said camera and a mounting opening on the top of said camera and immediately above said focusing screen, which comprises a main prism having an insight surface through which the line of sight of an observer is directed, reflecting surfaces directing a beam of light carrying the viewfinder image into the eye of the observer along said line of sight; a fixedly positioned auxiliary prism including a first element located adjacent said main prism and having a bottom portion and a second element having the bottom thereof adjacent the uppermost surface of said first element, said uppermost surface of said first element being flush with one surface of a pair of oppositely sloping surfaces which constitute the roof of said main prism; a semitransparent membrane plated on either the bottom of said second element or the uppermost surface of said first element; at least one entrance positioned above the uppermost surface of said second element and through which another beam of light carrying a foreign image enters on to said uppermost surface of said second element, said another beam after having entered said uppermost surface of said second element traveling in such a manner that it passes through said semitransparent membrane and is reflected by said bottom of said first element and then by said semitransparent membrane directing said another beam on to the main prism and then to the insight surface in a straight line to provide the foreign image in the field of view of the observer viewing said viewfinder image.