There exists another nomograph for selecting optical material pairs for achromatic color correction and passive athermalization in a housing with a non zero coefficient of thermal expansion. Adding the housing CTE complicates this nomograph. If you are having difficulty understanding this please refer to the method, by Gibbons, that does not include the housing. Background To predict the thermal defocus of a lens floating in air: This method was pioneered in the 70s by the reference sited below (authors from Carl Zeiss). They do not use thermal V number, but the therm optic coefficient (although they use γ instead of β) How does this nomograph work? R. Kremer helped me decipher the nomograph.The slope between two optical pairs will be color corrected and passively athermal for a housing whose coefficient of thermal expansion matches the slope between the two material points. Example. Let us assume we have four optical materials: Rhino, Giraffe, Cheetah and Zebra. We plot them. Slope between pairs tell us housing CTE: Here is a quick diagram of the optical system:
Sources: "Design of athermal lens systems" H. Kohler and F. Strahle in Space Optics, B.J. Thompson and R.R. Shannon Editors, National academy of Sciences 1974...
"Use of Hybrids in the 3-5µm infrared band" P.J. Rogers in Current Developments in Optical Design and Engineering V,SPIE proceedings Vol 2540 |
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