This section describes how to focus the fiber spectrograph,
A&G Camera, and the telescope.
Telescope Focus :
Define a window in the AG control (),
of 50"X50" around a bright star in the field, and select a
short exposure time ()
Run the Focus script (). It will ask
a first focus guess, the number of guessed focuses to try (N),
and the increment of focus between them, using a prompt in
the IDL terminal.
Wait until the script has performed the N exposures and gives the
the best focus guess.
Change the nominal telescope focus if necessary.
Spectrograph Focus :
Select pics_GUI pull-down menu ()
Take a test exposure with calibration lamp (Neon, Hg, etc.)
with collimator and camera focus at best guess values
From within pics_GUI, inspect the frame for spots suitable
for focussing, use pull-down menu (),
(). The last selected window, before
quitting with the right mouse button, will be used subsequently
for window-readout during focus series.
Observe IDL command line; you are prompted for parameters
to run a focus sequence.
Start focus sequence. This operation will create a number of
window frames taken at various collimator and camera focus
settings, plus a listing of files resulting from the series.
Use spot_select.pro and pmas_spot to analyse the focus series
and determine best focus values for collimator and camera.
A&G Camera Focus :
Take a test exposure in full-frame mode near a best focus
guess (either with star simulator in storage room, or with a
real star at the telescope), to make sure that there is a
resonable signal.
Define window, centered on a sufficiently bright star.
Use pull-down menu ().
Observe IDL command line; you are prompted for parameters
to run a focus sequence.
Start focus sequence. This operation will create a number of
window frames taken at focus positions. The the FWHM values will
be evaluated, plotted, and fitted with a polynomial to derive
a best focus value.