The optical reducer is mounted on the universal adapter of the prime focus,
which contains two movable bundles of fibers for the off-axis guiding, lamps
for the calibration of the wavelength scale (a He-Ne-Ar lamp) and for flat
fielding (a continuous spectrum lamp). The lamps are placed in an integrating
sphere providing uniform illumination of the field. The calibration beam forms
at the input of the reducer a beam of an aperture ratio of F/4 equivalent to
that of the telescope. Such a scheme of illumination with equal filling of the
output pupil in observations and calibration ensures the absence of shift
when measuring radial velocities.
View on adapter from the main mirror's side:
A digital USNO catalog is used for automatic search of the two guiding stars and for calculation of coordinates for both guiding probes. Here "1" and "2" are guide's fields, red square is a SCORPIO field-of view and blue line is a direction of the longslit.