Telescope Control
Controlling an telescope from a computer. Using Cartes du Ciel as the planetarium program and MaxPoint to clean up the telescope pointing. Cartes du Ciel talks to the telescope through MaxPoint with some ASCOM glue software in the background.
The telescope is a 14" LX200GPS(SMT) with an Autostar II controller running firmware 4.2g . Here's a list of the things I have set in the controller menu.
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In Cartes du Ciel, in the telescope options, choose "ASCOM". When connecting to the telescope, select "MaxPoint.Telescope". The software will ask you to have a look at the settings and the ASCOM telescope driver manual. Refresh rate is 2000 mS. This is fast enough to update the telescope location on the computer screen. I found that 1000 mS was too fast and caused problems with the camera software.
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Select the LX200GPS/R driver from the list. This will control the original LX200GPS telescopes with SCT optics and the later ones with the ACF optics. There are separate drivers for the LX200 'Classic' and the RCX scopes.
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Before connecting to the telescope, we can edit the telescope settings in MaxPoint. Press the "Scope Setup" button to edit a few things and select the telescope. Atmospheric pressure and temperature are required to calculate refraction.
Altitude limit is set to 90 degrees here and declination limit is 70 degrees so I don't drive a camera into the mount as the tube starts climibing north. The altitude limit can be set a little lower if the dome slit doesn't go far enough back to let the telescope point straight up. On this page, you can also edit the Horizon to help see which stars can be used to measure/calibrate the telescope pointing model. |
Here's the map of the star locations used for the current pointing model.
The round circle near the top is at 70 degrees Declination. There will be no stars inside that circle. I've asked the telescope not to point there because it will drive the camera into the mount as the tube points further north. The wavy curve is my local horizon. There will be no stars outside this curve. |
The first step is to do drift alginment. I used a Meade DSI camera and OpenPHD guiding to do the alignment. It took about 30 minutes. The drift alignment tool makes things easy.
After that, use MaxPoint to sight about 30 stars. I used the hand controller to move the star to the centre of the camera field. You could also use PinPoint LE, which comes with MaxPoint, to calculate the centre of the camera frame. We can see the polar alignment is pretty close, and the biggest source of error is Collimation - the optical axis is not perpendicular to the declination axis. In the end, the pointing accuracy is under 1 minute of arc. Everything shows up in the field of the camera. |