Optical Prisms
Prisms are solid glass optics that are ground and polished into geometrical and optically significant shapes. The angle, position, and number of surfaces help define the type and function. Prisms are blocks of optical glass with flat polished surfaces at precisely controlled angles to each other, each prism type has a specific angle that light path bends. Prisms are used to deflect, rotate, invert, disperse light or change the polarization of the incident beam. They are useful for folding optical systems or rotating images. Prisms can be used to invert and revert images depending on applications. SLR cameras and binoculars both use prisms to make sure the image you see at the same orientation as the object. One important thing to keep in mind when selecting a prism is that the beam reflects off multiple surfaces within the optic, this means the optical path length through the prism is much longer than what it would be within a mirror.
There are four main types of prisms based on different functions: dispersion prisms, deviation, or reflection prisms, rotation prisms, and displacement prisms. Deviation, displacement, and rotation prisms are common in imaging applications; dispersion prisms are strictly made for dispersing light, therefore not suitable for any application requiring quality images. Each prism type has a specific angle that the light path bends. One important thing to keep in mind when selecting a prism is that the beam reflects off multiple surfaces within the optic, this means the optical path length is much longer than what it would be with a mirror.
Dispersion Prisms
Prism dispersion is dependent upon the geometry of the prism and its index dispersion curve, based on the wavelength and index of refraction of the prism substrate. The angle of minimum deviation dictates the smallest angle between the incident ray and the transmitted rays. The green wavelength of light deviates more than red, and blue more than both red and green; red is commonly defined as 656.3nm, green as 587.6nm, and blue as 486.1nm.
Deviation, Rotation, and Displacement Prisms
Prisms that deviate the ray path, rotate the image, or simply displace the image from its original axis are helpful in many imaging systems. Ray deviations are usually done at angles of 45°, 60°, 90°, and 180°. This helps to condense system size or adjust the ray path without affecting the rest of the system setup. Rotation prisms, such as dove prisms, are used to rotate an image after it is inverted. Displacement prisms maintain the direction of the ray path, yet adjust its relation to the normal.
