Setting Up an Automated Focus Run

The first time an automated focus run is performed, an entire night's observing should be dedicated to the focus procedure. Starting early is important to get a large temperature range through the night. Follow-up focus runs should be performed when the nighttime temperature changes significantly, for greater coverage of the temperature domain.

Setting up a set of focus runs is easy in the scheduler:

1. Make sure a focus run item is defined in astrod.conf, as described in Section 4.4.1.

   There should be a trigger sequence of the following form:

   trigger              focus_run        foc        0        fr

2. Set the focus run parameters in astrod.conf, as described in Section 4.4.2.

   The configuration parameters foc_lim and foc_step determine the range and stepsize for the focus run. Be sure that foc_lim liberally covers both sides of focus (usually a range of 0.5 mm is necessary). A stepsize of 0.02 mm should be adequate.

3. Put the following schedule items in astrod.conf:

   sched focus_run "-t 4 -p 1 -u -17.0 -c 120 -l 85.0 -a 180.0 -e 2000.0 -M 45.0"

   sched focus_run "-t 4 -p 1 -u -17.0 -c 120 -l 65.0 -a 180.0 -e 2000.0 -M 45.0"

   sched focus_run "-t 4 -p 1 -u -17.0 -c 120 -l 45.0 -a 180.0 -e 2000.0 -M 45.0"

   sched focus_run "-t 4 -p 1 -u -17.0 -c 120 -l 35.0 -a 180.0 -e 2000.0 -M 45.0"

   sched focus_run "-t 4 -p 1 -u -17.0 -c 120 -l 25.0 -a 180.0 -e 2000.0 -M 45.0"

   By specifying azimuth (-a) and elevation (-l), we ensure that we fix the elevation (at the start of each run) through the night. Specific fields specified by RA/Dec would drift through the night, making the focus model calculation difficult.

   In this focus sequence, each elevation is run 4 times (-t 4) during the night at 2 hour intervals (-c 120). An elevation is skipped if the field is within ${45^\circ}$ of the moon position. The sequence is started when the sun is ${17^\circ}$ below the horizon.