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Guiding Tips for the Star Adventurer GTi

Sky-Watcher Star Adventurer GTi Sky-Watcher Star Adventurer Open PHD Guiding Project PHD2 Star Tracker Guiding
Michael RingMau_Bard
•24 replies•3.3k views
Michael Ring avatar
Michael Ring avatar
The Star Adventurer is a very nice little mount that in my experience needs some tweaking in order to get good guiding.

I have spent quite a while trying to get the best possible results from that little mount, but at least for me this is still a fight somethimes.
So I thought I share my experiences and perhaps others can chime in and add their findings and experiences....

First of all, what do I consider good guiding?

For me, the main benefit of this mount is that it is small and lightweight, it is fast to set up and for that reason I use it for my Ascar ACL200 (200 F4) lens for widefield work.

I also sometimes use it for my Skywatcher 130PDS (650mm F5) which surprisingly works better than the Askar, but I would not define this as a normal usecase for this mount as the weight and the focal length are a quite a bit out of the specification of the mount.

So for the main Usecase I thing a guiding of 2" is acceptable, 1" is excellent and desireable but overall a bit of overkill.

So, here's a pic of my guiding with PHD2, this also shows most of the relevant parameters:

This 2nd picture shows the main issue I am fighting with but more on that later...




The main parameter I work with is DEC Aggressiveness.

My problem with the mount is that DEC does not stay around the zero axis, but instead it runs parallel to axis for a while with an offset of usually 2".
When I increase DEC Aggressiveness the the problem goes away but there is only a very small margin between good results and oscillation which totally kills the guiding.

I guess I found the reason for this behaviour, the DEC axis has active feedback in the form of a small encoder. When you open the case and turn the DEC axis then you can see that the encoder has horrible backlash, and my guess is that this backlash is the cause for the oscillations.

One thing that also helps is to balance the scope a little backheavy.

So how are your experiences, how is your guiding?

Michael
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Miguel A. avatar
Miguel A. avatar
Hello @Michael Ring - Thank you for this information. After trial and error, I have recently adopted a great understanding of guiding my scope. I think I am dialled in. PXL_20230204_042606066.jpg. I am new to AP (less than 6 months) and from what I know, I have not experienced issues with DEC or RA. The weight of my rig (7.02 lbs) is less than the 11 lbs max weight payload. I do agree and have my scope balanced to the rear. Please see the attached for guiding with AA+
Gustav Lundby avatar
Gustav Lundby avatar
I gave up my SA GTI. It had to large periodic error and the guiding struggled to keep it within 4". Picture shows the unguided periodic error during 10 minutes exposure where polar alignment is off 6 degree at purpose. Central star is Enif Scope is 260mm and sensor is Sony A5000 APS-C.

Michael Ring avatar
Michael Ring avatar
You could always sell pictures like this one as art smile
What guiding times did you try? Going fast (0.5s) helps me a lot….
Michael
Jeremy Likness avatar
Jeremy Likness avatar
Thanks for the tips. I consistently get just above 1" but was hoping for better. This session was maxed out weight and NO polar alignment (couldn't see Polaris and didn't have time with a short break in the clouds). It seemed to do fine. Settings are defaults it prompted me to use with my EQMOD setup.

Guiding Begins at 2023-02-12 00:24:33
Equipment Profile = Svbony Gti EQMOD
Dither = both axes, Dither scale = 1.000, Image noise reduction = none, Guide-frame time lapse = 0, Server enabled
Pixel scale = 4.07 arc-sec/px, Binning = 1, Focal length = 190 mm
Search region = 15 px, Star mass tolerance = 50.0%, Multi-star mode, list size = 12
 Camera = ZWO ASI120MM-S, gain = 48, full size = 1280 x 960, have dark, dark dur = 1000, no defect map, pixel size = 3.8 um
Exposure = 1000 ms
Mount = EQMOD HEQ5/6 (ASCOM), connected, guiding enabled, xAngle = 20.9, xRate = 3.403, yAngle = -72.4, yRate = 3.995, parity = +/-
Norm rates RA = 14.4"/s @ dec 0, Dec = 16.3"/s; ortho.err. = 3.3 deg
X guide algorithm = Hysteresis, Hysteresis = 0.100, Aggression = 0.700, Minimum move = 0.190
Y guide algorithm = Resist Switch, Minimum move = 0.190 Aggression = 100% FastSwitch = enabled
Backlash comp = disabled, pulse = 20 ms
Max RA duration = 2500, Max DEC duration = 2500, DEC guide mode = Auto
RA Guide Speed = 13.5 a-s/s, Dec Guide Speed = 13.5 a-s/s, Cal Dec = 23.9, Last Cal Issue = None, Timestamp = 2/11/2023 9:59:13 PM
RA = 11.15 hr, Dec = 15.9 deg, Hour angle = -1.40 hr, Pier side = West, Rotator pos = N/A, Alt = 53.7 deg, Az = 144.5 deg
Lock position = 642.073, 466.685, Star position = 642.073, 466.685, HFD = 3.39 px

