Binoculars having objectives spaced apart at a fixed distance and adjustable eyepieces

Binoculars comprising:

• a pair of objective units for forming an image, said pair being separated with a fixed spacing;
• a pair of erecting prism units for transforming the image received from said pair of objective units to an erect image, each of said pair of erecting prism units comprising a Pechan roof prism having a roof face, a disparity of at least 3 mm existing between a luminous flux center incident on each of said pair of erecting prisms and an optical axis along which light exits from each of said pair of erecting prisms, each one of said pair of erecting prism units rotating around an optical axis of a corresponding one of said pair of objective units;
• a pair of eyepiece units receiving the erect image from said erecting prism units, respectively, each of said pair of eyepiece units being rotatable, with a corresponding one of said pair of erecting prism units, around an optical axis of a corresponding one of said pair of objective units;
• a pair of vertical-angle-variable prisms, each one of said pair of vertical-angle-variable prisms being disposed between an objective unit of said pair of objective units and a corresponding erecting prism unit of said pair of erecting prism units;
• a microcomputer;
• a pair of shake sensors, each comprising a gyrosensor comprising a pitch shake sensor and a yaw shake sensor, and each for detecting a deviation caused by shake and sending a signal indicative of the deviation to said microcomputer;
• a pair of prism vertical angle sensors, each for measuring a vertical angle of a corresponding one of said pair of vertical-angle-variable prisms;
• a pair of driving actuators, each for driving a corresponding one of said pair of vertical-angle-variable prisms in response to a signal from said microcomputer based on a computation by said microcomputer of a prism vertical angle of said pair of vertical-angle-variable prisms for correcting image deviation, wherein each driving actuator of said pair of driving actuators is controlled by said microcomputer to stop driving the corresponding one of said pair of vertical-angle-variable prisms when said prism vertical angle sensor measures a vertical angle coinciding with the correct prism vertical angle computed by said microcomputer;
• and
• a battery disposed between said pair of objective units for supplying power to said pair of driving actuators,
• wherein each erecting prism unit of said pair of erecting prism units comprises a Pechan roof prism, comprising an auxiliary prism and a Schmidt prism, a spacer, and only one elastic member, wherein said spacer is disposed between said auxiliary prism and said Schmidt prism and has a single bored hole so that said spacer does not block optical passages of said auxiliary prism and said Schmidt prism and so that said spacer does not contact total reflecting portions of said auxiliary prism and said Schmidt prism, and wherein said auxiliary prism is disposed to receive light from a corresponding one of said pair of objective units, and said Schmidt prism is disposed to receive light from said auxiliary prism and direct the light to a corresponding one of said pair of eyepiece units,
• wherein each of said auxiliary prism and said Schmidt prism are planar prisms, and wherein the disparity existing between a luminous flux center incident on each of said pair of erecting prisms and an optical axis along which light exits from each of said pair of erecting prisms is effected by varying dimensions of at least one of said auxiliary prism and said Schmidt prism,
• wherein said auxiliary prism includes a first face disposed perpendicular to the optical axis along which incident light travels, a second face tilting at 45 degrees with respect to the optical axis, and a third reflecting face tilting at 22.5 degrees with respect to the second face, and said Schmidt prism includes a first face disposed perpendicular to the optical axis of said auxiliary prism, a second face tilted at 45 degrees with respect to the first face, and a third face comprising a roof reflecting surface whose ridge forms an angle of 67.5 degrees with a ridge of the second face,
• wherein each of said pair of erecting prism units is secured in a respective prism casing by the respective only one elastic member, said elastic member having a plurality of claws that press said respective prism unit against lateral walls of the prism casing,
• wherein, for each of said pair of eyepiece units, the optical axis thereof matches the optical axis along which light exits from the corresponding one of said pair of erecting prism units,
• wherein a distance between optical axes of said pair of objective units is larger than a distance between the optical axes of said pair of eyepiece units when said pair of eyepiece units are rotated to a closest possible position to one another, and
• wherein said objective units do not rotate when adjusting the distance between optical axes of said pair of eyepiece units.