In order to sample the high resolution images delivered by the Martini
Adaptive Optics system, a reflective
f-converter can be inserted upstream of the telescope focal plane to
produce image scales of 0.08 or 0.05 ''/pixel in WHIRCAM. The
f-converter consists of two 25 mm diameter gold-coated mirrors (M1 and
M2, see Figure 9) which are
used off-axis to convert the f/11 beam to f/33 or f/55 before entering the
WHIRCAM cryostat. Cold stops matched to the size of the telescope pupil
image formed inside the cryostat are installed in the rear filter wheel and
are automatically rotated into position when the f-converter is used to limit
the background emission, by choosing the relevant magnifier option in the
CONFIG file. The FWHM diffraction limit of the WHT at 2.2 
m is
0.13'', and the 0.05 arcsec/pixel scale is designed to sample the
diffraction-limited core of well-corrected K-band images. The instrument
field of view in this mode is 13 
13'' at 0.05 ''/pixel.
(Due to space contraints, the f-converter can't be used in direct
imaging mode.)
Figure 9: Martini and WHIRCAM setup at GHRIL (courtesy of Peter Doel).