Background

This document describes the procedure for acquiring exposures to check the optical alignment of DEIMOS. This procedure establishes the alignment prior to removal of any DEIMOS optics and determinesthe change following re-intallation of optics.

Prerequsites

• DEIMOS should be moved to the appropriate rotator position for servicing. The position may depend on what is being serviced. For the tent mirror and other optics requiring internal access, the best position is ROTATVAL=-270.
• The 1200-line grating should be installed in position 3 to perform the full check.
• The OG550 filter should be installed.

Acquisition Procedure

Follow this procedure to take data either prior to or following servicing.

• Bring up all DEIMOS control software under the dmoseng account.
• Select the 1200-line grating.
• In a polo xterm, execute the command:

  	~/scripts/alignment_exposures

  This will take a series of 3 spectral-mode exposures with the science mosaic.
• Select the mirror.
• In a polo xterm, execute the command:

  	~/scripts/alignment_exposures

  This will take a series of 3 direct-mode exposures with the science mosaic and 3 with the FCS.

Analysis Procedure

Follow this procedure after servicing to determine the shift and rotation of the optics relative to the previous value.

• Log into an HQ machine as dmoseng.
• Go to directory /home/dmoseng/optics/tent_mirror/alignment
• Edit the script do_measure_spots, adding new lines to measure the desired images.
• Launch IDL with start.idl61
• Go to proper directory via:

  	cd,'/home/dmoseng/optics/tent_mirror/alignment'

• Measure spots via:

  IDL> .run do_measure_spots

• Edit the script do_compute_offset.pro and add lines as needed to compare images taken before and after servicing.
• Measure offsets via:

  IDL> .run do_compute_offset

  Results are printed both to the terminal and the logfile compute_offsets.log.
• If there were no relative shift or rotation between the image, one would find the measured parameters dx, dy, and angle were all zero. Note that:
  • Shifts of under 5 px are probably OK.
  • Shifts of 5-10 px may be OK, esp. in the Y direction.
  • Shifts of >10px in dx may be a problem.
  • Rotation of 0.01 px corresponds to 1.4 px over the 8192 px width of the mosaic.

Log

Date	Image	Detector	Grating	Comment
2005-Mar-17	d0317_0041.fits	Science	Mirror	Before TM removal
2005-Mar-30	d0330_0005.fits	Science	Mirror	After TM install
2005-Apr-14	d0414_0009.fits	Science	Mirror	Before TM removal

See Also

• Tent mirror removal procedure
• Tent mirror install procedure

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Last modified: Wed Apr 13 12:22:31 HST 2005