2. Operating the Telescope and Guider

2.1 Opening Check-list

Turning On the Telescope

  • Turn the key for main power.
  • Select ``drive line.'' If drive amplifiers are working, you can switch to ``drive amplifiers.''
  • Ascertain that the digit switches are set to 60.000.
  • Turn ``sidereal drives switch" to ``on".
  • Set the Right Ascension setting circle so it reads the correct LST. (Use the LST clock or call the 2.1m operator at x8630.)
  • Check that the voltage pot for the TV camera is turned all the way down (full CCW).
  • Turn on power to the TV camera using the power supply affixed to the side of the telescope (LED's on both boxes should be illuminated).
  • Turn on TV monitor and guider flip mirror power supply.
  • Reset the shutter and filter-wheel logic by pressing the white ``STD reset" button on the the filter interface power supply box attached to the CCD mount. Move the filter wheel via the computer to ensure that the LED's turn off.
  • Ascertain that the lower clam shell is open (large wheel near the telescope base).

    To Open the Dome

  • Using the hand-paddle, position the dome to due E if it is pointing elsewhere.
  • Using the ladder, carefully plug in the cord to the outlet marked ``shutter".
  • Flip the rightmost switch to the right to open the upper shutter.
    If nothing happens, reach on top of the switch, and slide the bar to the right.
  • Once the upper shutter has risen a few feet, open the lower shutter by flipping the leftmost switch to the right.
  • The lower shutter is open when the sound changes abruptly; turn the leftmost switch off.
  • Once the shutters have stopped moving, turn the switches off, and unplug and coil the cable.
  • Uncover the telescope.
  • Uncover the guider and finder telescopes.

    To Move the Telescope

    The telescope is usually moved to its new position by unclamping the telescope in one axis, maneuvering by hand until approximately correct, and then repeating the operation for the opposite axis. However, if the telescope is in an awkward position, we recommend that you instead move the telescope using the ``slew" setting on the hand-paddle rather than attempt to deal with the situation perched on a ladder. The final adjustment of the telescope position should be done with the hand-paddle in either case.

    NEVER OPEN BOTH RA AND DEC CLAMPS AT THE SAME TIME.

  • Unclamp the telescope in one axis only using either pair of switches (located on opposite sides of the telescope).
  • Grab the telescope using one of the large clamshell wheels (not the finder or guide telescopes!) and carefully maneuver the telescope to its new position.
  • After the telescope has stopped moving, reclamp the telescope (must be done with same switch).
  • Repeat the operation for the other axis.
  • Move the telescope to the final position using the hand-paddle.

    NOTE: If the telescope does get away from you, you can reclamp it by simply TURNING OFF THE KEY.

    2.2 Reading the Setting Circles

    Both the RA and Dec setting circles are equipped with verniers. With care, the practiced observer can set the telescope to 10s in RA and 5 arcmin in declination. Examples of how to read the verniers are given in Figs. 2.1 and 2.2.

       Figure 2.1.: The RA vernier is read by obtaining the hours and minutes from the ``0" mark (16:00 here) and reading the number of seconds based upon where the marks on the two scales line up from the top scale (30s in this example). Thus the telescope is pointing to an RA of 16h 00m 30s, if the circle was set to the correct LST at the start of the evening.

         Figure 2.2: The dec vernier is read by first obtaining the nearest 15 arcmin from the ``0" mark (3 deg 30 arcmin in this example) and adding the appropriate number of 5 arcmin intervals based upon where the marks line up with the upper scale: 5 arcmin here. Thus the telescope is pointing to 3 deg 35 arcmin in this example. For negative decs the left side of the scale would have been used.

    2.3 Closing Check-list

  • Turn off the TV power supply.
  • Move the telescope to its storage position (declination; 6 hrs to the west).
  • Install covers.
  • If the rain is likely then:
          Close the lower clam shell.
          Move the telescope to zenith.
  • Rotate the dome to due E.
  • Using the ladder, carefully plug in the cord to the outlet marked ``shutter".
  • Flip the leftmost switch to the left to close the lower shutter.
  • Once the lower shutter has begun closing it is safe to begin closing the upper shutter. Flip the rightmost switch to the left.
    If you can't move the switch, reach on top of the switch, and slide the bar to the left.
  • Once the sound of the lower shutter motion changes, it is completely closed; turn off the switch.
  • If the lower shutter cannot finish closing because the upper shutter has come down too far, you must raise the upper shutter until it is clear, finish closing the lower shutter, and then close the upper shutter.
  • Once the upper shutter is done closing, turn off its switch.
  • Unplug and coil the cable.
  • Turn the drive switch to ``off".
  • Turn off the key.

