Second-order imaging properties of circular field spectrographs.
The second-order focusing properties of a grating spectrograph with fixed entrance slit and a circular image field are investigated analytically. It is shown that the Rowland mount is the only circular field spectrograph mount which allows perfect tangential focusing (to second order) over a predetermined wavelength range, while two classes of mounts exist, one of which is nontrivial, for which astigmatism is corrected exactly on a circular arc.
Palmer
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