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1100GTO AE PHD2 Settings

#Guiding #Absolute_Encoders

Joe Erickson

I am loving my new Astro-Physics equipment (1100GTO AE, ATS 8x48 Tri-Pier, 130GT with Quad TCC & 13035FF). I received the 1100GTO AE in May but I am just now getting enough clear nights to learn how to use it.

I have PHD2 working better than my previous mounts but I see some 1100GTO users talking about better guiding numbers. I have not changed any of the default PHD2 settings yet.

My image trains are:

EdgeHD 14 (F11 – 3910mm FL) -> Litecrawler LR25 -> Optec Sagita OAG + QHY-5III 174M -> QHY 9x2 EFW -> QHY600M.
EdgeHD 14 (F8 – 2737mm FL) -> Celestron 0.7 Reducer -> Litecrawler LR25 -> Optec Sagita OAG + QHY-5III 174M -> QHY 9x2 EFW -> QHY600M.
AP 130 GT (F4.5 -> 585mm FL) -> Nitecrawler WR35 -> AP Quad TCC -> Optec Sagita OAG + QHY-5III 174M -> QHY 9x2 EFW -> QHY600M.
AP 130 GT (F6.7 -> 871mm FL) -> Nitecrawler WR35 -> AP 13035FF -> Optec Sagita OAG + QHY-5III 174M -> QHY 9x2 EFW -> QHY600M.

For software I use SGP, SharpCap, PHD2 and All Sky Plate Solver.

I have not used APCC because I have to set up in the backyard every time.

All of the above is new to me this year and a big upgrade from what I had before. The biggest surprise was how easy it is to polar align – no more fiddly small knobs!

Can anybody make recommendations regarding PHD2 settings and / or point me to a good source of information that would help me to make the best use of my 1100GTO AE?

Thank you.

Joe Erickson

Worsel

#79706

Joe

Congratulations on your SUBSTANTIAL upgrade!

RE: PHD2. Get involved with the PHD2 forum at https://groups.google.com/g/open-phd-guiding

Tips: Be meticulous about setting up your profile using the Wizard
Run a Baseline Assessment and Guiding Assistant

Read the Best Practices

Bryan

Brian Valente

#79707

Hi Joe

for a mount with absolute encoders like yours, you are going to want a different approach than what's outline in the baseline guiding document. (My experience is with the 1600 ae and i also wrote the PHD baseline guiding doc ).

you should still follow the baseline to the point where you run the guiding assistant and get your min moves, but you are going to want to do bump guiding, which is much less aggressive and does much better with absolute encoders.

Here are my observations

For guiding in PHD2 here are my settings (again, your min moves will be set by your guiding assistant run):

1x sidereal guiderate (which is the default, just don't mess with it)

4 second guiding exposure,

10 second "time lapse" (i.e., delay) between exposures.

lowpass 2 algorithm on both RA and DEC

medium aggressiveness (70 on scale from 1-100)

no backlash compensation

As I write this the guiding is around 0.25" total RMS, or about 1/2 a pixel on the CDK20/Proline 16803

i am still experimenting with aggressiveness: 50 seemed a little sluggish.

Perhaps just as informative, In my early testing using PHD2 guiding defaults of 2-3 second exposures ahd no delay, my guiding results were much worse on the order of 1.2-1.8" total RMS

Brian

Worsel

#79708

Brian

Thanks for the clarification on using the baseline with AE!

Bryan

Roland Christen

#79740

Hi all,

Some musings from my weeks of testing in Hawaii:

I just got back from Hawaii where I was able to spend a lot of time testing the guiding function of a 1600 encoder mount with an AP 175mm refractor. The tests were performed under various seeing conditions which ranged from 1.5 FWHM to 7.5 FWHM. Our observatory is located on the west slope of Kohala mountain, which is on the dry side of Hawaii Island.

