R

Poisson's ratio v being imposed by the glass type, there is an infinity of pairs (b/a, n) that formally satisfy a Kerber profile. A search for pairs (b/a, n) giving these profiles has been carried out for 1/6 < v < 1/2, corresponding to most optical glasses. One notices that for n = 1, the surface area of the outer zone - which is not optically useful - is the largest. For n > 1, the area of the outer zone decreases. For large values of n, the plate thickness becomes too small for practicable applications. Thus, a fortiori, the compromise 3 < n < 6 has to be chosen for making large diameter correcting plates. The resulting determinations of the ratios b/a, as functions of n and v, are displayed by Table 5.1.

Table 5.1 Radius ratios b/a providing Kerber-profile plates of clear aperture 2rm = 2a as a function of loading ratio n and Poisson's ratio v

n

= q2/q\

0 0

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