focal lines

focal lines

[′fō·kəl ‚līnz]
(optics)
References in periodicals archive ?
through every point of F there pass infinitely many focal lines of B contained in F;
On the other hand, a parasitical component F is necessarily contained in L: if P [member of] F \ L, through P there passes a focal line l [subset] F, which is necessarily k-secant X, with k > N - 1.