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- W2199455820 abstract "In Chap. 4 we considered criteria for the optical efficiency of telescopes. Following Dierickx, the effective diameter D eff of a telescope was defined by Eq. (4.33) as $$ {D_{eff}} = D{left( {{tau _t}{I_0}} right)^{frac{1}{2}}} $$(6.1)where D is the physical clear diameter, 10 the measure (CIR) of the optical quality and τ t the throughput of the total telescope system. The measure of optical efficiency E t is then $$ {E_t}{left( {{D_{eff}}/D} right)^2} = {tau _t}{I_0} = {T^2} $$(6.2)The quantities I 0 and τ t enter into this expression with equal weight: neglect of either implies throwing away optical efficiency. Since the medium surrounding the optical elements of a telescope is almost always air, having a path length which is small compared with that through the atmosphere, the quantity τ t is effectively determined by the reflectivity of the mirrors and the transmissivity of any refractive elements. For the latter, the loss per surface reflection is, at the worst, that given by the Fresnel law [(n — 1)/(n + 1)]2 or 4 % for n = 1.5. This can often be reduced by anti-reflection coating. Absorption is often a serious problem in the UV unless fused silica can be used but is otherwise usually a minor loss. The most serious source of reduction of τt is therefore the reflectivity of mirrors, above all if there are a significant number in the optical train." @default.
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- W2199455820 date "1999-01-01" @default.
- W2199455820 modified "2023-09-24" @default.
- W2199455820 title "Mirror Reflecting Coats: Production and Cleaning" @default.
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- W2199455820 doi "https://doi.org/10.1007/978-3-662-08488-5_6" @default.
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