umasscrew39 cause of the elongated stars or is there something else going on?
First, try to determine where the elongation is coming from.
Try a 10 second exposure. If there is a tracking bug (not turned on), the elongation will be around 2 arc minutes. If it is a guiding error, you should see an elongation that is no more than 50 arc seconds.
If it is the former, the elongation is only in the RA direction. If it is the latter, it can be in any direction (depending on whether the RA gears or Declination gears (or both) that are at fault.
If it is a tracking bug, you'll need to figure out why tracking is not initiated. Remember that a slew will not initiate tracking, but most mounts will start tracking once you issue a GOTO command (and if you are using ASIAIR, there is a bug where tracking cannot be manually turned on, except by issuing a GOTO).
Another thing -- if the elongation is doubled (30 arc second per second of exposure, instead of 15 arc second/second for a stopped mount), the mount is tracking, but thinks you are in the southern hemisphere when you are really in the northern hemisphere and vice versa.
If you decide the elongation is caused by poor autoguiding, there are some things that you can mitigate it. Strain wave gears are harder to guide, but not impossible; you just need to know what you are fighting against. My RST-135 guides typically at better than 0.3" to 0.4" total RMS, for example.
(1) if your mount has high periodic error slopes (discussed ad nauseam on this forum), use fast guide FPS. Something like 2 FPS (usually achievable by using 0.5 second guide exposures) is needed. You must turn on multi-star guiding at these frame rates, and you must see more than 10 stars to overcome "seeing." Because of these requirements, a decent guide scope and wide guide camera FOV are mandatory to get as many stars as you can. Two or fours stars won't help mitigate "seeing" much. And, if you have a singular very bright star in the field, increase the guide camera gain so that that bright star is saturated and is ignored by the guide program -- you want all the stars that are picked for guiding to have similar brightness.
(2) in spite of the high slopes from ZWO mounts, many of them can make use slower guide rates than the typical default (0.5x sidereal rate) -- each factor of slow down will decrease guding error by the same factor. Use guide rates that are slower than 0.5x sidereal, unless the guide pulses show that you really cannot keep up (i.e., lots of guide pulses and still not keeping up). If 0.25x sidereal rate does not work, try 0.3 or 0.4x sidereal rate guiding. Every little bit helps, and helps a lot.
(3) limit the max pulse duration to be no larger than neccessary, otherwise the guider will create havoc (large swings back and forth) whenever there is something (like a wind gust) that is not caused by the mount's own periodic error. With 0.5x sidereal guide rate, most ZWO mounts won't need a max pulse duration that is longer than 80 milliseconds (yes, 80, not a typo; not the 2000ms that ZWO recommends). Double that number if you use 0.25x sideral rate. You can determine how low you can make that max pulse duration number by guesstimating the slope of your periodic error.
(4) do not be tempted to try to use high amounts of feedback, even though it might help momentarily. Keep the aggressiveness under 40%. Go as low as you can to keep up.
With all the current software, all of these will make dither recovery slower, so you might want to keep dither small and use fewer of them if that is a problem. (This is solved by writing your own software and not limit the max pulse duration during dither recovery.)
Chen
