[Shiraz (Ray)]

Originally Posted by RickS

I set my min and max move based on the image scale (min move no less than 1/4 image scale and max move at least 2x image scale) and then tweak the Aggressiveness to account for nightly variations in seeing. That's derived from the gospel of Roland Christensen (Mr. Astro-Physics) and has always worked well for me...

Cheers,
Rick.

Originally Posted by codemonkey

The basis for my thinking is simply that if the centroid is bouncing around +/- 0.2px due to seeing fluctuations, then you can't trust movements within those bounds, only once it goes outside of that can you be sure there's something other than atmospheric turbulence at play, which is why I adjust the min motion to account for seeing.

I only tweak the aggression when I see under correction (large swings of corrections in the same direction) or over correction (zig-graph, with frequent alternating corrections).

Damping the aggression to compensate for seeing may also work well, clearly it does for you, just doesn't make as much sense to me so hasn't been the way that I've tackled it.

Thanks Rick and Lee. with aggression, hysteresis, min motion, guide rate, bearing stiction, drive stiffness, load imbalance, processing latency, scintillation etc. there seems to be too many (possibly dependent) variables to come up with a single optimum approach, so it is great to know what works.

Originally Posted by rustigsmed

That is interesting, thanks for sharing Ray. Of course a guide star isn't always so bright to allow short ones but good to know short as possible is the go.

I use a fast guide scope and can almost always find a 0.5 sec guide star - oag would be different.

Originally Posted by Atmos

With my guide scope I know I can guide on 0.1s exposures so maybe I should try super short subs

would be worth trying Colin. I also did some tests with varying sub lengths, but stuffed it up. will redo and post again.

Originally Posted by astronobob

I know not of the detailed guiding you guys do but one thing I question is why, when you say Ray quote "EQ8 system in very good seeing and with phd2" I ask, would it not defeat the purpose if your testing in as said, Very Good seeing ? Why would you not do such a test when ' seeing' is mediocre or worse ?
If you get my ' Drift" :-)
Respect & Rgrds !

good point Bob. I will redo the test when the seeing is crappy. I suspect that the results may also be specific to the mount type - the EQ8 has 8 inch wheels and probably generates less mechanical noise than smaller ones, so it may possibly do better with short guide exposures - but that is entirely conjecture.

regards Ray