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Old 01-10-2014, 11:21 AM
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Camelopardalis (Dunk)
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Question Auto guiding for a dummy

Folks,

Last weekend I found myself getting satisfactory 5+ minute subs with my little Zenithstar (~340mm, f/4.7) unguided on my EQ6.

So I thought I'd give my little C8 Edge a ride, running around 1400mm or so with the 0.7x reducer. 1 minute subs were the best I could muster. I added my little makeshift autoguider kit - an old favourite but sharp and solid 60mm Tasco f/5 refractor with my QHY5L-II. This little lot was secured onto the OTA using a Celestron piggy back adapter...don't laugh too hard

I then fired up my netbook and started Metaguide, calibrated it, found a guide star and clicked GUIDE.

Needless to say, I couldn't get longer exposures without horrid star trails

So IISers, I beg you, where do I start? Obviously I'd like to get longer subs from my C8 as I have a growing list of targets that could use the focal length. However, I'm financially constrained right now, so unless I get a winning lottery ticket an OAG is out of the question. Should I just be happy and focus on wider targets with my setup until that situation changes?

Or are there settings in Metaguide that anyone could recommend I try?

I appreciate my guide scope is not mounted ideally, but the guide star stayed pretty much centred when the wind wasn't interfering and the error graph would turn into something out of a physics class. Of course I'm open to suggestions for low/no cost options there. I'm not afraid to use gaffer tape

I just feel a bit like I'm on the precipice of getting an exciting new source of data, maybe I'm not, maybe just a hard landing awaits

Any pearls of wisdom for an autoguiding dummy greatly appreciated...
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  #2  
Old 01-10-2014, 11:28 AM
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ZeroID (Brent)
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My first attempt with Metaguide went well, my second not so much but I had changed the hardware configuration quite a bit. The weather has been very uncooperative since then but I made no changes to the default settings.
I know Phd has issues when guiding near the scp, insufficient movement to detect at low f numbers. Maybe this .. ?
I'll keep experimenting when the weather gets it right. Hopefully someone else will chirp in, I quite like Metaguide and I need guiding.

Nothing wrong with gaffer tape, otherwise gaffers wouldn't use it ..
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Old 01-10-2014, 12:05 PM
glend (Glen)
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Dunk your setup seems ok to me, and should work fine provided there is no flex in the assembly. As you have seen I use Metaguide and a ZWO guidescope with an ASI130 camera to guide my 8" newt and Canon DSLR. I had star trail problems at Bretti but I was trying to do 10 minute subs. I agree with the comment concerning guiding near the zenith but believe balance has much to do with it. You want some load on the mount as it climbs RA, or drops, so that it stays 'on the gears' so to speak. My rig was neutral balanced and that might be part of my probem. My subs looked great till I enlarged them in Photoshop and saw these little trails. I plan to run more 'weight' on RA balance, DEC I am not sure about yet. My star tails only went in one direction so I assume its RA. When looking at the graph what was it doing? . I am studying the Metaguide user manual now to work out tuning.

BTW I don't image when there is a noticable wind, but my newt may have a larger sail effect. Your tails could be nothing more than wind.

Last edited by glend; 01-10-2014 at 12:17 PM.
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Old 01-10-2014, 12:28 PM
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tlgerdes (Trevor)
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How accurate was your polar alignment? How much was your guide SW trying to bump the scope? Do you have any graphs?

The secret to autoguiding is to try to not have it working. IE be that close to polar aligned that it is just helping it, not controlling it.
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Old 01-10-2014, 02:34 PM
AndrewJ
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Gday Dunk

Agree, logs will certainly help define whats going on.
Metaguide has a lot of settings to get used to, including an internal quasi stacking function that allows several hi freq frames to be averaged to come up with delta moves ( ref settings > Simulate/Integrate ).
It also allows external apps to monitor/log whats going on such that you can watch longer duration data plots to see whats going on. I am actually playing with that function now.
May pay to do a few unguided logs as well, just to see how bad/good the tracking is in the first place.

Andrew
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Old 01-10-2014, 03:27 PM
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Camelopardalis (Dunk)
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Thanks for the input, folks...

Logs...does it generate these automatically? If not, then I don't have them how, or what's best to record them?

Graphs...none of those either which graph should I be most interested in? The X-Y graph looked pretty flat.

My polar alignment was OK...Synscan claimed it was under 1 arc minute in each axis, and I did a test sub with the Zenithstar of 8 minutes and there's only a little trailing.

Apologies if it sounds like I don't know what I'm doing... I really don't
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Old 01-10-2014, 03:38 PM
glend (Glen)
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Dunk you can get that polar alignment to 0" of error on both axis on your mount if you use the Synscan V3.35 hand controller polar alignment routine under the Alignment menu. It involves doing a standard two star alignment then going to a star for polar alignment correction - where the controller will slew then ask you to adjust your target star to the centre using the Alt bolts, then it does the same again for the Azimuth. It will show you the accuracy and reperted itterations can get you to 0 0".

