Porro-Abbe prism is an isosceles right angled prism made of glass blocks, with the end plane facing the right angle.
In use, light enters from the large rectangular surface in a prism, undergoes two total reflections on the inclined plane, and then penetrates the original incident plane to emit.
Because light only enters and exits in a normal state, the prism does not experience dispersion.
Porro-Abbe prism are used, especially in many binoculars, to provide image reconstruction and longer optical path folding, effectively shortening the distance between the objective and eyepiece.
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