Telescope offsets

The telescope is capable of making relative offsets in X/Y or in RA/DEC. Note at this time the only way to make an absolute position of the tracker is to start a new trajectory. In addition, the probes could be moved independently in RA/DEC or absolute X/Y. Note at this time no relative moves can be made with the probes.

There is also the ability to move the telescope but keep the same guide stars. This requires the telescope to move one direction and the probes to move the other. Because the probes live in a small annulus about 0.04 degrees wide (from 0.14 to 0.18 in radius). Thus, moves larger than about 100" have an excellent chance of moving a probe into a software limit.

Here is an example of that coordinated move:

mgp -toff=1,-0.8
mgp -toff=BR for LRS2 B -> R mgp -radec -toff=-100.5,2 offset in arcseconds

Or using lower level commands:

syscmd -T 'offset_trajectory(dx_ang=-100.5, dy_ang=2, adjust_probes="true")' where the dx_ang and dy_ang are given in arcseconds.

Unrelated to the B->R offsets is the format below for offsets in RA and DEC

syscmd -T 'offset_trajectory(dra=0, ddec=35, adjust_probes="true")' where the dra and ddec are given in arcseconds.

This type of offset will move any probe that has been given instructions to be positions since the last time that the system was reset. That means that even if you are not interested in the WFS1 that was used several trajectories ago that it will be offset as well and may hit a software limit causing problems. To clear the history of commanded moves use the following command:

Command: syscmd -T 'pfip_clear_positions()'

Positioning with the guider fiducial

For small offsets it is always better to use fiducial offset on the guiders rather than probe motions. Here is an example of that:

syscmd -T 'Guider1_offset_fiducial ( dx_asec=0.289,dy_asec=0.026,compensate="true")'

OR making offsets with RA and DEC in arcseconds instead of x and y.

syscmd -T 'Guider2_offset_fiducial ( dra_asec=1.289,ddec_asec=5.026,compensate="true")'

the compensate flag will try to move the other probes to keep them in the same relative position. For many tests you might not have those set so you might just run with

syscmd -T 'Guider1_offset_fiducial ( dx_asec=0.289,dy_asec=0.026,compensate="false")'

which will only move the Guider 1 fiducial.

The sense of the signs is such that the fiducial moves in the opposite direction as the command and the IHMP moves in the requested direction. For example:

syscmd -T 'Guider2_offset_fiducial ( dra_asec=1.0,ddec_asec=5.0,compensate="true")'

will move the Guider2 fiducial 1 arcseond West and 5 arcseconds south (opposite of the request) and when the guider catches up it will make the IHMP move 1 arcsecond East and 5 arcseconds north (same as the request).

Positioning with the ACQ camera fiducial

If you need to offset the fiducial while guiding on the ACQ camera, use, for example:

syscmd -T 'ACQ_offset_fiducial ( dx_asec=5,dy_asec=0,compensate="false")'

Offsetting telescope and probes

As an example, here is how to move from the IHMP center to the CWFS:

Offset to CWFS using syscmd -T 'offset_trajectory(dx_ang=-5.1, dy_ang=-4.9, adjust_probes="true")'

Offsetting from the HPFACAM setup position to the DirectACAM setup position ("Regular" to "Direct")

If there are thin clouds or a target that is too faint to guide on the HPFACAM, you can revert to a "direct"(DirectACAM) setup without canceling and reloading the trajectory. After the HPFACAM guiding fails, follow these steps:

• De-activate guiding on the HPFACAM.
• Insert the ACQ camera mirror
• Guide on the target at the "regular" (HPFACAM) position on the ACQ camera
• Run mgp -foff RD to move the fiducial position to the "direct" (DirectACAM) position
• wait while the probes and telescope move appropriate
• Begin an ordinary "direct" (DirectACAM) setup at this point