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This ICL procedure prompts for all the parameters required
for the data acquisition process. These are:
- The IPCS resolution factor. This determines the spatial
resolution, and is equal to 1, 2, 4 or 8 (see section ?).
- The central row and column of the image on the CCD
camera. In other words, these are the cordinates
that the centre of the image would have if the resolution
factor were 1.
- The dimensions of the image in centroided pixels.
- The number of IPCS frames per etalon step. When using
the IPCS it is normal to scan through a datacube very rapidly
many times. At each position the detector is exposed
for a specified number of ICPS frame times. An IPCS
frame time is typically 10-20 millisecs. Each time
the etalon is stepped one IPCS frame is lost, hence in
order to keep overheads down, whilst still scanning
rapidly, this parameter is normally set to about 10.
- The number of etalon steps (i.e. the z dimension of the datacube)
This must be less than 255 if a single-sided ramp,
128 for a double-sided ramp (see below).
- The start position for the etalon scan. The etalon gap
is altered during an observation by applying an offset
to the Z servo channel. The start position specified
here is the Z offset
to be used for the first plane of the datacube. It is
not specified in physical units, but in 'microprocessor
units'
- The size of the etalon step. This is the amount by
which the Z offset (i.e. the etalon gap) is incremented
between successive
planes of the datacube. It is not specified in physical
units, but in 'microprocessor units'
- The type of ramp function used. It is possible to scan
the datacube in two different ways. If a single-sided ramp is
used then the datacube will be repeatedly scanned from 1 to n,
where n is the number of planes. If a double-sided ramp is
used then the datacube will be repeatedly scanned from 1 to n,
and then back down from n to 1.
- The frame number to be used for 2D images. During
the night it will be necessary to take 2D calibration
frames such as ring frames (see section 16.2).
The parameter specified here determines the Z offset
(i.e. etalon gap) to be used for 2D images. For example,
if this parameter equals 10, then 2D images will be taken
with the same etalon gap as plane number 10 in the
datacubes.