Mau_Bard avatar
Mau_Bard avatar
Hi @Michael Ring , and first of all THANKS for your post!
It is really well done and you saved my last observation night, and gave me some understanding of what is going on with the SA-GTI.

I have a SA-GTI driving a Samyang 135 + TS2600 camera (similar to ASI2600MC), guided by PHD2. I drive it with EQMOD defining the mount as HEQ5, and it seems to work. The EQMOD site does not include the AS-GTI in the supported mounts (*).

After a couple of initial successful initial guiding sessions (layman luck?) with RMS between 1 and 2, and occasionally below 1, I started to notice large guiding oscillations bursts in PHD2, even when the mount was accurately polar aligned.
In order to solve the issue, I intuitively tried to play with the aggressiveness parameter, but I was not bold enough to reduce it to 44 as you correctly suggest here. Backlash compensation on/off was not changing things.
I tried mono-directional guiding as well and this solved the problem, but this was not a sustainable solution.

I was landing on the conclusion I made a wrong purchase, when I came across your post. I dialed then aggressiveness down to 44, as you suggest, and activated the backlash compensation to 100 as initial value, with a range up to 3000 or so. I have not yet reviewed last night PHD2 logs, but at first sight it seemed that RMS was down in the range of 1 to 2, and the guide trace is much cleaner.

All in all I am a bit disappointed by the behavior of the mount. While, on one side, it allows to build a full fledged portable telescope, on the other side I did not expect such uncontrolled oscillations, and large dec backlash, that probably is causing the oscillations, as you point out.

A clear night is expected tonight, I will do further testing, and in case I'll come back here with updates.

Thanks again Michael for opening this discussion thread!

Mau

(*) regarding using EQMOD settings with SA-GTI suggestions are welcome
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Michael Ring avatar
Michael Ring avatar
Glad my findings helped (Well, let's see how the next night goes for you…)

As a sidenode, you can also use Green Swamp Server instead of EQMOD, GSS has full support for the GTI and a more modern interface….

Also, using the new Callibration Assistant in phd2 helps, for my current usecase (135mm Samyang, ZWO ASI071pro) the mount is now plug&play, I set it up as my first mount and start shooting long before my bigger mounts are ready for the first sub….
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Mau_Bard avatar
Mau_Bard avatar
Michael Ring:
Glad my findings helped (Well, let's see how the next night goes for you...)

As a sidenode, you can also use Green Swamp Server instead of EQMOD, GSS has full support for the GTI and a more modern interface....

Also, using the new Callibration Assistant in phd2 helps, for my current usecase (135mm Samyang, ZWO ASI071pro) the mount is now plug&play, I set it up as my first mount and start shooting long before my bigger mounts are ready for the first sub....



Tx for the GSS hint. I heard about it and I never tested it just out of laziness. I will give it a try!

Let's keep in touch!

Mau
Michael Ring avatar
Michael Ring avatar
You should think about joining the Astrobin Community Survey Group, your equipment is perfect for donating a few panels....

https://www.astrobin.com/groups/5818/astrobin-community-survey/
Mau_Bard avatar
Mau_Bard avatar
Michael Ring:
You should think about joining the Astrobin Community Survey Group, your equipment is perfect for donating a few panels....

https://www.astrobin.com/groups/5818/astrobin-community-survey/

Thank you Michael for the kind invite! I have been following your group since the beginning. I am under a B7 sky, I suspect my quality is too low for a survey. Maybe (I do not promise) I make an attempt in a sky area and submit to your team for evaluation.

