The SHARP II+ camera optics provides 3 different magnifications and a pupil imaging lens. The image scales and fields of view are summarized in table 2.1.
Table 2.1: Image scales and field of view
The optical design takes special care in the reduction of the
background by placing a Lyot-stop (special aperture stop with a central
obscuration to block radiation from the position of the telescope
secondary mirror) at an intermediate pupil position
within the camera. This intermediate pupil with a diameter of about 1.5 mm
is generated by a collimator made of Barium Fluoride and the Schott
IRG2 glass. Nearby this pupil position the different narrow- and
broad-band filters and the shutter are placed. The different doublets
mounted on the optics wheel behind the pupil provide the described
image scales. While the doublets for the 35 and 50 mas/pixel scale
are manufactured from Barium Fluoride only, the doublet for the 100
mas/pixel scale is achromatized like the collimator by a combination
of Barium Fluoride an IRG2.
Also mounted on this optic wheel, a doublet of two Zinc Selenide
lenses images the pupil on the detector. This pupil imaging optics
is used for the alignment of the camera to the optical axis of the
adaptive optics bench.
All the lens surfaces are coated
for maximum transmission in the wavelength range from 1.1 to 2.45 
. The overall transmission of the camera optics is about 10 % in
the wavelength range from 1.1 to 2.45 .