The previous paper ( Wm. G. FastieJ. Opt. Soc. Am. 42, 641 ( 1952)) described a plane grating monochromator optical system which apparently has not been used since Ebert described it in 1889. The high resolution obtained has inspired the design of an f/6 spectrometer of that type for the infrared region. This paper describes the results of preliminary tests and calculations which show that the Ebert system is capable of near theoretical resolution at f/6 even when very long slits are used. Both slits must be curved in order to remove the effect of astigmatism and to avoid wavelength errors at the exit slit which arise from curvature of spectrum when a plane grating is employed. That the same curvature of slits simultaneously corrects these two image errors is a fortunate coincidence which makes the Ebert system appear to be superior to currently employed spectrometer optical systems. Comparison with other systems and discussion of the limitations of the Ebert system are presented.
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