What is the difference between Porro Prisms and Roof Prisms?
Every binocular is composed of two optical systems paired together; one for the left eye and one for the right. Each of these contains two prisms which are position in one of two designs: Roof or Porro. Roof prisms are positioned very close together, so close that the ocular or eyepiece is positioned directly behind the objective lens. As a result a roof prism binocular is more compact and generally more durable than anequivalent porro prism binocular. Porro Prisms are positioned in such a way that the oculars or eyepieces are offset from the objective lenses (ie the objective lenses are much farther apart than the oculars).