Mau
Michael Ring avatar
Michael Ring avatar
Ouch, Bortle-7 is hard… But try it anyway, everything helps!
Mau_Bard avatar
Mau_Bard avatar
Hi @Michael Ring , and first of all THANKS for your post!
It is really well done and you saved my last observation night, and gave me some understanding of what is going on with the SA-GTI.

I have a SA-GTI driving a Samyang 135 + TS2600 camera (similar to ASI2600MC), guided by PHD2. I drive it with EQMOD defining the mount as HEQ5, and it seems to work. The EQMOD site does not include the AS-GTI in the supported mounts (*).

After a couple of initial successful initial guiding sessions (layman luck?) with RMS between 1 and 2, and occasionally below 1, I started to notice large guiding oscillations bursts in PHD2, even when the mount was accurately polar aligned.
In order to solve the issue, I intuitively tried to play with the aggressiveness parameter, but I was not bold enough to reduce it to 44 as you correctly suggest here. Backlash compensation on/off was not changing things.
I tried mono-directional guiding as well and this solved the problem, but this was not a sustainable solution.

I was landing on the conclusion I made a wrong purchase, when I came across your post. I dialed then aggressiveness down to 44, as you suggest, and activated the backlash compensation to 100 as initial value, with a range up to 3000 or so. I have not yet reviewed last night PHD2 logs, but at first sight it seemed that RMS was down in the range of 1 to 2, and the guide trace is much cleaner.

All in all I am a bit disappointed by the behavior of the mount. While, on one side, it allows to build a full fledged portable telescope, on the other side I did not expect such uncontrolled oscillations, and large dec backlash, that probably is causing the oscillations, as you point out.

A clear night is expected tonight, I will do further testing, and in case I'll come back here with updates.

Thanks again Michael for opening this discussion thread!

Mau

(*) regarding using EQMOD settings with SA-GTI suggestions are welcome

I owe an update to the friends here and specially to @Michael Ring .

Last night I further tested the settings proposed by Michael, and this time I got an RMS most of time below 1 (!!!) - I was honestly surprised. For the record, air was extremely steady.

To summarize: In PHD2, starting from default parameters, I further lowered Dec Aggressiveness to 40, I set Dec backlash to "active" with a range 20-3000 (it stabilized in my case on values around 60), and activated the RA Predictive PEC algorithm at default parameters, exactly as suggested by Michael above.

I do thank again Michael, whose post here was instrumental to solve the SA-GTI Dec oscillation guiding issue, that in my case made the mount nearly unusable.
You saved my mount!

Good luck!

Mau
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maxchess avatar
maxchess avatar
With a lens as fast as the 135 on an SA-GTI do you need to guide? When I ran my ASI294/Samyang135 from my HEQ5pro I did 30 sec subs & didn't guide. See thisNamerica neb.  I hope that I won't need to on SA-GTI which I just bought as a travel mount and will use with an ASIair+.  The less kit to carry the better. We'll see.
Michael Ring avatar
Michael Ring avatar
I do 2min exposures with the Sigma 135, for them  I definitely need guiding, tried without and did not like what I saw, my pixelsize is 3.76um
When you use the ASI294 at binning 2 then perhaps you can get away without guiding, but guiding also helps iron out issues with drift caused by not so good polar alignment.

When you plan use ASIair+ anyway then the extra weight of the 120mm ZWO guide scope will not make much difference.
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Zak Jones avatar
Zak Jones avatar
I've successfully done 10 minute exposures on my Star Adventurer GTi without any issues, although I normally shoot 5 minutes for narrowband and either 2-3 minutes for broadband targets.

I did have to change a few settings in my ZWO ASIAIR Pro guiding menu so I can get good guiding results. From memory, I changed the RA aggressiveness to around either 70-60% and left the Dec aggressiveneess at it's default of 100%. If required, I chnage the RA aggressiveness occasionally if it's windy or I'm not getting desirable guiding results. The total RMS varies from night to night but I have sometimes gotten it down to around 0.5 RMS.

Zak smile
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maxchess avatar
maxchess avatar
Zak,
very helpful. How have you mounted your SAGti/Asiair/guidescope/S135 combo?
I used rings on a bar wen it was on an HEQ5 but wonder what the best way is on the SAGti.

Also I don’t see the merit in going beyond 30sec exposures with a very fast lens.  I think total integration time is key but longer exposures put more stress on good guiding/tracking and polar alignment. f2.8, 30 secs = f7 , 3 min aprox 

The SharpCap forums have good discussions on this but shorter does gives you more shot noise but you benefit from noise reduction from extra number of frames stacked as well as above benefits.



