Construction of a Nicol prism:

1.A calcite crystal whose length is 3 times as its width is taken.

2.The end faces of the crystal are  polished in such a way that the angles of the principal section become 68⁰  and 112⁰ instead of 71⁰ and 109 ⁰ due to increase the field of view.

3.The crystal is cut in to two pieces along the optic axis or perpendicular to the opposite faces PR and QS.

4.The two cut surfaces are polished and then cemented by Canada balsam.

5.The refractive index of Canada balsam is intermediate between the refractive index of ordinary ray and extraordinary ray for calcite.

  refractive index of ordinary ray             =1.658

  refractive index of Canada balsam        =1.55

  refractive index of extra ordinary ray   =1.486