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A couple of points about autoguiding:
1. The mount has to be polar aligned very well. Autoguiding is not a substitute for a weak polar alignment.
2. The scope has to be well balanced. Again you will get poor results with a badly balanced mount. That includes balancing it at the angle you will most likely image at. Some setups have a guide scope on top and the balance shifts with the angle. You may need a counterweight in this case or balance for the usual angle
3. No cable dragging the camera.
4. You need a fairly sensitive yet clean autoguiding camera. Lodestar is popular, I had 2 and they didn't play well with CCDsoft and are more suited to PHD or Maxim. The SBIG STi is hard to beat.
Now you can look at autoguiding.
Autoguiding through a guide scope is inferior to guiding with an off axis guider or a self guiding camera from SBIG.
The guide scope should be attached to the telescope tube not the rings of the scope so if the scope shifts slightly so does the guide scope.
When you cross the meridian the commands need to be reversed - ie reverse X box checked or do a new calibration.
Pick a medium bright star not an oversaturated too bright star and not a double star. Don't pick a star with another brighter star nearby as it can confuse the software which calculates the centre of the guide star.
Callibrate the guider (at least in CCDSoft). PHD may do this automatically. It tells the software how much of a command corrects how much of an error.
Make sure the guide camera is square to the scope and mount. Not at an angle. Some software (CCDSoft) will take an off square guide camera into account when you do the calibration but other software may not.
Chose a guide exposure long enough to get a decent brightness to the guide star and not too long so errors build up too much. I have found that varies with the mounts but as a guide better quality mounts can go longer between corrections (like 6 seconds) compared to lesser quality mounts which may need corrections more frequently like 1 second if you have a bright enough guide star.
Some guide cameras enable you to subtract a dark from the light. This is important because the software will often pick a hot pixel as the guide star and you will get odd and large errors that don't change if that is the case. SBIG STi has a shutter so it can do dark subtracts which I have found is pretty important otherwise I get the above hot pixel messing up guiding especially in warmer temperatures.
Aggressiveness is another setting. Start with 5 and see how it goes. It it takes too long to correct an error back down then increase it. If you mount and polar alignment are spot on then you can back it down.
Backlash. Some mounts have backlash and you may need to put a setting on this. I have never used this as my mounts did not seem to have significant backlash.
Min/max move. .1 min 3 secs max. Errors outside that range are ignored and no correction is issued.
What is a guide error? If you see guide errors averaging under .2 you are doing great. Over .8 and you'll see eggy stars.
If you are using PEC make sure the PEC curve is not upside down. In which case its pulling instead of pushing and it makes guiding worse. Invert the curve and see if the errors go down as they should.
Greg.
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