The sharpest seeing occurred when the prevailing winds came up-slope from the ocean or were parallel to the shoreline. The worst came from trade winds that came over Kohala mountain and curled overhead. The worst seeing was so bad that Saturn was unrecognizable - it was just a boiling mess.

Over a period of 3 weeks I imaged just about every night and gathered a lot of data - both image data and autoguiding data. I also did a fair amount of unguided imaging. A couple of things stood out immediately. No matter what settings of guide exposure, time lapse and aggressiveness i used, the guiding results were almost 100% dependent on seeing. If the seeing was poor, the guide results were the same whether I used 2 second guide exposures or 10 second exposures. Putting long delay between exposures also did not change the results. A larger Min Move did help to prevent back and forth star chasing to some extent when the seeing was bad. But no matter what, when the seeing was 5 arc sec FWHM the guiding was consistently around 0.6 arc sec rms. When the seeing produced stars of 1.5 arc sec FWHM, the guiding at times went below 0.1 rms. In other words the stars were twinkling slightly but perfectly stationary and not doing the hula dance.

One thing i discovered was that for best guiding results the axes should be very well balanced. The gear mesh release mechanism of the 1600 gearbox allowed almost perfect balance with this large refractor. It is much more critical to set the Dec balance accurately than the RA axis. Reason is that unbalanced Dec causes static friction in the worm gear teeth, which makes Dec movements non-linear at the sub-arc sec level. The encoders do compensate and produce the final position very accurately, but the static friction introduces delay in getting there, overshoot, etc, which reduces the moment to moment positional accuracy. Bottom line - balance Dec as close as possible. RA is not affected by unbalance because it is always moving, so there is no static friction to contend with. The only thing I noticed was an increase in the sub-arc sec ripple in the sidereal drive rate. The more balanced the axis, the smoother the RA tracking.

I accumulated on the order of 300 sub exposures of the deep sky object that I was imaging (a mix of 10 minute and 20 minute sub exposures). Out of these only about 5 had non-round stars due to an occasional passing cloud. All stars were round, even when the seeing was an astonishing and atrocious 7.5 arc seconds (seeing is a judge of star size in FWHM, guiding is a judge of the guide star motions in arc sec rms). So, even in poor seeing the dual encoders operated equally in both axes to keep the scope pointed properly, even though the guide star was pulsing like an amoeba. What might surprise long-time imagers is that I plan to use very frame in the final image. I will not be throwing out any of the subs, even though they contain bloated stars.

I did do some unguided imaging using the drift model in the keypad. I was operating at approximately 1000mm focal length and could do up to 20 minute subs with round stars. I used 8 points along the object path, starting from 4 hours in the east with scope under the mount, to 3 hours past the meridian in the west. The object was low enough to the south to allow the scope to start underneath with counterweight up. I experimented with a mix of unguided and nudge guiding with very low aggression. The problem with low aggression is when you are dithering it takes a long time for the guide star to come back to zero. Same is true if you are using long exposure times or long delay times between guide exposures. You have to allow for long guider settling time, and that eats into your imaging time.

The scope itself performed beautifully with very predictable focus with temperature. Even though the lens is a 175mm triplet and the daytime observatory was between 95 - 98 degree F during the day, once the roof was retracted and the sun set, the scope acclimated within the hour to 75 degree air temp. It produced sharp images as soon as it got dark enough to image. I refocused perhaps twice or 3 times during the night until just before dawn when the temp bottomed out at 68F. The nice thing about this triplet design was that the focus did not change between all my narrowband filters.

For those who say that large airspaced triplet lenses have long cooling/settling times, I did not experience that with this scope. But then maybe my observing conditions are not as extreme as some people experience? The AP 175 Triplet lens has thinner lens elements than is normally used. This required a lot of careful polishing at very low pressures when I fabricated them. And that cost a lot of time and money, but the results are worth it. The lens is made with 2 elements of BSL7 and one with S-FPL53, both Ohara glasses and both outstanding quality wise. Why is that important? Because what you get with BSL7 is extremely high internal homogeneity. Some people are enamored with Lanthanum mating elements, but these glass types were never intended for objective grade lens applications and do not have the high internal homogeneity of borosilicate crown glass. Lanthanum is also much heavier and retains heat with longer thermal settling down times.

