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What does good guiding look like?
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Roland Christen
Hi All,
Below I have posted two screen shots of guiding with the 110GTX scope piggybacked on a 12" astrograph on my 1600 AE mount. I don't use separate guide scopes because the ones available have too short of a focal length and cannot really produce accurate guiding of the caliber I want when testing scope optics. I use off-axis guiding so that there is never a question of differential flex. Using the imaging scope focal length allows much more precise guiding than a small wide field finderscope. I use MaximDL because the settings are simple and I'm very used to it. It may indeed be that PHD2 is a better guide program, and I have used it as such. But generally Maxim DL fits my needs.
Here in Hawaii we sometimes get very good seeing conditions when the winds are coming off the ocean, which was the case for these guide results. The first screen shot shows guiding at around 0.13 - 0.14 arc sec rms. This means that the seeing was quite steady and the guide star was not jumping around much. There were plenty of times when no guide corrections were needed. My settings for Min Move was 0.3 arc sec, exposure was 2 seconds and time between exposure was 5 seconds.
The second run I had some small passing clouds that disrupted the guide star position and brightness during a 300 second exposure of the main camera. Even with this disruption, the main image star size was not impacted and is actually smaller than the first image.
Except for the disruption by passing clouds, you can see the level of guiding that can be expected with the 1100/1600 AE encoder mounts. But you need good seeing to get these kind of results. If the seeing is poor, there is no way to get good guiding of this level. You need to judge the seeing by doing a short unguided run to see what star motions you get on your guider graph. Then set the Min-Move accordingly.
Roland Christen
Astro-Physics Inc.
  -- Roland Christen Astro-Physics |
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Brian Kaine
Roland,
I first began guided imaging in 2007, using an AP900 and an OAG running under MaxImDL. My primary mount is now a Mach2, but my guiding software is still MaxImDL. As you say, the settings are simple, and they work for me. I have never used anything else. When things work, I don't like to change them. To paraphrase Charlton Heston, they will have to pry MaxImDL (and AP mounts) from my cold, dead hands! Brian |
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Cheng-Yang Tan
Here's my contribution with my AP1100AE in my Bortle 7 skies when guided in my subdivision when the seeing is as good as it gets:  Here's when I was imaging through clouds  Note that for the first 6 min with guiding off (yellow box), you can see that the seeing is not that great. But with guiding on, I can still get < 1 arcsec rms error. So, IMO the AP1100AE is really impressive. cytan
On Wednesday, March 22, 2023 at 05:44:26 PM CDT, Roland Christen via groups.io <chris1011@...> wrote:
Hi All,
Below I have posted two screen shots of guiding with the 110GTX scope piggybacked on a 12" astrograph on my 1600 AE mount. I don't use separate guide scopes because the ones available have too short of a focal length and cannot really produce accurate guiding of the caliber I want when testing scope optics. I use off-axis guiding so that there is never a question of differential flex. Using the imaging scope focal length allows much more precise guiding than a small wide field finderscope. I use MaximDL because the settings are simple and I'm very used to it. It may indeed be that PHD2 is a better guide program, and I have used it as such. But generally Maxim DL fits my needs.
Here in Hawaii we sometimes get very good seeing conditions when the winds are coming off the ocean, which was the case for these guide results. The first screen shot shows guiding at around 0.13 - 0.14 arc sec rms. This means that the seeing was quite steady and the guide star was not jumping around much. There were plenty of times when no guide corrections were needed. My settings for Min Move was 0.3 arc sec, exposure was 2 seconds and time between exposure was 5 seconds.
The second run I had some small passing clouds that disrupted the guide star position and brightness during a 300 second exposure of the main camera. Even with this disruption, the main image star size was not impacted and is actually smaller than the first image.
Except for the disruption by passing clouds, you can see the level of guiding that can be expected with the 1100/1600 AE encoder mounts. But you need good seeing to get these kind of results. If the seeing is poor, there is no way to get good guiding of this level. You need to judge the seeing by doing a short unguided run to see what star motions you get on your guider graph. Then set the Min-Move accordingly.
Roland Christen
Astro-Physics Inc.
-- Roland Christen Astro-Physics |
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For me, good guiding looks like an RMS guide error of 0.5 arcsec or less. The attached screen shot of Maxim's autoguider error graph from four years ago shows an exceptionally good run, but typically I see errors of 0.4" to 0.6".
