How do I calculate my working distance after my image is reflected from a right angle prism?

The distance through glass, such as that used to manufacture our Right Angle Prisms, relate to an equivalent distance through air via a simple equation. Take the distance traveled through glass (d) and multiple it be the refractive index of the glass (n_d) to get the equivalent distance through air, or Optical Path Length (OPL):

d x n_d = OPL