Autoguider Troubleshooting

First of all make sure that the autoguider camera works reliably as a basic imager, by running it in continuous mode.

Telescope Not Moving

To verify whether your telescope is being commanded to move during guiding, click the Move button on the Guide tab. Use the Manual Control to move the motors in several second bursts. You should be able to see motion of the image. If you are doing this indoors, on most telescope mounts you can hear a difference in the motor noise levels when you click a button (you may need to hold your ear up to the motor).

Make sure you have set Control Via properly (Guide tab Settings). This determines how the autoguider commands are sent to the mount. If it is set incorrectly, the commands will not reach the mount. Please refer to Guider Settings for more information.

An extremely common failure point is the cable that sends autoguider pulses to the mount. These often run from the guide camera directly to the mount controller. These cables usually use telephone-style jacks, which are not terribly rugged. If the mount does not move in all four directions, a bad cable is probably the cause.  These cables look very much like telephone cables, but they use all six pins whereas most telephone cables have only four pins. Also the cables can be assembled with the connectors in two possible orientations, and if the connectors are attached incorrectly the wires will be reversed.  If reversed this can cause various symptoms including no motion, continuous motion on one axis, and in some cases hardware damage.  Please note that some older drive controllers require an isolation relay box on the guide port; be sure to check with the manufacturer before making the connection.

Star Not Found

Always take an Expose-mode image first, before you select Tracking. This allows the software to auto-select the guide star it will use for tracking. At this time it also measures the brightness of the star, and this is used to detect guide star fades. If you wish to manually select the guide star, click on the star once, do not drag a box. Also remember to start tracking reasonably promptly after the Expose-mode image, to ensure the guide star does not drift away in the meantime.

You will be able to guide on a fainter star than will work for calibration. The calibration routine is deliberately more discriminating, to avoid it chasing after the wrong star or image artifacts.

Please note that some autoguider setups work better with 2x2 binning, while others work better with 1x1 binning. Longer focal length guide telescopes may require 2x2 binning, especially if the stars look like big faint blobs.

The guider calibration algorithm attempts to locate "real" stars, in order to avoid chasing hot pixels and other artifacts. Check the star with the Graph Panel in Star Profile mode. If the star has a big, flat top, then it is excessively saturated. If the star has a large, flat top it won't be recognized as a star, even though you can see it in the window. The solution is very simple: use a shorter exposure or a fainter star.

Some low-cost autoguider-only cameras and all webcams have 8-bit A/D converters. It is extremely easy to oversaturate stars with these cameras. Again, look for flat tops on the image.

Star recognition during tracking is deliberately more forgiving that during calibration, since the track box is usually small enough to isolate a single star.  It is quite common to be able to track on a star that you cannot calibrate on.

Calibration Does Not Produce "L" Shape

Please note that you do not have to recalibrate all the time; in fact, this is discouraged.  The guider settings are remembered, and as long as you turn on Auto Pier Flip (for German Equatorial Mounts only) and Auto Declination Compensation, then recalibration is not necessary.  In fact, if you don't change your equipment configuration between sessions, you can reuse the same calibration for months or even years. (Some mounts behave a little differently during pier flip; if you find the tracking doesn't work after a pier flip then check the Advanced Settings.)

The autoguider calibration procedure performs four moves, and traces the movement of the star for each move. This is traced on the screen with a red "L" shape, if it is working properly. The lengths of the sides of the "L" can be different, but they should be at right angles.

The star needs to move at least five pixels during each calibration step.  If it does not move at all, see Telescope Not Moving, above. If it is not moving far enough, then either increase the Cal. Time setting(s) or increase the mount's guide rate.

If you have a wide field autoguider, so there are many stars in the field, MaxIm DL will automatically use auto star matching instead of the single star detection method.  This matches all of the stars in the field, which produces a more robust result.

If your autoguider has a narrow field of view, MaxIm DL will look at a single star in the frame. If there are a small number of stars this can potentially confuse the calibration, particularly if stars are moving in and out of the frame during the motions. You may wish to find an isolated, reasonably bright star (say 6th magnitude) and center it in the chip before starting calibration.

Autoguider Oscillates

If the guide star seems to bounce back and forth rapidly, your calibration is likely wrong. Try increasing the Cal. Time setting so that the calibration moves the star a larger distance on the guide sensor. If it only moves a small distance, mechanical problems like backlash may make the measurements inaccurate.

Also try reducing the Aggressiveness setting in the Guide tab Settings dialog box. Generally speaking, correcting 100% of the error (Aggressiveness = 10) is unwise because in theory it is on the critical edge of instability. A lower setting will make the autoguider corrections more stable and prevent overcorrection. In most cases it is recommended that you use a setting no higher than 8. For mounts with very smooth tracking you may wish to back the aggressiveness down to 3; this has the advantage of smoothing the guider corrections, effectively averaging successive guider measurements.

You can try experimenting with the backlash settings; however, it may be better to use the Anti-Stiction feature rather than play with backlash settings. The backlash features works by sending an extra-long pulse out to the mount whenever the declination direction reverses. The amount of time of this extra pulse is entered in seconds. Backlash compensation is usually only required on the Declination axis since the sidereal tracking normally runs out the backlash in RA. Be careful, however, not to set the backlash time too high – that will make the situation much worse. It is far better to set it too low than too high. Also make absolutely sure that any anti-backlash feature in the telescope mount controller itself is turned off. If the mount performs its own anti-backlash functions the star will still be moving when the guider takes the next exposure, and severe instability can result.

Some mounts, such as those equipped with Losmandy Digital Controllers, do not like RA and Dec corrections occurring right after one another. You can set an extra time delay between these corrections using the Guider Settings Advanced Tab. Other ”finesse” features are available, such as minimum move and maximum move parameters. Be careful when playing with these settings since you can render the autoguider non-functional with incorrect settings!

Stiction can cause autoguider oscillation, so try using the anti-stiction feature.  Please see the section Backlash and Stiction for an explanation of stiction.

Other Things to Check