Seidel theory

Seidel theory

[′zīd·əl ‚thē·ə·rē]
(optics)
A theory of aberrations in which the sine of the angle which a ray makes with the optical axis is approximated by the first two terms in the sine's Taylor expansion (the first- and third-order terms), rather than the first term alone, as in a first-order theory.
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