I have a 1200 mount with a 130mm f/7 APO on it. Guiding is accomplished with a 60mm f/5 refractor and an ASI-120 camera mounted on its own dovetail plate alongside the main OTA. Photo here: <http://astronomy.mdodd.com/observatory.html#Imaging> I use MaxIm to guide with ASCOM DirectGuide (Pulse Guide? Which is the correct name?). There is no differential flexure between the main OTA and the guider. The guide camera is _not_ attached to the guide scope focuser; in fact, I removed the focuser pinion shaft and knob entirely. Instead, the camera is bolted to a 1/2"-thick aluminum bracket that's solidly clamped to the dovetail plate. See <http://astronomy.mdodd.com/observatory.html#Autoguiding_asi120> The green box below the photo explains how I focus the guider (rarely needed). This photo also shows how the guide scope is held securely to its dovetail mounting bracket with a metal strap (a modified hose clamp screwed to the bracket). And THAT is how I achieved good guiding. I spent considerable time tracking down and eliminating differential flexure, and the results are evident. If you're interested in my flexure saga, you can read about it here: <http://astronomy.mdodd.com/flexure.html> --- Mike |
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Cheng-Yang Tan
Oops the image with the yellow box with guiding off didn't stick. Here it is: 
On Wednesday, March 22, 2023 at 07:43:58 PM CDT, Cheng-Yang Tan <cytan299@...> wrote:
Here's my contribution with my AP1100AE in my Bortle 7 skies when guided in my subdivision when the seeing is as good as it gets:  Here's when I was imaging through clouds  Note that for the first 6 min with guiding off (yellow box), you can see that the seeing is not that great. But with guiding on, I can still get < 1 arcsec rms error. So, IMO the AP1100AE is really impressive. cytan
On Wednesday, March 22, 2023 at 05:44:26 PM CDT, Roland Christen via groups.io <chris1011@...> wrote:
Hi All,
Below I have posted two screen shots of guiding with the 110GTX scope piggybacked on a 12" astrograph on my 1600 AE mount. I don't use separate guide scopes because the ones available have too short of a focal length and cannot really produce accurate guiding of the caliber I want when testing scope optics. I use off-axis guiding so that there is never a question of differential flex. Using the imaging scope focal length allows much more precise guiding than a small wide field finderscope. I use MaximDL because the settings are simple and I'm very used to it. It may indeed be that PHD2 is a better guide program, and I have used it as such. But generally Maxim DL fits my needs.
Here in Hawaii we sometimes get very good seeing conditions when the winds are coming off the ocean, which was the case for these guide results. The first screen shot shows guiding at around 0.13 - 0.14 arc sec rms. This means that the seeing was quite steady and the guide star was not jumping around much. There were plenty of times when no guide corrections were needed. My settings for Min Move was 0.3 arc sec, exposure was 2 seconds and time between exposure was 5 seconds.
The second run I had some small passing clouds that disrupted the guide star position and brightness during a 300 second exposure of the main camera. Even with this disruption, the main image star size was not impacted and is actually smaller than the first image.
Except for the disruption by passing clouds, you can see the level of guiding that can be expected with the 1100/1600 AE encoder mounts. But you need good seeing to get these kind of results. If the seeing is poor, there is no way to get good guiding of this level. You need to judge the seeing by doing a short unguided run to see what star motions you get on your guider graph. Then set the Min-Move accordingly.
Roland Christen
Astro-Physics Inc.
-- Roland Christen Astro-Physics |
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Thanks for posting and giving us your settings Roland.
Were you using single star or multi-star guiding for any of these ? You suggested doing that in a previous post a few months back, and I feel like I have seen better results since I started doing multi star guiding. Here is a pretty typical guide graph for my 1100 Non-AE mount. This was also about an average seeing night with FWHM at focus of about 2.5. I should be getting the encoder upgrade kit soon, and I will see what I can get. Mike 
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Roland Christen
I used single star tracking. When I used multi-star I got interference from passing satellites that threw off the guider in Maxim.
Rolando -----Original Message-----
From: M Hambrick <mhambrick563@...> To: main@ap-gto.groups.io Sent: Wed, Mar 22, 2023 4:27 pm Subject: Re: [ap-gto] What does good guiding look like? Thanks for posting and giving us your settings Roland.
Were you using single star or multi-star guiding for any of these ? You suggested doing that in a previous post a few months back, and I feel like I have seen better results since I started doing multi star guiding. Here is a pretty typical guide graph for my 1100 Non-AE mount. This was also about an average seeing night with FWHM at focus of about 2.5. I should be getting the encoder upgrade kit soon, and I will see what I can get. Mike 
-- Roland Christen Astro-Physics |
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Interesting.
