Autocollimating compensator for controlling aspheric optical surfaces
  A compensator (null-corrector) for testing aspheric optical surfaces is proposed, which enables i) independent verification of optical elements and assembling of the compensator itself, and ii) ascertaining the compensator position in a control layout for a specified aspheric surface. The compensator consists of three spherical lenses made of the same glass. In this paper, the scope of the compensator expanded to a surface speed ~f/2.3; a conceptual example for a nominal primary of Hubble Space Telescope is given. The autocollimating design allows significant reducing difficulties associated with practical use of lens compensators. 
V.Yu.Terebizh
astro-ph.IM