Coma | Coma

Key Words: chromatic aberration, Spherical aberration

Definition:An optical aberration that results in points of a specimen towards the image periphery becoming elongated and resembling a comet-tail in shape

TECHNOLOGY:

Comatic aberration results from differences in the refraction of light rays passing through the various parts of the microscope lens as the incident angle increases. It can also occur as a result of axial misalignment of optical surfaces. Microscope images with comatic aberration show comet-shaped details towards the periphery of the field of view. Comet 'tails' may point towards the center of the field-of-view or away from it depending on whether comatic aberration is positive or negative. Blur sometimes apparent near the edges of the tail is called 'comatic flare'. As with spherical aberration, correction can be achieved by eliminating marginal rays by restricting the aperture or by using multiple lens surfaces during manufacture. Plan apochromatic objectives are corrected for spherical, chromatic, astigmatic, comatic, distortion, and field curvature aberrations. They may contain as many as eighteen to twenty separate lens elements.

RECOMMENDED SYSTEM:

Nikon's CFI Plan Apochromat objectives are designed to correct all optical aberrations throughout the visible spectrum from violet to red, from center to edges across the entire 25mm field-of-view.