[g__day (Matthew)]

What’s your preferred Auto-guiding software once you move past 10 minute shots?

I must admit I am struggling with auto-guiding right now, yes it works – but not with the precision I’d like on long duration shots.

Having used PHD for many months now I am about to give MaximDL a try – to see if it can give me better control and diagnostics over what is going on.

I find anything up around 6 minutes at 2.3 metre focal length to be fine (even unguided) – at around 10 minutes stars have a 2-3 mm streak (mostly in RA). At 20 minutes stars have a 4-5 mm (say a 1-2 arc minute streak). The surprising thing I am finding is that guiding the way I am doing it is not significantly improving images over my unguided shots!

My mount is on a permanent pier and aligned within 30 arc seconds of the SCP. I image off a 9.25” Celestron into a Canon 400D. When I visual sighting on a star thru the Canon’s viewfinder – and place it on the central focusing dot – the star stays there for 10 ~ 20 minutes as far as my eye can tell.

I have yet to do a PE correction from my main scope – so far I have being doing PEC using the MAK. Neither have I averaged runs from PEMPro – I am still learning how to get it all to work consistently and getting my image scale correct.

So given I have no or minimal drift in DEC, my challenge is to eliminate drift in RA. Therefore my corrections have to distinguish between seeing errors and tracking errors.

Now I have use a Meade CCD to guide, and have tried first a 480mm focal length 80mm Megrez, then a 127mm MAK with focal length 1500mm. Recently I added a focal reducer to bring the MAK to a focal length of 750mm into the DSI – to give me tighter, brighter stars.

PHD is a blessing (and its free), and Craig Stark is really brilliant at answer questions on his Yahoo group. I am now at a point where I need to enhance the performance I am achieving. I have tried using PHD analyser and reading raw PHD log files to determine what is actually occurring. I presume I am partly chasing seeing and am trying to understand where the guiding error is occurring – is the software too aggressive or too passive in how it adjusts for tracking errors?

Unfortunately there are several interacting variables to tune. Including:

1. RA aggressiveness (0.1 – 2.0 sidereal) on the hand controller (default +0.5 sidereal )
2. RA Aggressiveness 0 – 100% on PHD (DEFAULT (95%)
3. RA Hysteresis 0% - 100% on PHD (default 10%)
4. Minimum motion before pulse guide is sent 0.01 – 2.00 pixels (default 0.2)
5. Frame duration 0.01 – 10 seconds (default 1.5 – 2.5 secs)

I am now going to descend into the very bowels of PHD logs to see if I can work out what is happening, and now to fix it – wish me luck – and/or give me hints!