principal foci


principal foci
points of convergence of rays parallel with the principal axis of a lens, or system: in the eye (approx.) 18 mm from the anterior nodal point, and 24 mm from the posterior nodal point, and holding the ratio of the indices of air and vitreum.

Medical dictionary. 2011.

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  • Principal focus — Focus Fo cus (f[=o] k[u^]s), n.; pl. E. {Focuses} (f[=o] k[u^]s*[e^]z), L. {Foci} (f[=o] s[imac]). [L. focus hearth, fireplace; perh. akin to E. bake. Cf. {Curfew}, {Fuel}, {Fusil} the firearm.] 1. (Opt.) A point in which the rays of light meet,… …   The Collaborative International Dictionary of English

  • Foci — Focus Fo cus (f[=o] k[u^]s), n.; pl. E. {Focuses} (f[=o] k[u^]s*[e^]z), L. {Foci} (f[=o] s[imac]). [L. focus hearth, fireplace; perh. akin to E. bake. Cf. {Curfew}, {Fuel}, {Fusil} the firearm.] 1. (Opt.) A point in which the rays of light meet,… …   The Collaborative International Dictionary of English

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