  The "Bonn University Simultaneous CAmera" (BUSCA) is a CCD camera system
which allows simultaneous direct imaging of the same sky area in four colors.
The optics are designed for an f/8 beam and four 4Kx4K CCDs with 15m pixels
covering a field of view of 12 arcmin x 12 arcmin at a 2m class telescope. In
September 1998 BUSCA has seen "First Light".
  The instrument is based on three dichroic beam splitters which separate
optical wavelength bands such (at 430nm, 540nm, 730nm) that standard
astronomical intermediate-band filter systems can be used. The dichroics are
made of plane-parallel glass plates mounted at an angle of 45 degrees.
Astigmatism in the transmitted beams (f/8) is completely cancelled by identical
plane-parallel glass plates of suitable orientation.
  BUSCA offers new perspectives in astronomical multicolor photometry: i) The
broadband spectral properties (e.g. color indices) of astronomical objects in
the optical can be determined with high reliability even in non-photometric
atmospheric conditions. ii) Precious observing time is used very efficiently.
iii) With the large field of view, extended objects like globular and open star
clusters or galaxies are covered in a single exposure. iv) Each exposure
results in a complete data set.
