Theory of mirror spectographs. III. Focal surfaces and slit curvature of Ebert and Ebert-Fastie spectographs

Abstract

A sp ati al t h eo r y of the focal surfaces an d slit cur ves of EbcrL an e! EbcI'L-Fast ie mon ochrom atol's and sp cctrograph s is pl'csc n ted.In a scco nd-order a pprox im atio n, i t y i el d s close d expr ess ion s f or U1C' focal surface, from w hi ch a " sto p-shift " t heo r y is developed to st u dy t he influence o f Lh c posi t io n of t he grat i ng i n t he spectr og r aph upon th e curvat ure of t he spect r um. 1'1 1(' co nd it ion for an C'xtended fl at spectrum is deri vee! , and t h e Ebe r L-l cast ie sy stl' m is shown La b e t he p ref eriI,bl e on e fo r spectr ogr ap h design.T lw cllrvatu r e of l ong m onoc hrom ato r sli t s is al so de ri ved as a cl osed, seco nd-ord er C'xp J'('ss ion. Th e Eber sys tem, on ly , ca n be equ i pped with lo ng sl it s, so that it , in t urn , co n i i Lu Les Lhe super ior monoc hromato r m oun t in g.A fourLh-ol'e! er approxi maLion is also incl uded for sLill m o re acc u mLe comp u tations.

Far ultraviolet instrument technology

“…A photometer can also be used as the detection element in a spectrograph. One of the most commonly used spectrograph designs is the Ebert‐Fastie spectrometer [ Fastie , ; Mielenz , ] because it uses a plane grating. This design enables one to either record a spectrum (there is, of course, a temporal ambiguity due to the time it takes to make the series of measurements) or select a particular wavelength interval to study.…”