How can I prevent the NexStar GPS error off of true north?
October 15, 2008
The older NexStar GPS telescopes (those with version 2.2 or older hand controls and all hand controls without versions) have the North and Level method programmed in the firmware. These scopes will align to magnetic north, which is about 10-20 degrees to the right of true north for much of western North America.
Your telescope has a compass calibration routine that allows you to correct for this error or offset. To calibrate the compass, you will need to do a successful GPS alignment and properly center the alignment stars.
Once you see the Alignment Successful message, press the Menu key. Go to Utilities – Compass. Select Calibrate and press Enter. You should see a message displaying One Moment and Calibration Success.
The next time you do an alignment, the compass calibration will compensate for the variance between magnetic and true north. Your next alignment will also be much more accurate. Your calibration is good for all observing in your region. If you move the scope to a different part of the country, you will have to repeat the process.
It’s easy to get a good alignment. Here is what you need to do:
1. After setting up the scope and leveling the tripod, turn on the scope and check your finderscope alignment.
2. Then turn off the scope and return it to the tube down position needed to start the GPS Align.
3. Turn on the scope, choose GPS Align and let it find the north and level position by raising itself and moving about. The display will show GPS Align. It will eventually slow and stop pointing about 10-20 degrees to the right (east) of Polaris. It will pause for about 5 seconds, displaying the time and position. This allows a user to make changes.
4. Enter to Accept, Press Undo to Edit will appear during this interval. If no key is pressed, GPS Align continues and the scope starts to slew.
5. The scope will slew to where it thinks the first alignment star is and will end up about 10-20 degrees right of the actual position, prompting you to center in the finder and press ENTER. Just ignore the discrepancy and do as you are told, using the arrow keys at the default rate toslew left to the star.
6. Then do the same while looking into the eyepiece, pressing ALIGN. The scope will slew to the second star, again ending up to its right by the 10-20 degrees. Center as before, with both the finder and eyepiece.
When Alignment Successful is displayed, the scope will have corrected for the difference and be properly aligned for a night’s observing.