Performance comparison of two Wolter Type II telescopes in the vacuum ultraviolet

The SERTS-A and SERTS-C solar telescopes are examples of Wolter Type II glancing incidence telescopes built for flight1,2 on sounding rockets to study active regions on the sun in the extreme ultraviolet wavelength range 24-45 nm. Improvements in computer-controlled polishing technology at GSFC have led to the SERTS-C telescope which has substantially improved throughput and angular resolution in that wavelength range over the earlier SERTS-A. While both telescopes are diffraction-limited in the visible, preventing an obvious selection of the better telescope for flight, laboratory results in the far ultraviolet were used to make the selection and flight data are shown to illuminate these advances.