[sculptor]

Hi,

I finally gave up on drift alignment and built an autoguider. But a few things that helped before that fateful day:

Align once and for all: get out the lathe and make fittings for a half-inch aluminium rod (nonmagnetic) that fits where the polar scope on the CG5 ought to go. (Make sure it doesn't get crunched by the hole in the declination axis). The fitting will also fit your EQ6 when you buy it!!! Put a spirit level and a precision ($250.00) compass about half a metre down the rod. Ignore the compass and level settings for the time being. Do your alignment. Dedicate a night to it. Now put the scope in some fixed position, eg meridian/equator on west of mount, so magnetic bits in standard relationship to compass. Park car well away! Now just record, really accurately, the compass bearing. Glue the spirit level on with an acrylic wedge and superglue. Now you can REPRODUCE your alignment within seconds! (remember that the actual absolute compass reading is meaningless, due compass error, magnetic variation, where you parked your car, etc). Also watch out - even the screws in the corners of your spectacles are enough to put the compass out by a degree. Really! No keys, watches, within a metre. No cars within 4 or 5 metres: Error goes with the cube of the distance. And always in same spot due south of scope, never east or west.

The plot thickens: When doing the alignment, get out the graph paper and plot the N/S drift rate and direction as a function of compass bearing, one measurement every 2 or 3 degrees of azimuth. Be accurate. You don't even have to have found the perfect alignment - just read where your graph crosses zero.

Mark your turf: If legal and safe, hammer three 25mm dia stainless (nonmagnetic!) steel tubes into the ground (eg just below ground level) exactly where the where you normally put your tripod. Scope goes back in same spot each time. Saves ages.

Photograph the drift: When measuring drift rate, use your camera and laptop. Expose for say 1 minute, and count pixels of drift. Plot pixels per minute vs compass bearing. Same deal for the spirit level. No need to wait 20 mins.

But after you've done all that, one day, an autoguider will somehow end up in your possession - now you are doing 3 hours of astronomy and 10 mins of setup instead of the other way round.

Regarding autoguiders - must do proportional control at tiny fraction of sidereal rate, talking to CG5 directly via hand controller, not the old style bang-bang on-off control via the stegosaurus-vintage "autoguider" port. Then, it is best to put the polar axis intentionally out of alignment by say 1 degree, so that the autoguider is always working in the same direction, no backlash.

Make the motor work for its cocoa: (b) carefully put the counterweights very slightly out, so that the drive motor is always working very very very slightly against the imbalance. No backlash. Absolute disaster, whether autoguiding or not, is to have the scope wanting to lurch west ahead of the worm-drive from time to time. Even perfect balance is suboptimal, because things catch and lurch, catch and lurch.

Agree with the other folks that you're already doing superbly with a CG5. I feel they're a great "visual" mount rather than a "photographic" mount, which requires more engineering if you want 10 minute exposures.

For those that can't do any of the above, there is nothing wrong with stacking lots of 1 minute exposures using RegiStax etc. The up-side is that you can throw out those images where the wind gusted, or a cloud came. The main down-side is that the read-out error (one-off noise on each exposure) is root(10) times worse than with one single 10-minute exposure. But read-out error is usually small compared with dark current, skyglow, and hot pixels, so not to worry.

Hope these tricks help a bit.