Guider Acquisition Failures

If the telescope fails to acquire a target, this checklist should help diagnose the problem. To follow this recipe, have easily available the APF Telescope 1, 2 and 3 desktop. You will also need the APF Instrument 1 and 3 desktop. On at least one desktop, have a free xterminal running as user on mainz.

The schematic outline:

  1. check for clouds in the web camera
  2. slew to bright (2< V < 4) star
  3. wait for the telescope to track
  4. check mirror covers are open
  5. check that the dome shutter is open enough to see star
  6. check hatch is open
  7. check that the ADC is working
  8. check that the guider is at the right focus (4.85)
  9. make sure guide camera is exposing
  10. check the telescope pointing and home the telescope

Check the sky camera for clouds. Patchy clouds can make acquisition tricky.

Acquire a star

Try to acquire a bright star. The easiest way is to use the Skychart on the APF Telescope 2 desktop. Click on a star at a high elevation, around 70 or so degrees, and is bright, magnitude 2-6. If possible, have it away from any current clouds.

Telescope Tracking and Mirror Cover open

Once the APF Telescope GUI reports that the telescope is tracking, check for the star in the guider. Double check that the mirror covers are open. The small tab at the bottom right of the APF Telescope GUI should show a row blue light next to the word Open.

Is the Dome Shutter Open?

If no star still appears and it is clear, check that the shutters are open. Use the Dome GUI on APF Telescope 1. Click on the Shutters tab and read the values of the current position of the shutters. Make sure that the shutters are in a position that allows the star to be seen. Place the front shutter at 30 degrees and the rear at 120. The easiest way to do this is with the command shutters -f 30 -r 120 in an xterminal on mainz.

Is Hatch Open, is ADC Working and is the Guider Focused?

Next, move to the APF Instrument 1 desktop. Find the APF spectrograph motor control GUI. Check if the Hatch is open. If the Hatch is closed, click on the word Closed, select Open and place the green arrow or play button.

Check to see if the ADC is in the correct position. The ADC should be showing an angle that is the zenith distance of the star. The zenith distance is simply 90 minus the star’s elevation.

Below the ADC is the control for the Guider focus. That value should be 4.85.

If either the guider or the ADC show a red cross instead of a green check mark, they may not be actually servoing to the correct position. This easiest way to fix this is to issue the commands in the xterminal on mainz. For the ADC, modify -s apfmot adcmod=pos and for the guider, modify -s apfmot guidefocmod=pos.

Turn on the Guider

The camera needs to be enabled. In the xterminal window, type modify -s eosgcam genable=true

Make sure the guider is exposing. On the APF Instrument 3 desktop, check that the Camera state is Exposing. If the camera is not Exposing, click the word Enabled and select the Start Camera option. Then click the green arrow or play button. The command modify -s eosgcam gexpose=true also will work.

Check Telescope Pointing and Home

If none of the above works, that means that there is a clear light path to the guider. The next thing to check is the telescope pointing. On the APF Telescope 2 desktop, check TelescopeInterface Offset Control Tab. Make sure that all of the offsets are 0.

To home the telescope, either click the Home button on the TelescopeInterface or use the command slew --home. After homing the telescope, park the telescope with the Park buttong or slew --park.