Multi-star guiding

[DavidTrap (David)]

Originally Posted by Paul Haese

Thanks Brett, never looked there.

Yes,

It's not in a logical spot!

DT

[Moon (James)]

Originally Posted by DavidTrap

Yes,

It's not in a logical spot!

DT

It does kinda make sense - if you enable it you should probably increase the size of the tracking box at the same time - to pick up more stars.

James

[RobF (Rob)]

Originally Posted by RobC

It would be good to hear more about the PHD2 work on multi-star guiding. Does anyone know how to get hold of the beta code or have updated on how the work is progressing?

RobF,

I can download the source for you and build it.

Rob

Thanks Rob - will send a PM

[DavidTrap (David)]

Originally Posted by Moon

It does kinda make sense - if you enable it you should probably increase the size of the tracking box at the same time - to pick up more stars.

James

There are a few things in Maxim that are tucked away in those drop down option screens, like guider settling. Once you've found them it's OK, but they're not in the first place you'd think to look.

Anyway, first world problem really.

DT

[DavidTrap (David)]

Another update.

Tonight, I've been guiding at 750mm via an OAG.

Here are the guiding graphs, first is multi-star and second is normal.

Not much of a difference and most of the corrections are less than +/- 1 arc-sec.

DT

[gregbradley]

I wonder if the improvements from multi star guiding are going to be greater if the seeing is weaker.

Greg.

[ZeroID (Brent)]

Originally Posted by g__day

Short answer (from Cloudy Nights 2013- 2014, MaximDL V5.0 plug-in and I think Criag Stark's analysis) is 50% improvement in guiding when using 3-6 spread guide stars - as averaging 5-6 stars' centroid movement tends to remove very localised seeing fluctations thereby reducing the number of false positive guide commands.

Basically if your guide camera is seeing star movement that is heavily attributable to seeing conditions - you want to remove this. It happens to me a fair bit so I tend to lengthen the duration of my guide shots from 1 - 1.5 seconds up to 2.5 - 4.0 seconds and increase how much drift I must see before a guide pulse is sent. I have found over the years at my location and on my equipment this gives me excellent, long duration, long focal length guiding.

Craig Stark wrote one or two notes over the years that basically had the theme of don't chase the seeing! It hadn't occured to me that in a guide camera's very localised frame that several stars in the frame may move in an unusual manner in relation to each other. Say you had four stars in the frame in a perfect square - well if a frame shows the four stars in a different configuration I take it that one or more of the stars are effected by seeing! So statsistically these changes in geometry (the length and direction of the guide stars from each other) can be identified and used to modify the algorithm of what drift is actually occuring!

Interesting. that kind of 'error correction' is the same as Trellis Encoding for high speed faxes ( 114.4kbaud upwards ). A pattern of voltage pulses plotted on a sinusoidal AC waveform. Basis being one spot of of kilter does not invaildate the data. Never thought my old expertise would come back to haunt me ...