Summary

The AUTOPANE keyword allows DEIMOS to adjust the CCD readout window automatically to exclude unilluminated rows in the direct images and unnecessary rows in mask alignment images, thus saving readout time and disk space. This document describes the procedure for calibrating the operation of the keyword.

Implementation

The AUTOPANE system is imlemented using a shell script, the source code for which lives in deimosbuild at: 

/kroot/src/kss/deimos/fiord/deiccd/watch_pane
This script is invoked from the fiord output routine (output_expose) in the libdeiccd_keyword.so library whenever the EXPOSE keyword is written. In the current implementation of output_expose, watch_pane will only be invoked if mode is > 0.

The watch_pane script must be updated for each combination of grating and slider. The procedure for measuring the optimal direct imaging readout window and updating the watch_pane script involves the following steps. Note: this procedure is to be run by the staff astronomer, not the observer!

Prerequisites

  1. DEIMOS software running
  2. xterm window as dmoseng on polo for running commands
  3. editor window as dmosbld on deimosbuild for editing the script

Procedure

  1. Have summit staff configure DEIMOS as needed with the desired gratings in the desired sliders.
  2. Start DEIMOS software.
    1. Open VNCs for the dmoseng or any DEIMOS numbered account
    2. On the VNC pulldown menu: DEIMOS Control Menu → Start All DEIMOS GUIs
    3. Open the file watch_pane in your favorite editor in a deimosbuild terminal as dmosbld.
  3. Select grating/slider combination to calibrate (e.g., 900ZD in slider 4). NOTE: all grating/slider combinations are referenced to the mirror, so if the position of the mirror or of key optics has been disturbed (e.g., collimator moved), then begin by calibrating the mirror.
  4. Make sure that DEIMOS can be rotated.
  5. Execute the command take_autopane_image. This script then:
    1. Executes the gozero command to send the current grating to the Zeroth_Order position.
    2. Executes the fcszero command to reset the FCS system.
    3. Configures DEIMOS as follows:
      • hatch = Closed
      • slitmask = None
      • filter = R
      • readout = Direct
      • obstype = IntFlat
      • exptime = 4
      • autopane = FullFrame
    4. Takes a direct image using the configuration defined above. It should produce an image which clearly shows the outline of the slitmask form.
    5. Prompts you to inspect the image with ds9 (ds9 → Open as → Mosaic WCS...) to determine the FIRST and LAST illuminated rows in the image. Measure these as follows (best option is to use Edit → Crosshair):
      • The first illuminated row usually occurs in the lower left of the image. Set ds9 to zoom factor 1 and select a column in which to measure the rolloff. In this column, move up and down using the arrow keys and check the counts in each pixel. Locate the pixel where the flux is roughly halfway between the "background" level in the unilluminated regions of the image and the "plateau" in the illuminated region. Record the Y (CCD ROW) pixel (PANE) coordinate for this pixel. Enter this value at the script's prompt for the starting row.
      • The last illuminated image occurs in the upper right of the image. Zoom in here, select an appropriate column, and locate the point at which the intensity falls off by half. Record the Y (CCD ROW) pixel (PANE) coordinate for this pixel. Enter this value at the script's prompt for the ending row.
    6. Windows the CCD to the region you specified and acquires an image. Check this image to ensure that the readout begins about 40 rows before the first illuminated row and ends 40 rows after the last illuminated row. If not, then re-run the script and re-measure the starting and ending rows.
    7. Prints instructions for modifying the watch_pane script to update the readout regions. The actions depend on whether you are calibrating a mirror or the grating:
      • Mirror:
        • The script prints a new value of WINDOW for you to cut and paste into the appropriate line in the watch_pane script.
        • The script prints instructions for how to acquire a new image to check the MIRROR OFFSET parameter and insert this into the watch_pane script.
      • Grating:
        • The script prints a line defining the GRATING WINDOW for mask area imaging and another defining the GRATING OFFSET parameter for AlignArea imaging.
        • Insert these lines in the appropriate place in the watch_pane source code.
  6. Install /kroot/src/kss/deimos/fiord/deiccd/watch_pane as dmosbld at vm-deimosbuild using make install. Use kdeploy -a to deploy the changes.
  7. Verify AlignArea offset.
    1. Acquire an image in AlignArea mode by running take_autopane_image -v This will insert a user mask (presumably with alignment boxes) and acquire an image in AlignArea mode.
    2. Launch the SAT if it is not running, select ID boxes and load the image.
    3. Verify that all boxes are found. This establishes that all boxes are on the image.
    4. To determine whether the proper number of leading and trailing rows was included in the image, load the image into ds9 using the command ds9_mosaic, or use the Ginga display GUI. Reset the scaling parameters as needed so that the maximum value is around the level of the box centers.
    5. Locate the bottommost alignment box and measure the number of rows from the first row to the row at which the box is at half the peak illumination. Compute the different (delta1).
    6. Locate the uppermost alignment box and measure the number of rows from the row at which the box is at half the peak illumination to the last row read out. Compute the difference (delta2).
    7. The values of delta1 and delta2 should be the same to within a couple of pixels and should be around 40-45 rows. If these are not equal, then you should adjust the GRATING OFFSET parameter accordingly until they match:
      • If delta1 > delta2, then increase grating offset.
      • If delta1 < delta2, then decrease grating offset.
    8. Script is now working properly. Commit changes to SVN.

See Also