What is your understanding of how multi-star guiding works ? Does it use every star in the guide chip image (or sub-frame), or does it just use stars in the frame that meet certain criteria ? Mike |
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I dont know how maxim does it but my understanding of multi star guiding in phd is that it uses a selection of viable stars to mitigate error from seeing fluctuations of the primary guide star. It works exceptionally well and in my experience there has never been a scenario where MSG produced worse results than single star. This is phd mind you, not maxim.
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From my cursory inspection of PHD2 the multi star guiding looks like a fairly simple CG (Center 0f Gravity) tracker. It basically "weighs" selected targets up to, I believe 12. The selection process/criteria is where the rubber meets the road and I have not seen specifics of those algorithms. A CG tracker can reduce tracking errors very quickly with enough S/N. I always use MSG in PHD2 and always get better tracking/guiding results than point source guiding. It's the nature of the beast.
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>>>my understanding of multi star guiding in phd is that it uses a selection of viable stars to mitigate error from seeing fluctuations of the primary guide star. yes that's pretty much how it works. It's more like a guidestar + support stars than a true multiple guidestars PHD2can select up to 12 secondary stars (in early testing we ended up with star lists > 60 stars which just bogged things down without added value). It evaluates star selection over time, so it doesn't select them instantly. They get added slowly as guiding starts, and come and go based on star assessment (I'm not privy to the algorithms here). On Thu, Mar 23, 2023 at 4:36 AM Chris White <chris.white@...> wrote: I dont know how maxim does it but my understanding of multi star guiding in phd is that it uses a selection of viable stars to mitigate error from seeing fluctuations of the primary guide star. It works exceptionally well and in my experience there has never been a scenario where MSG produced worse results than single star. This is phd mind you, not maxim. --
Brian Brian Valente astro portfolio https://www.brianvalentephotography.com/astrophotography/ portfolio brianvalentephotography.com |
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Great post Mike! I see folks attach guiders with tiny dinky things with one knurled lock screw and then try and convince something to guide perfectly and be concerned abut guiding software as the issue. In my experience the key is rational min/max moves relative to guide rate and imager resolution. No matter what seeing rules all beyond a certain point. I use Maxim which guides well and use min move of 0.04s and max move of 0.5sec with a Mach 1 guiding at 1x. I almost always guide the OAG and largest excursions are well below 1 arc-sec. My with a 8" F/4.8 or a 6" F/3.85 guiding is simply not an issue at all in a sheltered dome. Recently in the interest of trading off tightness against fast cadence I decided to forgo guiding at all because my rgbl subs would be between 60 and 120s with cmos these days. Not surprisingly the Mach1 with a 6" Newt at 578mm does OK unguided. The link is to a 14.3 hour result (so so image really). 4.3 hours of data was guided and 10 hours was unguided. I will guide of course but it is nice to know it is not strictly required. I had a small 86 point APMM model in place mainly for great pointing but it did seem to help tracking too.. My PE with PEC on is almost nothing...Really cannot measure at 578mm. ~5 or 6 arc-s p-p with PEC off. FYI I clean and grease the mount every 18 months when a bad weather stretch is upon us. The AP grease kit is really nice. Mounts lives in a tiny dome and sees lots of use as I run it if I am home or not.
https://www.astrobin.com/full/eefxqw/0/ I only mention this because in my experience sorting out guiding issues my first step is to turn all guiding off and see what is going on. Then when guiding comes back online it is pretty obvious if some parameter is chasing seeing or flexure is ruining the party. A few minutes unguided solves scads of time starring at RMS errors. I had a very annoying flexure issue from the main OTA focuser in a 120mm Esprit when I added a rotator while guiding with a 60mm F/4. Te weight was too much.. Went back to OAG and all was well because the droop was a very slow running train. What I would really like is a guiding mechanism which can sample quick subs to quickly pull dither back and once there switch into a much more sedate correction. Yes multi-star works great in Maxim,, It was there before in PhD2.. I do not like it because the startup is slower than letting ACP run the guider show. Cheers all, Ron |
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ROBERT WYNNE
Dumb question here; but why can't a GPS satellite which has multiple cameras focused on PA stars be used to guide earth bound scopes - aside from the heavy communication traffic imposed on the satellite and slight time delay? -Best, Robert
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