icon, you can click on it to return to this point.When you see this
icon, you can click on it to return to this point.
The 48" telescope is an f/8 Ritchey-Chretien reflector, with a honeycomb borosilicate f/1.9 primary mirror. It can give a coma free field of 30 arcminutes. The primary mirror is supported in its cell by a system of axial and radial actuators, whose forces are determined by counterweights. The axial and radial definitions are made by three hard points, each of which have a load cells whose force readings are displayed above the electronics rack in the control room (either radial or axial can be displayed, but not both).
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 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 running software supplied by Comsoft. The dome position is encoded, and when properly set will follow the motion of the telescope.
An autoguider program running on a PC allows movement of the TV pickoff mirror, in the Top Box, focus of the TV, as well as autoguiding. The TV field is presently about 2 arcminutes. The Top Box also has an 8 position filter wheel, which is controlled by the Sun computer. The maximum filter size is 4", inserts allow 2" square and round filters also to be used. Filters are changeable only by qualified people.
To Table Of Contents
The telescope is occasionally unplugged for safety reasons, during thunderstorms or while electrical work is being done. To start up in this case:
For 4shooter observers who want the telescope coords centered on one of the CCD's, rather than on the center of the array, you must do the following extra steps. After zeroing on axis, enter the appropriate offsets in the offset menu (e.g., -350 -350 for chip 3), and thus move the telescope so that the setup star is at the center of your favorite chip. Then on the PC-TCS computer itself, go to the "Declare" Menu (use the LR arrow keys to get there), select Declare with a CR (if the menu is not displayed already), then select INIT NEXT with a CR. Answer "W" to the question. You should now be all set. Note that using the "set tele pos" on the Sun monitor after the offsetting instead of INIT NEXT on the PC-TCS will not reset the coords where you want in this case.
You should be set to observe now except for focusing. (see CCD PRIMER Focusing)
To Table Of Contents
The Track Rate and Guide Rates are automatically reset to good values when the Tcs program starts.
There is an air conditioner in the dome which should be used to keep the dome as cool as possible. It is controlled by a PC in the 48" observers room. 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. A low speed seems to be satisfactory.
To Table Of Contents
Open the mirror doors. Slew the telescope by hand to about -28 degrees South, 0 HA (tracking off). Check the positioning by eye. Turn on the lamps with the switch on the rack, make sure all lights are on.
There 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. Only close mirror covers at zenith!
To Table Of Contents
If you have reached the physical limit of 20 degrees above the horizon, the motors will shut off automatically. 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. Once you know what you did wrong, go out to the telescope and gently push on the top ring in an upwards direction until the motors re-engage. You can now slew the telescope by hand till it is in a reasonable position.
The dome occasionally gets lost. To retrieve the pointing of the dome, go to the Tele Tasks menu of the TCS and turn off the dome tracking, and then click on Home Dome. This will send the dome to its home sensor. Now turn the dome tracking back on.
To Table Of Contents