TEST the TElescope and STar Simulator for BUSCA

TEST - the TElescope and STar simulator for BUSCA

TEST has been designed by Jürgen Schmoll and Klaus Bagschik to analyse the optical performance of the BUSCA beam splitter, in particular the correction for astigmatism. The main goal was to produce at the output an f/8 beam with a large back focal distance of about 400mm where the whole beam splitter unit can be placed. The basic arrangement is that of two Newton type telescopes looking face to face.

TEST can be used in two modes

In the classical star test mode a 5um precision hole is imaged on to a CCD camera for a PSF analysis. The PSF has been measured in the direct undistorted beam, for the passage through a singel planoparallel plate and through a second correcting plate. The results show, that with the correcting plate the PSF FWHP is of the same order as the airy disk of the 2.2m telescope. Even in sub-arcsecond seeing conditions the BUSCA optics wouldn't have any effect on the image quality.
In the Hartmann mode a Hartmann aperture plate with 10x10 holes is placed between the two Newton telescopes. At the output the beam is collimated and imaged on the CCD. The Hartmann spot pattern is analysed in order to quantitatively determine the low order wavefront aberrations.