A second advantage
is in simplicity and ease of assembly. A penta prism can be
placed into a single mount, whereas two mirrors would require
two separate mountings and a more complex procedure for assembly.
advantage to the prism lies in its size. A penta prism can
be easily manufactured with small dimensions and then simply
placed into an assembly. A miniature mirror system might require
special design for mountings and special tools for assembly.
The geometry of
reflection inherent in a penta prism deserves special note.
The 90°„ deviation, which is imparted to the incoming beam,
remains constant for different angles of incidence. This invariance
means that alignment of a penta prism is not critical in terms
of the deviation of a centerline through 90°„. Although this
invariance to alignment is shared by other prisms oriented
for two coplanar reflections, the penta prism is unique in
its ability to deviate the centerline by precisely 90°„. The
manufacturing tolerance of the 45°„ angle between the two reflecting
faces determines the accuracy of the centerline°Įs 90°„ deviation.