Diffraction.

Scattering of light which occurs when light passes through a very small opening.

When a lens is stopped down to a very small aperture, therefore, diffraction increases and the image quality is reduced. Diffraction can also be used in a controlled fashion for lens construction. Canon have built very expensive but relatively lightweight lenses which use diffractive optic principles - their DO lenses.

Diffraction is a side-effect of the wave aspect of light. Really tiny apertures result in light interference - a kind of beat effect which results in light dark and areas.

cf. Airy disc, aperture, DO, f stop, light interference.

Entry last updated 2002-05-09. Term 343 of 1487.

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