In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of reflection prism used in optical instruments to alter the orientation of an image. Image File history File links Porro-prism. ... Table of Opticks, 1728 Cyclopaedia Optics ( appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... Ignazio Porro was an Italian inventor of optical instruments. ... If a shaft of light entering a prism is sufficiently small such that the coloured edges meet, a spectrum results In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colours (colours of the rainbow). ... In common usage, an image (from Latin imago) or picture is an artifact that reproduces the likeness of some subject—usually a physical object or a person. ...

It consists of a block of glass shaped as a right geometric prism with right-angled triangular end faces. In operation, light enters the large rectagular face of the prism, undergoes total internal reflection twice from the sloped faces, and exits again through the large rectangular face. Because the light exits and enters the glass only at normal incidence, the prism is not dispersive. In geometry, an n-sided prism is a polyhedron made of an n-sided polygonal base, a translated copy, and n faces joining corresponding sides. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ... Dispersion of a light beam in a prism. ...

An image travelling through a Porro prism is rotated by 180° and exits in the opposite direction offset from its entrance point. Since the image is reflected twice, the handedness of the image is unchanged. Handedness is an attribute of human beings defined by their unequal distribution of fine motor skill between the left and right hands. ...

Porro prisms are most often used in pairs, forming a double Porro prism. A second prism, rotated 90° with respect to the first, is placed such that the beam will traverse both prisms. The net effect of the prism system is a beam parallel to but displaced from its original direction, with the image rotated 180°. As before, the handedness of the image is unchanged.

Double Porro prism systems are used in small optical telescopes to re-orient an inverted image (an arrangement is known as a image erection system), and especially in many binoculars where they both erect the image and provide a longer, folded distance between the objective lenses and the eyepieces. Image File history File links Double-porro-prism. ... An optical telescope is a telescope which is used to gather, and focus light, for directly viewing a magnified image, making a photograph, etc. ... Porro-prism binoculars with central focusing Binocular telescopes, or binoculars, (also known as field glasses) are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, one to be viewed through each of the users eyes to present the viewer...

Commonly, the two components of the double Porro system are cemented together, and the prisms may be truncated to save weight and size.

A single Porro prism is a type of roof prism, though it is not used in this way in binoculars. A pentaprism used in Single-lens reflex cameras; the lower right face is the roof. ...

A variation on the double Porro prism is the Porro-Abbe prism. A Porro-Abbe prism (sometimes called a Abbe-Porro prism), named for Ignazio Porro and Ernst Abbe, is a type of reflection prism used in some optical instruments to alter the orientation of an image. ...