Optical Aberrations

Section Overview:

An ideal microscope objective produces a symmetrical diffraction limited image of an Airy pattern from an infinitely small object point. The image plane is generally located at a fixed distance from the objective front lens in a medium of defined refractive index. Microscope objectives offered by the leading manufacturers have remarkably low degrees of aberrations and other imperfections, provided the appropriate objective is selected for the task and the objective is utilized properly in accordance with the manufacturer's recommendations. It should be emphasized that objective lenses are not made to be perfect from every standpoint, but are designed to meet certain specifications depending on their intended use, constraints on physical dimensions, and price ranges.

Objectives are made with differing degrees of optical correction for both monochromatic (spherical, astigmatism, coma, distortion) and polychromatic aberrations, field size and flatness, transmission wavelengths, freedom from fluorescence, birefringence and other factors contributing to background noise. Depending upon the degree of correction, objectives are generally classified as achromats, fluorites, and apochromats, with a plan designation added to lenses with low curvature of field and distortion. This section addresses some of the more common optical aberrations that are commonly found (and often corrected) in microscope objectives.

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Selected Literature References

Selected Literature References

Aberrations are divided into two main categories: errors that occur when polychromatic light (white light) is passed through a lens, and errors that are present when only a single wavelength (monochromatic) of light is utilized. The selected references listed in this section contain information about the cause and correction of the most common optical aberrations encountered with microscope and other lens systems. Bear in mind that the optical designer must correct for both polychromatic and monochromatic aberrations simultaneously in the production of well-corrected microscope objectives.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

H. Ernst Keller - Carl Zeiss Inc., One Zeiss Dr., Thornwood, NY, 10594.

Kenneth R. Spring - Scientific Consultant, Lusby, Maryland, 20657.

Brian O. Flynn, John C. Long, Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.