3) optic axis光轴 a) optic axis光轴-- The direction at which a 78 68° beam transmitted through calcite without double 10 refraction called optic axis b) The optic axis is found by erecting a line at 78 either of the two corners 光轴 where three obtuse angles met(tte“ blunt” corners), making equal angles 680 with the crystal edges. Any line in the crystal parallel to this line is also an optic axis3）optic axis 光轴 78º 78º 68º 102º a）optic axis 光轴--- 光轴 The direction at which a beam transmitted through calcite without double refraction called optic axis. b) The optic axis is found by erecting a line at either of the two corners where three obtuse angles meet (the “blunt ” corners), making equal angles 68ºwith the crystal edges. Any line in the crystal parallel to this line is also an optic axis