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Chapter 5 - Optical Equipment

(Sample page excerpted from book)

Aspheric Lenses for Holography

Aspheric lenses have one or more surfaces which are shaped to a surface of revolution about the lens axis, including conic sections but excluding a sphere. Commonly used aspheric surfaces include paraboloids, hyperboloids, and ellipsoids, they differ from spherical lenses in that the radius of curvature varies from the lens axis to the edge. This causes incident light rays to bend by different amounts depending on what portion of the lens it enters.

This property is used to minimize or eliminate spherical aberration, which results when light

This chapter gives a short description of some optical equipment that may be of interest to holographers. First, information about aspheric lenses is presented. This is followed by a study that was done on the durability of various metals used to make pinholes. (Although it mainly deals with high powered lasers, the value of the study to holographers is that it presents the heat sink properties, reflectivity and melting temperatures of the metals used in pinhole manufacture.).

passing through different parts of a spherical lens focuses at different distances from the lens. The result is an image that is not as sharp as it would otherwise be. Spherical aberration is worst in fast optical systems, that is, where the diameter or aperture is large relative to the focal length. Hence, aspherics are effectively utilized in such systems.

Aspheric lenses are available in a wide range of diameters and focal lengths. Lenses as small as 1 to 2 mm diameter and focal length are used as laser diode collimators. At the other extreme, aspherics as a large as 16 inches in diameter are being used in holography. Materials can be either optical glass or plastic..

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