Optical Aberrations of the Microscope

A modern microscope is a series of lenses arranged on-axis to give an image appropriate for viewing by eye or with a camera. Optical aberrations arise from the dioptric nature of how lenses work. This chapter discusses the nature and effects of these optical aberrations. Most aberrations are taken care of by the manufacturer when designing the objective and other optical components. Aberrations are grouped as on-axis or off-axis types. The three on-axis aberrations are spherical aberration, astigmatism and chromatic aberration. Off-axis aberrations - which have a greater potential effect in high numerical aperture objectives - are: coma, field curvature, astigmatism, distortion and lateral chromatic aberration. Star test can be employed to recognise spherical aberration. A knowledge of these inherent aberrations and how they are minimised helps formulate criteria for working with and choosing the objectives best suited to the imaging task.