User's Guide to the Hamilton Spectrograph

Table of Contents

Quick Reference
CCD Characteristics
Grating Tilt & Dewar Height
Filter Wheel & Shutter
Calibration Sources
Photon Integrator
Image Rotator
Iodine Cell & Slit Room Controller
Guide Camera & Filter Wheel
Data Taking System
Hamilton Motor Controller
Hamilton Focus
More Info:
Spectral Format
Navigating the Spectrum
Table of Orders
Setup Procedures
Observing Hints

Data Archive
Mt. Hamilton Homepage

Image Rotator

Image Rotator installed position

The Image Rotator is a quartz roof prism in a clock-driven cylindrical housing which can optionally be inserted in the telescope beam about 18-inches ahead of the entrance slit. The coudé field may be rotated to any orientation with respect to the spectrograph's entrance slit (aperture plate) by manually rotating the housing. Once the desired orientation is set, the rotator's clock drive slowly and continuously rotates the prism, counteracting the inherent, hour-angle dependent rotation of the coudé field.

The rotator may be used with either the 3-m or CAT, but introduces some image degradation and slight light losses, and restricts the field of view. Field rotation is not an issue for most Hamilton programs, but some, especially those calling for longslit observations, may require the Image Rotator.

Installing the rotator is relatively easy.

  1. On the auxiliary panel hold the Rotator IN toggle switch until the rotator is in position. There is a limit switch that will stop its motion when in the proper position.
  2. Tighten the screw on the rotator installation arm fully to ensure that the rotator is solidly in the proper position.
  3. Remove the top and bottom covers on the rotator.
  4. If you are using the CAT telescope, you will need to install the two turning mirrors to direct the light through the image rotator. One of these mirrors attaches to the bracket above the image rotator. The second installs on a bracket just above the rotator installation arm screw. Note: You should install these mirrors after you have taken your polar quartz flat fields, as the turning mirrors block the quartz lamp.
  5. Turn on the image rotator. There are two switches: one for the power and one for the power test indicator lamp. When the power test lamp is turned on, it will illuminate if there is power being supplied to the image rotator. Please turn off the test lamp when not needed so that it doesn't illuminate the slit of the Hamilton spectrograph during observations.
Stowing the image rotator is merely the reverse process of installing it. Please remember to stow the image rotator at the end of your observing run as it is not a frequently used item and odds are the next observer will not be using it.

Operation of the image rotator is as follows.

  1. Point telescope at object and center on slit.
  2. Rotate the outer ring to the current hour angle.
  3. Rotate the inner ring to the desired position angle. This angle depends on whether you are using the image rotator at the CAT or 3-m telescope. For the 3-m telescope there is approximately a 2.5 to 3 degree error in the alignment so, use the folowing formulae for the position angle:
    • If PA <= 183 deg, set the image rotator PA to PA - 3.
    • If PA > 183 deg, set the image rotator PA to PA - 183.
    For the CAT telescope use the following formulae for the position angle setting:
    • If PA <= 180 deg, set the image rotator PA to 180 - PA.
    • If PA > 180 deg, set the image rotator PA to 360 - PA.
  4. Set the image rotator position angle on the Guide Parameters Tab in the autoguider software.
  5. For the 3-m set the E/W sign in the autoguider software to -1. For the CAT set the E/W and N/S signs in the autoguider softwear to -1.
  6. Make sure star is centered on the slit and start guiding.
  7. Take exposure.

Image Rotator Insert Switch

Image Rotator Power Switch

CAT Rotator Mirror Mounts

CAT Rotator Mirror Positions

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Last modified: Sun Feb 13 18:02:38 PST 2011