Celestron CGE800, CGE925 manual Alignment Procedures, Startup Procedure, Calibrating the CGE Mount

Alignment Procedures

In order for the CGE to accurately point to objects in the sky, it must first be aligned to two known positions (stars) in the sky. With this information, the telescope can create a model of the sky, which it uses to locate any object with known coordinates. There are many ways to align the CGE with the sky depending on what information the user is able to provide: Auto Two Star Alignment allows the user to select two stars and uses the entered time/location information to align the telescope; Auto One-Star Alignment involves the same process as Two-Star Align, however only uses one star position to align the telescope mount. Quick-Alignwill ask you to input all the same information as you would for the Auto Align procedure. However, instead of slewing to two alignment stars for centering and alignment, the telescope bypasses this step and simply models the sky based on the information given. Finally, Last Alignment restores your last saved star alignment and switch position. Last Alignment also serves as a good safeguard in case the telescope should lose power.

Startup Procedure

Before any of the described alignments are performed, the CGE needs to first index its switch position so that each axis has an equal amount of travel to move in either direction. It is a good idea to calibrate your mounts switch position after a successful alignment (see Calibrating the CGE Mount box on this page). Once the switch position has been set, the hand control will display the last entered date and time information stored in the hand control. Once the CGE is powered on:

1.Press ENTER begin the alignment process.

2.Press ENTER again to set the telescopes switch position. Press UNDO if you would like to manually move the telescope to a different switch position. This is useful if using your scope with additional equipment attached and its range of motion is limited.

3.After the telescope moves to its switch position, the hand control will display the last entered local time, date, time zone, longitude and latitude.

•Use the Up/Down keys (10) to view the current parameters.

•Press ENTER to accept the current parameters.

•Press UNDO to enter current date and time information into the hand control. The following information will be displayed:

Time - Enter the current local time for your area. You can enter either the local time (i.e. 08:00), or you can enter military time (i.e. 20:00 ).

•Select PM or AM. If military time was entered, the hand control will bypass this step.

•Choose between Standard time or Daylight Savings time. Use the Up and Down scroll buttons (10) to toggle between options.

•Select the time zone that you are observing from. Again, use the Up and Down buttons

18

Calibrating the CGE Mount

In order to improve the pointing accuracy of your CGE telescope, the internal declination axis switch needs to be properly calibrated. This improves the pointing accuracy in two ways: First it measures and records the offset error when the declination switch is found at start-up. Second, it calculates and compensates for "cone" error inherent in all German equatorial mounts. Cone error is the inaccuracy that results from the optical tube not being perpendicular to the mounts declination axis. The mount should always be calibrated the first time it is used and only needs to be re-calibrated if the mount is used with a different optical tube or the optical tube is subjected to rough handling.

Calibrating the mount is a very easy process and takes only a minute to do. To calibrate your CGE mount:

•First, you must complete an Auto Two-Star Alignment as described in this section. However, you must take special notice to select two alignment stars that are on the same side of the Meridian (i.e. both in the western half of the sky or both in the eastern half of the sky). See Figure 3-2.

•Once you have completed a successful alignment, slew to a known star that is on the other side of the Meridian from your two original alignment stars.

•Press UNDO until CGE Ready is displayed. Press the MENU button on the hand control and select Calibrate Mount from the Utilities menu.

•Scroll down to DEC Switch / Cone and press ENTER to begin the calibration. When the display asks you to center your calibration star, carefully center the star in the eyepiece making sure to use the Up and Right arrows keys to remove any of the backlash in the gears. Press ENTER to complete the calibration process.

This calibration offset will be stored and used to improve the accuracy of future alignments.