Tracking Log Acquisition Tips

This topic outlines many important considerations when acquiring PrecisionPEC tracking data.

Locating a Suitable Star to Track Using TheSky6 Professional Edition

Use TheSky6 Professional Edition to locate an appropriate star to track and create the Imager.log file. The star you select must not saturate the detector, and must be sufficiently bright so that it can be tracked using the shortest possible exposure, for example 0.11 seconds for most SBIG cameras. Sixth magnitude stars normally suffice. The brighter stars saturate the detector and therefore cannot be used.

Choose a star that is very close to declination zero. The target declination zero is shown below. Enable the Equatorial Grid in order to see the lines marking RA and DEC. Use View | Display Explorer | Equatorial Grid and make sure it is enabled. Also make sure that the meridian line is set to visible as well. The Meridian line is shown as red on the chart below.

Several periods of the worm (approximately ten to fifteen minutes of data) need to be collected. Be sure to select a star that is on the West side of the meridian. This ensures that there is no chance of tracking past the meridian (so that the Paramount must stop tracking).

If this is not possible make sure that you start the exposure far enough away from the meridian on the East side so the mount will not track to the meridian. See image below.

Since PrecisionPEC removes the effects of seeing, you need not be overly concerned about imaging near the horizon. However, keep in mind that with very long focal lengths the seeing close or near the horizon can cause the star to fall out of the small tracking box.

Note declination 0 degrees.

CCDSoft Setup Tips

Please read the Collecting and Using Periodic Error Tracking Data topic first. This documentation is intended to supplement the information provided in this topic.

Make sure the CCD camera is oriented correctly. The camera's detector must be oriented so that North is "up" when collecting tracking data. That is, North should point toward the top of the computer screen when images are displayed. If North is not pointed up, then the maximum magnitude of the periodic error is not being recorded.
Use the Camera | Autoguide | Imager option to record the tracking data, and not the Autoguider option. There is really no good reason to use the smaller, off-axis autoguider detector. Switch to the Imager camera on the Autoguide tab.

Using the larger, on-axis detector it's quite simple to place an appropriate star in your larger field of view. The star need not be centered. Make sure you have sufficient "area" for the star to drift over 10 to 15 minutes, without tracking out of the field. The ability to track on a star depends on the accuracy of polar alignment. Remember, polar alignment error causes drift in declination. Orienting your camera with North up can help troubleshooting tracking errors.

Place the star on Imaging detector. Note that centering the star is not necessary.

Disable autoguiding relay corrections in CCDSoft. You must manually disable autoguider corrections in CCDSoft before collecting tracking data. To do so, clear the Enabled option for both X-axis and Y-axis (see the screen shot below).

Remember, corrections made while logging (using either the relays or DirectGuide, or by moving the mount in any way, make the data unusable.

Don't forget to delete the log file before each tracking log. Otherwise, the data is appended to the end of an existing log.

Having Difficulty Tracking a Star?

If the mount's polar alignment is sufficiently poor so that drift in declination causes the star to move outside of the tracking box over a 15 minute period, you may need to increase the default size of the tracking box. If possible, refine the polar alignment first.

The default size of CCDSoft's tracking box is 32x32 pixels. The smaller the tracking box the better because of optimal data transfer rates.

However, because no tracking corrections are made, the star may not remain within this region. If the star wanders outside of the tracking box, you will have to either improve the polar alignment, or increase the size of the tracking box.

Keep in mind that the larger the size of the tracking box, the longer the time to download the image from the camera, and the quality of the tracking data may be compromised. If the orientation of the camera is north "up," and know which direction the star drifts out of the box over time (depending on which side of the meridian the telescope is on) you can increase the size of the tracking box in one direction only to create a rectangular image.

The size of the tracking box you be increased by editing the Windows Registry. Keep in mind the larger the box the slower the readout!

Changing the Size of the Track Box

See the following Software Bisque Knowledge Base article 1184 for details on how to change the size of CCDSoft's tracking box. Note that you must be a member of the Software Bisque Support Corner to view this article.

What Should the PrecisionPEC Data Look Like?

Here is an example of data from the Paramount GT-1100S. The mount is about five years old, and shows an error of about 2.3 arcseconds peak to peak periodic error.

Example Paramount GT-1100S data