Image stabilizing optical system having a variable prism

Claim 1

An image stabilizing lens system for an optical instrument with an image forming lens system therein comprising an afocal telescopic system section and a deflecting means arranged in this order from the front in front of said image forming lens system, said deflecting means having an entrance flat surface and an exit flat surface, one of said flat surfaces being stabilized by coupling a portion of said deflecting means with a stabilizer for maintaining said flat surface in fixed spatial alignment with an original line-of-sight of said optical instrument despite accidental motion of said instrument, the other of said flat surfaces being fixed to said optical instrument along the optical axis of the instrument, said deflecting means having a refractive index of less than 2, and, by defining the difference between the position of the optical axis of said instrument and the optical line-of-sight of said optical instrument created by an accidental motion as the value δ, said entrance and exit flat surface of said deflecting means for being oriented as a result of instrument motion so that a cross angle is formed by said entrance flat surface and said exit flat surface so as to refract a ray of light to the extent of the refracting angle δ (N - N'), said afocal telescopic system having an angular magnification M and a plus symbol is indicated when an erecting afocal telescopic system is used while a minus symbol is indicated at the employment of an inverting system to said afocal telescopic system, said afocal telescopic system satisfies the equation: M = ± (N - N') wherein N is the index of refraction of said deflecting means, wherein N' is the index of refraction of a medium in which the entire lens system is placed, wherein an angle formed by a ray of light emitted from the afocal telescopic system and the optical axis thereof is equal to the refracting angle of said deflecting means when said entire system is in said medium, and wherein the ray of light emitted from the deflecting means is always parallel with the optical axis.