Its worth downloading V3.35 for that polar alignment routine, much easier to be accurate.
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Old 01-10-2014, 04:24 PM
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Camelopardalis (Dunk)
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Thanks Glen, yes I was using the polar alignment routine in Synscan 3.35, performed 3 times. Maybe it's just my mount but I can't get close to 0" especially in altitude, that only seems to move in relatively large steps
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Old 01-10-2014, 04:38 PM
AndrewJ
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Gday Dunk
Quote:
Logs...does it generate these automatically? If not, then I don't have them how, or what's best to record them?
If you open the Setup dialog, at the bottom of the first screen is a button to allow you to tell Metaguide where to store the logs and any "saved" images.
On the main Metaguide screen, just to the left of the AFWHM/Seeing graph ( bottom left ), is a checkbox called "Log", which toggles logging on and off as reqd.
When you do a run, you should check this, and then uncheck it after the run is done, and it will create an individual logfile.
Ie if you want to calibrate and run unguided then guided, you would
a) Set logging ON,
b) Do the Calibrate
c) Set logging Off
d) Set Logging ON
e) Get a lock and then log the "unguided" error plots
f) When done, Set logging Off
g) Set logging ON
h) Select "guide"
i) When done, Set logging Off

That will create three individual logs that can be compared against each other. ie you can overlay guided against unguided.
I have written a app to import / display Metaguide logs, but as per his help file, the logs are formatted such that they can be imported directly into excel etc.

Andrew
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Old 01-10-2014, 06:39 PM
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Camelopardalis (Dunk)
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Got it, thanks Andrew - will experiment (hopefully) soon
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Old 02-10-2014, 06:46 PM
Garbz (Chris)
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How long was your exposure on the guide-cam? I've seen a lot of people recently guide at 0.5s or 1s or some short duration in an area with bad seeing. The guide scope then chases the seeing and causes trailing where there would otherwise be none.

Also I notice you forgot the step where you slaughter the goat and spread the entrails around the telescope. Don't make the mistake of using a rabbit, the gods don't like that one bit.
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Old 02-10-2014, 08:03 PM
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Amaranthus (Barry)
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Dunk, I could not get rid of flexure-induced 'creep' on my C8 when using a guidescope. Evidence: http://www.iceinspace.com.au/forum/s...d.php?t=124484

So I switched to an OAG. It works a dream, now I can readily do 20+min subs with round stars. And it would suit your QHY5L-II (which is very sensitive, and has the same chip as my ASI120MM).
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Old 03-10-2014, 12:16 AM
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Quote:
Originally Posted by Garbz View Post
How long was your exposure on the guide-cam? I've seen a lot of people recently guide at 0.5s or 1s or some short duration in an area with bad seeing. The guide scope then chases the seeing and causes trailing where there would otherwise be none.

Also I notice you forgot the step where you slaughter the goat and spread the entrails around the telescope. Don't make the mistake of using a rabbit, the gods don't like that one bit.
Sadly, only sheep were available nearby, so I had to do without

I think my guidecam exposures were set to 200ms. What is a good value to try?

Quote:
Originally Posted by Amaranthus View Post
Dunk, I could not get rid of flexure-induced 'creep' on my C8 when using a guidescope. Evidence: http://www.iceinspace.com.au/forum/s...d.php?t=124484

So I switched to an OAG. It works a dream, now I can readily do 20+min subs with round stars. And it would suit your QHY5L-II (which is very sensitive, and has the same chip as my ASI120MM).
Yeah I was trying to avoid the spend as long as possible, so I may just have to stick with the wide field stuff for now

I've added one of the "guided" images I took that evening, although I'm not sure if it gives any more clues
Attached Thumbnails
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Old 03-10-2014, 04:52 AM
AndrewJ
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Gday Chris
Quote:
I've seen a lot of people recently guide at 0.5s or 1s or some short duration in an area with bad seeing. The guide scope then chases the seeing
You will note i mentioned earlier thet Metaguide has a quasi stacking function to get around this, but i am still playing with it.
Basically, Metaguide uses frames at 0.5second intervals when not guiding, but when you guide, you can select the actual guide freq and averaging you want to use. ( ref the integration mode in the help )
In this mode, lets say your camera grabs data at 15fps
You may tell it to average 10 frames and then guide at 1second.
The guiding uses the centroid of the integrated image
thus ( hopefully ) averaging out the seeing.

Andrew ( still playing with the function )
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Old 03-10-2014, 07:48 AM
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Amaranthus (Barry)
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That GC image looks very much like differential flexure to me, Dunk.
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Old 03-10-2014, 11:33 AM
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Camelopardalis (Dunk)
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OK thanks chaps.

If I'm suffering flexure I'll have to stick to wide field for a while
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Old 03-10-2014, 08:00 PM
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ZeroID (Brent)
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Quote:
Originally Posted by Camelopardalis View Post
OK thanks chaps.

If I'm suffering flexure I'll have to stick to wide field for a while
OK, time to hit the workshop and make a better mount for the guide scope. I've been down that path and you really have to beef it up to get the system aligned and stable. Bunnings and Aluminium is your friend. Post a pic of your current setup and lets see if we can lock that puppy down.
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Old 03-10-2014, 09:59 PM
Garbz (Chris)
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Quote:
Originally Posted by AndrewJ View Post
You will note i mentioned earlier thet Metaguide has a quasi stacking function to get around this, but i am still playing with it.
Yeah I missed this. Point is still relevant though. Even at 1 second you can still be chasing the seeing. I live near the coast so I rarely guide under 3 seconds these days. You need to ensure you're averaging enough frames.
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