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Optical system for real image finder of camera folds optical path by use of reflective surfaces to achieve wide range of dioptric adjustment for user, whilst offering compact accommodation in thin casing
Optical system for real image finder of camera folds optical path by use of reflective surfaces to achieve wide range of dioptric adjustment for user, whilst offering compact accommodation in thin casing
The positive objective system is followed by a multiply-reflective image inverter for the ocular system. Two or more reflections from surfaces at right angles assist dioptric adjustment, with incoming and outgoing optical axes parallel with each other and orthogonal to the object-objective system (I) optical axis (OP1). Dioptric adjustment is achieved by movement of first and second reflective surfaces, such that the optical path length from an image plane of the objective system, to the ocular system (II), is variable. L1/L2 lies in the range 0.1-0.4. L1 is the parallel-projected spacing between the point at which the optical axis leaves the second reflective surface and the final surface of the ocular system. L2 is the parallel-projected spacing between the object-facing surface of the objective system, and the final surface of the ocular system.
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