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icon, you can click on it to return to this point.
There are two secondary mirrors, each giving the same Cassegrain focal ratio, but one being undersized for infrared observations. The secondaries are centrally supported and defined. The secondary mechanism (pod) potentially allows full remote control of the position of the mirror, however it has proved to be such a source of problems that only focus movement is routinely used. The focal position of the secondary is controlled by a stepper motor that has a unit motion of 0.00005 inch, and a total range of 20,000 steps, or 1 inch.
The fork mount uses direct-friction drives, allowing very fast slewing but having the potentially dangerous feature that the telescope can be moved by hand when the motors are not engaged. The drive motors are controlled via a PC (the "mount PC") running software supplied by Comsoft. The dome position is encoded, and when properly set will follow the motion of the telescope accurately.
An autoguider program running on a PC (the "guide PC") allows movement of the TV pickoff mirror, in the "topbox", focus of the TV, as well as autoguiding. The TV field is presently about 2x1.5 arcmin. Turn on power for the guide camera. You will find the switch mounted on the mirror cell. Make sure the guide PC is booted first. If you need to reboot the guide PC, type "Ctrl-Alt-Del" simultaneously on its keyboard. The message "You can start Realtime system on the Sparc" will appear on the guide PC monitor after a few minutes.
The topbox also has an 8-position filter wheel, which is controlled by the Sun computer ("flwo48"). The maximum filter size is 4", inserts also allow 2" square and round filters to be used. Only qualified people are allowed to change filters.
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For 4shooter
observers who want the telescope coords centered on one of the CCDs, rather
than on the center of the array, you must take the following extra steps.
After zeroing a bright star on axis, enter the appropriate offsets in the
offset menu (e.g., -350 -350 for chip 3), click on "Move to Manual Off"
and thus move the telescope so that the setup star is at the center of
your favorite chip. Cancel out of that window. Now use the "set tele pos"
from the TCS window. Make sure the coordinates shown are those of your
star.
If you don't see the star, with the TV on-axis, first consider the possibility that the previous observer zeroed the telescope on Chip 3. Try reversing the above offset (350 350) and see if the star appears in the TV.
If the coordinates are way off, and you can't find any stars in the guide TV even with putting in the offset just mentioned, you may need to resort to a more fundamental method. First go out into the dome and look through one of the finders (one has a smaller field of view than the other - use this one last). If the star is visible, center it. If no star is visible, you must stow the telescope (in the Tele Tasks menu). Go out into the dome and level the telescope using the hand paddle and watching the two bubble levels mounted on the topbox. Return to the control room, go to the Tele Tasks menu, and reset Tele Pos so that the RA is the current Sidereal Time (read off TCS window or PC-TCS on the mount PC monitor) and Dec is +31:41:18. You might have to add a few seconds to the RA set value to make sure you get the time right. Restarting the PC-TCS program will have the same effect as the above. Now, turn the tracking back on (also in tele tasks - you may need to cycle it off then on). Also, turn on dome tracking again. Now go to a bright star as listed above and hope for the best.
You should be set to observe now except for focusing. (see CCD PRIMER Focusing)
To Table Of ContentsThere is an air conditioner in the dome which should be used to keep the dome as cool as possible in daylight, but it should be turned off during observations. It is controlled by a switch in the chamber; instructions on settings are posted next to it. It is thermostatically controlled to attempt to match the evening temperature.
There is also a fan that can be turned on after the dome is opened at night (to the South of the telescope). A low speed seems to be satisfactory, but there is no established dogma.
To Table Of ContentsThere are several macros in the Realtime system that allow you to take flats in all of your filters with a single command, say while you are eating dinner. Be sure to turn off the lamps when you are done.Close the mirror covers ONLY at zenith!
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To Table Of ContentsThe software has a protection against slewing too far over. The telescope will not move if you have requested an illegal move. On the mount PC monitor, the word Next will be highlighted in red. It is possible however, to go to the limit by slewing with the hand paddle.
If you have reached the physical limit of 20 degrees above the horizon, perhaps by moving there with the hand paddle, or perhaps the telescope simply tracked into the western limit, the motors will shut off automatically. The dome may also rotate incessantly. To get restarted, first and most important, find out what you did wrong and correct that. It could be that you have reset the coordinates completely wrong, and then tried to slew to what would have been a reasonable place, but which was rendered impossible to achieve by the zero-point mistake.
In the control room, disable the telescope drives. Once you know what you did wrong, go out to the telescope and determine whether a move in RA or in Dec is needed. If an RA move is needed, push on the fork (rather difficult) for a few inches of motion. If a Dec move is needed, gently push on the top ring in an upwards direction for about a foot of motion. Now clear the "Panic" mode on the mount PC screen by typing "F9 F10 F9" (perhaps several times) on its keyboard. The dome should stop moving at this point after it has homed itself. Once both the "Panic" message and the "Disabled" messages are gone, you may turn on the drive enable switch.
The telescope may now be moved with the hand paddle or under computer control (please don't repeat the previous move). You should check the dome to make sure it is homed; if not, use the home dome button in the TCS window (on flwo48), under "Tele Tasks."
If the filter wheel and/or the pickoff mirror
stop responding, you should cycle the power to the topbox. First exit TCS
(type "bye" in the rtshell window). Second, go into the chamber and turn
off the power switch,
on the South side of the mirror cell. Turn it back on after a few seconds.
Third, reboot the guide PC, type "Ctrl-Alt-Del" simultaneously on its keyboard.
The message "You can start Realtime system on the Sparc" will appear on
the guide PC monitor after a few minutes (you should hear homing motors
inside the topbox). Finally, restart TCS,
by typing "go4" for 4shooter or goccd for Andycam, and after a few more
minutes, you will be back in action. If you are unsure about any of these
steps, please call a staff member.
If the mirror covers fail to open or close completely (e.g. 1 petal sticks), please call a staff member for guidance.
If the CCDs stop or are very slow in reading out, or you see a read error message in the TCS window, or the data are obviously distorted, you should cycle the power to the CCDs. First, go into the chamber, and turn off the power switch on the North side of the mirror cell. Then go into the computer room and turn off the FIFO. Turn it back on after a few seconds. Return to the chamber, and turn the CCD switch back on. Take a bias to see if the CCDs are performing correctly. If that still fails, you should first exit TCS (see Lost filter wheel above), repeat the CCD power cycling procedure, and restart TCS as above. If you are unsure about any of these steps, please call a staff member.
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