Main Menu - Telescope Control - Telescope Functions I
Telescope Functions I is the first list of ten telescope control functions that ITAS-18 can perform. A horizontal menu will appear that looks like the following:
The first item is a help screen, which simply translates the mnemonics of the menu into phrases that explain the functions. They are:
|F1 - Help||F6 - Start Track|
|F2 - Next Group||F7 - Stop Track|
|F3 - Filter Select||F8 - Comments|
|F4 - System Changes||F9 - CCD Camera Control|
|F5 - Focus||F10 - Home|
The hot keys for the Telescope Function menus are the function keys.
Next Group (F2) will bring up the selection set window that will allow you to select a new star. Once again, only stars that have altitudes of at least 20° will be on this list. The telescope will move to the star position and the filter wheel moves to the first position of the observing program.
Filter Select (F3) allows the user to select the filter. A window will appear with the full set of filters available. Press the first letter of the filter name and the filter wheels will rotate to that filter.
System Changes (F4) will bring up the following window.
|Telescope System Parameters
|(A) Track Rate||163.825|
|(B) Declination Factor||0.3835|
|(D) Slew Rate||20000|
|(E) Set Rate||550|
|(F) Guide Rate||10|
|(H) Backlash Correction||+GYM3550-G|
(A) The telescope tracking frequency in hertz.
(B) The ratio of the gear ratios on the two telescope axes.
(C) The motor acceleration in microsteps/sec2.
(D) The motor rate acquired with the paddle in the slew position or the top speed during automatic moves in microsteps/sec.
(E) The motor rate acquired with the paddle in the set position in mircosteps/sec.
(F) The motor rate acquired with the paddle in the guide position in mircosteps/sec.
(G) Automatic moves to the east are programmed to overdrive and then come back west to compensate for the backlash in the worm gear. This item is the string segment that accomplishes the backlash correction. The numerical value is the number of motor steps issued for the correction.
Changes are accomplished by using the cursor keys or ENTER to get to the item of interest. You must then move to the last entry and press ENTER for the change to take effect. Since all automatic moves in both axes rely on the track rate, changing the track rate will produce a compensating change in the declination factor. The declination factor, on the other hand, only affects moves in the declination axis. Changing the basic rates and acceleration is not recommended unless you have experience with the Superior cards or similar stepping motor controllers.
The backlash compensation can be adjusted by moving between two catalog stars in close proximity to each other. With the more easterly star centered, make the west move to the other. Since no backlash correction is required here, the new star should be in the center of the field. If necessary, adjust the track rate. The move to the east will incorporate the backlash compensation, which can now be adjusted for precision moves.
Focus (F5) drives a stepping motor on the secondary mount in order to focus the telescope. Make sure that there is a star in the field of view. The preferred method for acquiring the focus function is by pressing the top right button of the hand paddle. A pop-up window instructs the user to press the north or south hand paddle keys to focus and the top right button to disable the function.
Start Track (F6) and Stop Track (F7) are complimentary functions. The transmission to the telescope electronics is checked character by character for accuracy. Should you find it necessary to turn off the tracking motor, you will interrupt this process. The solution is item F7. You will note that the "Y" of the tracking message at the top left now does not change color. Item F6 is used to restore tracking. These functions will find use during flat fielding and other calibrations. If you ever find need of it, remember that the sky keeps turning, even if the telescope does not track. Once tracking is reestablished, automatic moves (such as the move to HOME) will not bring the telescope to the expected position.
Comment (F8) allows the user to insert comments into the CCD FITS header. A window will appear which will ask for the message. This item is useful for noting weather conditions that might affect the data, procedural problems, or hardware failures.
CCD camera (F9) brings up an extensive set of functions used for the control of the Photometrics, Ltd. Star 1 CCD camera and are described separately.
Home (F10) commands the telescope system to return to the HOME.