    2.4 Hints for Field Acquisition
    * At the start of the night it may prove useful to acquire some familiar astronomical object, center it on the detector, and then reset the RA setting circle. One can also note what the error is in declination.
    * It is essential that you use current equinox coordinates when setting the telescope: equinox 1950 coordinates will lead to errors of 1/4 of a degree! There is an IRAF routine astutil package that can be used for this purpose.
    * With the guider TV xy stage ``centered" (as judged by eye looking at the stage), the TV shows the central 20 arcminutes of the field.
    * If you need to reposition an object by a few arcminutes, one can do this with some accuracy by first aquiring a star on the guider TV and judging the size of the motion from the fact that its field of view is 20 arcmin. The directions should be marked on the TV monitor.

    2.5 Calibration of the Guider at the Beginning of the Night

  • Wait a few minutes after telescope power is turned on to let the autoguider cool. This takes approximately 20 min.
  • Step through menu, using ``adjust" to set the following values:
       EA=3.0 [Exposure adjust]
       b=1 [Gain boost] (default)
       bA=A [Star brightness adjust (Average or Faint)] (default)
       SA=3 [Scintillation adjust]
       FL=L [Focal length of telescope (Long or Short)]
       C1=15 [Calibration time x axis]
       C2=15 [Calibration time y axis]
       H1=3 [Hysterysis X axis in tenths]
       H2=3 [Hysterysis y axis in tenths]
       AA=2 [Averaging adjust (number of cycles to average)
       AL=2 [Number of cycles between alarm beeps]
  • Put the refractor mirror into ``TV" and take a dark frame.
  • When at your first field, find a star on the refractor TV, and using the XY stage, put it precisely in the center of the grease pencil ``guider box" on the monitor.
  • Make sure the power supply on the right of the bench is turned on. Using the switch above this supply, switch to ``guider". Press ``find and focus", and check that the brightness level is adequate but not saturated (e.g., 5-98). If it isn't, choose a different guide star or see the procedure below for changing the integration time. Move the star to 50 +/- 10, 50 +/- 10 in x, y by barely tweaking the xy stage. When done, press ``interrupt" until you get the ``Hello" prompt back.
  • Press ``calibrate". The calibrate procedure merely determines the orientation of the telescope drives with motion on the guider. It will take a minute or two, and then you will either get the ``Hello" prompt back or an error indication. If you get the error indication, you must go back to the menu and change the ``ca" to a higher value. The calibration must not have any error indication. If you make very large changes in dec., you should do the calibrate again after you are set on a new guide star.


    Guider check-list for each field

  • With the refractor switch on ``TV", center a star on the grease pencil ``guider box" on the monitor by using the xy stage motion. You will need to turn up the TV voltage pot until you see sky. You can use small telescope motions if needed, but they must be very small or you will lose your field position.
  • Turn the TV voltage pot all the way down (full CCW).
  • Move the refractor mirror to ``guider" and press ``find and focus". You will see three numbers: a brightness level, and an x and y value. The brightness level needs to be between 5 and 98, and the x and y values should be near 50 and 50. If the counts are too high or too low, either find another guide star or change the exposure time as follows:
       * press interrupt to go back to the ``Hello" prompt
       * press ``menu" and then use ``adjust" to alter the exposure time (EA) to some value between 0.3 sec and 10 sec
       * press menu until you are back to the ``Hello" prompt
       * darken the autoguider by flipping the refractor mirror to ``TV", take a dark frame, and then switch mirror back to ``guider"
       * Check the brightness level using ``find and focus"
  • Press ``interrupt" to return to main menu (you will have to hold this down for the length of the integration time)
  • Press ``track". You should be guiding.
  • When ready to go to a new field, press interrupt. You will have to hold it for as long as your integration time to be noticed.

    2.6 What Can Go Wrong
    * No light reaching the detector: There is a ``clam-shell" shutter which could conceivably be closed. The clam-shell is opened and closed using a wheel near the base of the telescope; check that it is indeed open.

    1. Introduction    3. Shutter & Filter Wheel