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WORKING WITH CRYOCAM
CRYOCAM
is a slow scan, cooled, CCD camera which digitizes images at the
output of the CCD and transfers the information to an 80486 (or higher)
based computer via the 16 bit ISA bus. The CCD is a 1024x1024 pixel SITe chip,
the pixel size is 24um, the total image area is therefore 24.6x24.6mm.
Field of view (FOV) and pixel scale
At CASS the WHT plate scale is 4.51"/mm, hence the chip provides a FOV
of 1.85'x1.85' in normal mode. The pixel scale is 0.10824 "/pixel.
In focus mode the FOV is 256 pixels squared or 27.7" squared on the sky.
Best settings
- use focus mode only for bright stars (pointing), continuous monitoring,
don't use exposure times smaller than 1 second, try using TV filters for very
bright objects
- retain histogram setting
- use binning 2x2 for much faster read out
- to get a faster readout it is also possible to change from 16 bits to
8 bits, losing range in the grey-scale
Neil recomends:
Cryocam Histogram look-up table: 5s exp in 2x2 binning has similar histo to
30s in non-binned: no need to adjust! Use binned to acquire (faster) and
unbinned to check slit pos (better detail).
Problems
- the field in focus mode is too small
- the rotator centre is too close to the edge in focus mode
- there is no control on gray-scale & contrast in focus mode
- using focus mode changes most of the other settings, the program must be
restarted in order to fix this
- there are options for windowing the chip, but at the moment the software
doesn't work; to change the window you need to edit a file and change the
values there
Improvements
- be able to window the CCD in any mode (normal, guide and focus), and zoom
the windowed CCD to fill the display
- be able to guide on a subsection (any of the fiducial fibres of AF2) of
the windowed CCD, while displaying all other fibres
- the control of contrast and gray scale through the histogram limits is not
practical and slow; IRAF uses the right mouse key to perform this function
- we need a mean of marking a position (or more) on the screen
- it would be nice to have a scaling rule to know distances at a glance
- be able to define a wait time between exposures in focus mode, this way
the image would continuously update without stressing the mechanical shutter
too much