Binocular stereo-microscope

Claim 1

A binocular stereo-microscope comprising a right and left objective, a right and left eyepiece, a right porro prism arranged between said right objective and right eyepiece and a left porro prism arranged between said left objective and left eyepiece, each of said right and left porro prisms having a first, second, third and fourth reflecting surfaces, both said first and fourth reflecting surfaces being at 45 degrees to the plane vertical to the optical axis of the rays reflected by said first reflecting surface, said binocular stereo-microscope being arranged so that rays from an object pass through said objective and are reflected by said first, second, third and fourth reflecting surfaces in this order and an image formed by said rays is observed through said eyepiece, and said four reflecting surfaces being arranged to satisfy the relation expressed by the following formula: sin β cos ω-cos β tan (β-ν)-tan α sin ω=0 [ω=ω.sub.1 +ω.sub.2 and ν=ω.sub.1 -ω.sub.2 ] ω=ω.sub.1 +ω.sub.2, ν=ω.sub.1 -ω.sub.2 ≠0, α≠0 and β≠0 wherein reference symbol ω 1 represents the angle between the plane vertical to the optical axis of said objective and the plane including the optical axis of the rays reflected by said second reflecting surface and directed toward said third reflecting surface, reference symbol ω 2 represents the angle between the plane vertical to the optical axis of the rays reflected by said second reflecting surface and directed toward said third reflecting surface and the plane including the optical axis of said eyepiece, reference symbol β represents the rotational angle of said porro prism in the clockwise direction from the plane including the optical axes of said objective and eyepieces around the optical axis of said objective, and reference symbol 2α represents the internal angle between said right and left objectives.