The roof prism is a right angle prism whose hypotenuse has been replaced by two mutually perpendicular surfaces. The action of the roof surface is to increase the reflecting times from odd to even, but not change the optical axis direction. Roof prisms are suitable for applications that demand both right angle deflection and image erection. Therefore, it is often used in terrestrial telescopes, imaging systems, viewing systems and rangefinders.
Crown, Flint, UVFS
λ/4 @ 633nm
90° ± 3'
90% of central dimension
δ: roof angle error
D: clear aperture
m: fringe down through the roof line
β: angle between optical axis and vertical line of roof