Finder optical system for single lens reflex photographic cameras

Claim 1

A finder optical system for single-lens reflex photographic cameras wherein an even number of at least four small reflecting surfaces are arranged on the front surface of a pentagonal prism, an optical information such as graduation on the diaphragm dial or shutter speed dial arranged on the diaphragm ring or shutter ring of the camera is reflected consecutively by said small reflecting surfaces so as to emerge from said pentagonal prism, whereby said optical information is visible at any optional position around the field of view in the finder, and wherein said reflecting surfaces consist of a first small reflecting surface, a second small reflecting surface, a third small reflecting surface and a fourth small reflecting surface, said first small reflecting surface functioning to reflect said optical information upward, said second small reflecting surface functioning to further reflect the optical information reflected by said first small reflecting surface in such a way that said optical information is directed upward along the front upper surface of said pentagonal prism, and said third and fourth small reflecting surfaces functioning to permit observing an image of the optical information from said second small reflecting surface at any desired position around the field of view in a finder.