Currently, two autoguider mechanisms are installed on the RCC telescope:
the same field what the main (1m) telescope is actually observing.
Both autoguider cameras can be controlled using the same type of script, however, the off-axis guider needs some tweaking and focusing before observations. The control scripts can be invoked from the
m5 computer, where these are named as
rcc-autoguide.qsifor the off-axis guider; and
rcc-autoguide.flifor the guider telescope guider.
Please note that the autoguider algorithms are rather sensitive to the roll of the respective cameras. Since both cameras are now attached via simple eyepiece support mounts, this roll can easily be misaligned (either unintentionally or deliberately). One must certainly take responsibility for any intentional aligning and/or (un)mounting of these cameras.
Usually the default options are adequate, therefore only running it without arguments should suffice. Otherwise, the exposure time and the relaxing time can be set with the following command:
$rcc-autoguide --exptime T --relax m
T and m are integers in seconds. Here, and in the following we refer the autoguide scripts as
$rcc-autoguide which can either be
rcc-autoguide.qsi if we are doing off-axis guiding or
rcc-autoguide.fli if we use the guider telescope and the FLI camera mounted on the guider telescope.
Before starting the autoguiding process, check the temperature of the respective guider camera. In case of off-axis guiding, please also check the guider X-stage as well as set the telescope focus approriately (see below for further details).
Basically, the autoguide process performs the following.
T) which is used as a reference throughout the autoguiding process.
T, the necessary autoguiding offset is obtained by computing the offset between this image and the reference image and then the telescope position is adjusted accordingly.
mseconds. This part is called relaxing, i.e. when the whole autoguiding subsystem does nothing, just simply waiting (and relaxing).
There are two algorithms available in the autoguiding scripts which compute the offset between the reference and the current image.
$rcc-autoguidescripts to use this mode.
--pointto use this mode.
The main difference of these two modes is the following. The fine matching algorithm expects that the difference between the current and the reference image is within a few arcseconds and the autoguiding process will completely fail if (due to some reason) the offset is too large. In the case of the point matching, this offset can be very large (even in the range of arcminutes), the algorithm is capable to recover and lock again the autoguiding. However, this robustness needs more reference stars as well...
The scripts print the number of stars found on the reference image and the current images as well as the match success ratio and the status of the autoguiding, so one can easily fine-tune the parameters.
In order to fine-tune on the autoguiding process, first, one can acquire a test image:
$rcc-autoguide --exptime T --output test.fits
Use the command line argument
--xpa to let the autoguider script display the acquired image automatically in a
Both the autoguiding process and this test image acquisition prints the CCD temperature. Use the command
$rcc-autoguide --temperature TEMP
to set the temperature to
TEMP degrees of Celsius. -30 degrees of Celsius are usually fine, but if the cooling power can be stabilized at a maximum of 80-90%, even colder CCD temperature setpoints can be used.
In order to efficiently use the off-axis guider, one has to ensure that the guider X-stage mechanism is centered. If unsure, first reset the X-stage with the command
Then, move it to the central position with the command
The first step (resetting) is neccessary if the spectrograph state is unknown or after a power loss. If the guider X-stage offset is reported to 58000 by the
acectrl --status command, one can almost be sure that the X-stage is centered. However, unintentional tampering of the X-stage motor moves the X-stage mechanism while the controller do not sense this motion (i.e. the reported guider X-stage offset won't be altered).
If the test images acquired by
rcc-autoguide.qsi is not in focus, use the
acectrl --guide-focus +S or
acectrl --guide-focus -S command in order to fine-tune in the focus of the off-axis mechanism. 1 step is close to 0.01mm motion in the main focal plane, so focusing in 50-100 step units might be efficient for an f/13.5 telescope. Note that the off-axis guider is quite sensitive to temperature variations.
The guider telescope does not need any fine-tuning. It is always (more or less) in focus. However, ensure with the
CCD> rcc guidercap open
that the cap of the guider telescope is opened.