Max
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Michael Ring avatar
Michael Ring avatar
Gustav Lundby avatar
Gustav Lundby avatar
Michael Ring:
You could always sell pictures like this one as art
What guiding times did you try? Going fast (0.5s) helps me a lot....
Michael

This test was unguided to see the amount of periodic error! Guiding I got reasonable results with reasonable focal range and pixel size, but almost never below 4" total RMS.
I got full refund from dealer and bought an IOptron SkyHunter as replacement, Giving this the same test, the result was about 4 times better periodic error. However this SkyHunter mount still does not guide well. I believe it has to much backlash between motor and reduction gear.
Zak Jones avatar
Zak Jones avatar
Zak,
very helpful. How have you mounted your SAGti/Asiair/guidescope/S135 combo?
I used rings on a bar wen it was on an HEQ5 but wonder what the best way is on the SAGti.

Also I don’t see the merit in going beyond 30sec exposures with a very fast lens.  I think total integration time is key but longer exposures put more stress on good guiding/tracking and polar alignment. f2.8, 30 secs = f7 , 3 min aprox 

The SharpCap forums have good discussions on this but shorter does gives you more shot noise but you benefit from noise reduction from extra number of frames stacked as well as above benefits.



Max

I don't have a way of mounting my Samyang 135mm just yet, but I am definitely going to be getting the Astrodymium ring system, most likely the bundle with the ZWO EAF and flat mounting plate for my ZWO ASIAIR Pro. After that, I might put a longer dovetail on so I can achieve balance once everything is setup.

Good point, although depending on the target and filter used, I might use a longer exposure to really bring out the fainter details. Yes indeed, I think that total integration time is one of the most important things that an astrophotographer can do to help reduce the background noise and improve the signal to noise ratio.

I'll have to have a look on the Sharpcap forums when I can to find out further information. Once I get my Astrodymium ring system up and running, I will be sure to post an update on how I managed to set it up for my Star Adventurer GTi.

Zak
TiffsAndAstro avatar
TiffsAndAstro avatar
Im getting roughly (varies a little from night to night)  approximately  0.18(1.6). the first number is the rms accuracy? if so i think that's good enough for my gear? sw 72ed and canon 600d ?
Dan Watt avatar
Dan Watt avatar
I’ve noticed, oddly enough that my GTI guides better with more weight on it. Last outing I was running nearly 9 lbs of gear and guiding was around .8 rms. Usually in between 1-2 with the normal 5 lbs payload. 

I’ve also noticed that over the last year of using it regularly it’s gotten smoother and some issues with random dec spikes have gone away. Haven’t adjusted anything past initial backlash adjustments when I bought it. Almost as if it has to be “broken in”.
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Michael Ring avatar
Michael Ring avatar
TiffsAndAstro:
Im getting roughly (varies a little from night to night)  approximately  0.18(1.6). the first number is the rms accuracy? if so i think that's good enough for my gear? sw 72ed and canon 600d ?

Resolution of your  combo is 2.1 arcseconds per pixel and your guiding is 1.5 arcseconds per pixel so your effects of guiding to your stars will not be that significant when you do not see big spikes in your guiding graph.

Michael
TiffsAndAstro avatar
TiffsAndAstro avatar
Michael Ring:
TiffsAndAstro:
Im getting roughly (varies a little from night to night)  approximately  0.18(1.6). the first number is the rms accuracy? if so i think that's good enough for my gear? sw 72ed and canon 600d ?

Resolution of your  combo is 2.1 arcseconds per pixel and your guiding is 1.5 arcseconds per pixel so your effects of guiding to your stars will not be that significant when you do not see big spikes in your guiding graph.

Michael


Ty for this. I possibly have a little room for improvement. Reluctant to mess with the backlash screw though.
Tom Gray avatar
Tom Gray avatar
I have a 2i pro mount RA guiding only, so not really relevant to this forum but typically 1.10” on a good night with Stellarmate internal guider, which I find better than PHD2 which I used for years. I agree with short 0.5” guiding subs, and my rig is usually fully laden.
Javier avatar
Javier avatar
Can't thank you enough for this post and for sharing your configuration. What a game changer. I had found this earlier…. 😅