Details
The penta prism will neither invert nor reverse the image. Penta prisms are extremely useful in alignment systems as they define a right angle very precisely and independently of angle of incidence. Rays entering one face emerge from the adjacent face at precisely 90 deg after they have undergone two reflections inside the prism for a total of 270 deg. The penta prism acts as a turning mirror which is insensitive to alignment.
