Optical relay for a microscope and a back aperture viewer therefor

In a microscope having an observation system including in optical alignment along an axis, an objective, a telescope lens and an eyepiece, said objective having a back focal plane and said eyepiece having an image plane, a relay lens system to relay said back focal plane to an optically equivalent location in a station positioned between said objective and said telescope lens and an optical element at said station selectively positionable in said location for rendering said optical element operable in a manner equivalent to being positioned in said back focal plane, the improvement comprising a viewer selectively positionable on said axis between said station and said eyepiece for observing said optical element, an additional lens, said viewer including first means to deflect said axis to an alternate path passing through said additional lens, said lens being adapted to focus an image of said optical element in said eyepiece image plane, second means to deflect said alternate path after said lens along said axis and focusing means to move said additional lens axially along said alternate path.