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Old 11-06-2012, 07:27 PM
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Paul Haese
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STL11000 Guide settings

Last night I setup the GSO RC12 with my STL11K and proceeded to image the Trifid. What I found disturbed me in that my normal guide settings did not work well with a focal length of 2400mm. I initially had aggression set at 4 for each X and Y. I went down as low as 3 on each but the guiding was all over the graph and in fact going above and below. I then changed the movement jumps from 2 pixels maximum to 1.3 in each and still no improvement. Finally I went back to the default settings with aggression set to 10 and this gave a marginal improvement.

All this through the internal guide chip. Is this normal? Will using a MOAG improve the situation?

I would really like to nail this problem down. Anyone got any suggestions? I am all ears.
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Old 11-06-2012, 07:47 PM
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Octane (Humayun)
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That sounds really bad, Paul.

Frank (spearo) uses his STL-11000M with internal guider on his C14 and gets perfect round stars.

I'm not sure what the issue is. Did you calibrate the guider before guiding?

I use 2.5 second guide exposures and bin 2x2 on the guider.

H
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Old 11-06-2012, 08:02 PM
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Yep calibrated fine on all occassion. It does take big steps for calibration though, but it does calibrate. Funny thing is that the stars are round. Weird? Narrow field is tougher for guiding. Perhaps Frank will give me the benefit of his wisdom?
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Old 11-06-2012, 09:30 PM
cfranks (Charles)
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Paul, My guiding last night was also all over the place so I suggest you were suffering from poor seeing as I was. My variations were going from 0.6 to 1.8 in 1 step and then 5 or more steps to get back smooth again. I have a 10" RC 1850mm fl. so not as sensitive as yours.

Charles
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Old 11-06-2012, 09:54 PM
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Thanks Charles. Hmmm
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Old 12-06-2012, 09:46 AM
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Paul.
I find this a bit with my ST10 at 1800mm fl when the seing is poor
Yuo must remember that when you are watching the guider image, it is also at the native focal length. There is much more obvious movement of the star compared to when you are guiding through a guide camera at a much shorter focal length.
Try watching the guider image with the guide cable unplugged so it thinks it is correcting but isn't for a minute or so. You will still see it wandering from side to side as if it is over correcting. This is just the exaggerate seeing effect at the long fl.
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Old 12-06-2012, 01:33 PM
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Long focal length imaging will show up deficiences in your Polar Alignment and balance more than shorter focal length. It will also be more sensitive to seeing.

At the end of the day round stars are what you are after and you got that so there is no problem.

Here is what I use:

MMOAG, STi guider, 2935mm focal length or so.

Guide exposures - I vary this depending on seeing. The worse the seeing the longer but no longer than 4-5 seconds. Also depends on the brightest guide star available. I use autodark so the guiding doesn't pick a hot pixel by mistake over the guide star.

Usually I use 2 maybe 3 second guide exposure and sometimes 1 second if a bright guide star. I find the guide star can affect guiding quite a bit so if I see bad errors my first action is to try another guide star.

Callibration with a PME is really fast. I use about 30 pixels travel and it takes about 20 seconds to do a callibration run.

Aggressiveness is usually about 7 to 10. If it is jumping around too much I set it a bit lower.

Min move .1 Max move 1. I don't want corrections over 1 as usually that is seeing or PE not actual drift.

I use PEC and this usually seems to increase the errors but it is really adding or subtracting the PE curve to the corrections needed so you may see larger errors but its actually more accurate and you get rounder stars.

I don't see you have a problem here as your stars are nice and round.

You can always get a bit better by improving the polar alignment with T-Point, checking your balance, making sure everything is tight and no flex etc etc.

MMOAG in theory would do no better than self guiding as they are both guiding through the scope. The only advantage of MMOAG is you can use a more upspec guide sensor ( the ST237 chip is pretty noisy and low res but it works) and you can guide narrowband images. Its also a bit easier to guide blue exposures which can be dull for guide stars. Otherwise self guide is great and I wish I had it on my FLI sometimes. Although I like the new SBIG filter wheel guide camera. I wonder if that filter wheel would work with a FLI camera? FLI filter wheels are very expensive (AUD$2200 including shipping and GST).

I find guide errors with my CDK17, STi and PME with PEC running at around .2 to 1.3 error size. When its running nicely with decent seeing it will be around .1 to about .6. I think I can get that a tad lower with an even better PA and more t-point model runs.

Greg.
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Old 12-06-2012, 05:36 PM
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Thanks Terry and Greg.

Terry I will try this just to satisfy my curiosity.

Greg, great info as usual. The settings you provide are a bit different to mine and I will try these at my next outting.

Lots to digest and thanks to all for the responses.
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