Wavefront Aberration
Aberration has been used as a concept of "geometric optics" that takes light as rays since old times. Microscope optical systems which frequently handle a minute specimen in units of wavelength may use wave-optics analysis that also handles the phase of wave, taking light as "wave" including the effect of diffraction. "Wavefront aberration" is used as an evaluation method in this case. As shown in the figure below, if the ideal image-forming conditions are met in a microscope optical system, spherical wavefronts (spherical waves) emitted from a point on a specimen are converted to plane waves by an ideal objective lens. Plane waves are converted to spherical waves with an ideal tube lens, converging on a point on the image field. These wavefronts are called "ideal wavefronts".
Next, the behavior of a wave front in an optical system that actually possesses aberration is shown below based on the figure in section (1) Spherical aberration.
The deviation (degree of disagreement) between an ideal wavefront and an actual wavefront is known as "wavefront aberration".
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