WFCAM Secondary (M2) tilt alignment

WFCAM Secondary (M2) tilt alignment

M2 tilt setpoints

  • Move the telescope to zenith, or close by and run a focus measurement using the H-band filter. Determine whether the field has sufficient stars (preferably more than 15 per camera) and if not, find a place close by in the sky that does or use the sky-subtraction focus mode.
  • Once the telescope is focused, take three focus measurements at H and use the wfcam_tilt script to determine average E-W (V) and N-S (U) tilt values.
  • Assuming the numbers are > +/- 0.1 then the tilt setpoints need adjusting. As yourself (rather than “observer”), go to /jac_sw/itsroot/install/configs and edit the secondary_wfcam.cfg file. The lines you are looking for are:

          mcu:hex:u3:base = 4.70
     mcu:hex:v4:base = 4.80

  • Adjust the value of the former for N-S tilt and the latter for E-W tilt, save the file and type “pvload secondary_wfcam.cfg” (hit the position button on the MCU Engineering Interface Epics screen if necessary to ensure that the top-end has moved) and repeat steps 1 to 4 until both U and V tilts are close to zero.

NB. If tilts are positive, then the setpoints in the secondary_wfcam.cfg file need to be increased by approximately the value of the measured tilt.

M2 tilt correction

  • Move the telescope to approximately 3-hours east and dec +20. Run an H-band focus measurement and determine if the field has sufficient stars abd if not find a place close by that does or use the sky-subtraction focus mode.
  • Once the telescope is focused, take three focus measurements at H and use the wfcam_tilt script to determine the average V tilt value.
  • Assuming the number is > +/-0.1 then you need to adjust the tilt correction model. As yourself (rather than “observer”), go to /jac_sw/itsroot/install/configs and edit the secondary_wfcam.cfg file. The line you are looking for is:

          mcu:hex:v4_tilt:k1 = -0.3;

  • Adjust the value, save the file and type “pvload secondary_wfcam.cfg” (hit the position button on the MCU Engineering Interface Epics screen if necessary to ensure that the top-end has moved). Repeat the previous 4 steps until the V tilt is < +/-0.1
  • Now move the telescope to 3-hours west, dec +20 and repeat the above steps. This should be quick as if you have the V tilt correction done for zenith and 3-hours east, it should, by default, be correct for 3-hours west.
  • Move the telescope to an HA of zero and dec -30 and repeat the above steps. This time you need to change the value of:

          mcu:hex:u3_tilt:k1 = 0.311

  • Confirm the tilts measured at HA 0-hours and dec +50.

When you’re happy with the tilt setpoints and correction the secondary_wfcam.cfg file needs to be committed to CVS. Do this by typing:

cvs commit -m “<your comment here>” secondary_wfcam.cfg