Unfortunately S-FPL53 is no longer available but fortunately FPL55 and Hoya FCD100 can be used with similar performance using the same borosilicate crown mating elements.

I will do some more postings on mount and scope performance once I get a chance to analyze the data.

Rolando

Show quoted text

-----Original Message-----
From: Brian Valente <bvalente@...>
To: main@ap-gto.groups.io
Sent: Thu, Jul 29, 2021 8:29 pm
Subject: Re: [ap-gto] 1100GTO AE PHD2 Settings #Guiding #Absolute_Encoders #Guiding

Here are my observations

For guiding in PHD2 here are my settings (again, your min moves will be set by your guiding assistant run):

1x sidereal guiderate (which is the default, just don't mess with it)

4 second guiding exposure,

10 second "time lapse" (i.e., delay) between exposures.

lowpass 2 algorithm on both RA and DEC

medium aggressiveness (70 on scale from 1-100)

no backlash compensation

As I write this the guiding is around 0.25" total RMS, or about 1/2 a pixel on the CDK20/Proline 16803

i am still experimenting with aggressiveness: 50 seemed a little sluggish.

Perhaps just as informative, In my early testing using PHD2 guiding defaults of 2-3 second exposures ahd no delay, my guiding results were much worse on the order of 1.2-1.8" total RMS

Brian

--
Roland Christen
Astro-Physics

skester@...

#79750

Roland,

I have a non AE 1100GTO. Based on supposed 'best practices', I have always left a slight imbalance of East heavy in RA, and 'camera heavy' in Dec. However this practice was likely intended for mounts with considerably more backlash than an AP mount. If I'm interpreting your post correctly, Dec should be as close to perfectly balanced as possible. Does that hold for both AE and non-AE mounts? Also should I continue to use slightly East heavy in RA, or should that be as close to perfectly balanced as well?

Thanks,
Scott

Roland Christen

#79753

Even for non-encoder 1100 mounts you should balance both RA and Dec. No need for east heavy on RA. Both axes have spring loaded worm mesh, so you won't gain anything from unbalance. Dec unbalance will produce more delay in reversal due to higher static friction, so again it is best to balance the Dec axis well.

Rolando

Show quoted text

-----Original Message-----
From: skester@...
To: main@ap-gto.groups.io
Sent: Sat, Jul 31, 2021 10:55 am
Subject: Re: [ap-gto] 1100GTO AE PHD2 Settings #Guiding #Absolute_Encoders #Guiding

--
Roland Christen
Astro-Physics

Eric Dreher <ericpdreher@...>

#79754

Roland, that begs the question about other models. With my 2017 Mach1GTO, I release the gearboxes, balancing RA as best I can, with DEC being a different animal. On Pier East, Dec is just about spot-on, while Pier West is camera-heavy. At times I do try to split the difference, but wonder if I'm really doing any good.

Last week's guiding had PHD2 RA at 0.25", Dec at 0.14", and an RMS of 0.28". It seems like it doesn't get much better. I'd appreciate your input, and thank you.

Roland Christen

#79755

If the guiding is good, then that's all that matters. Perfect balance is not expected, just get it as close as you can.

Rolando

Show quoted text

-----Original Message-----
From: Eric Dreher <ericpdreher@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 31, 2021 1:09 pm
Subject: Re: [ap-gto] 1100GTO AE PHD2 Settings #Guiding #Absolute_Encoders #Guiding

--
Roland Christen
Astro-Physics

Andrew Jones

#79825

Hi Roland.

I really appreciate these detailed After Action Reports. 😊 These reports provide useful insight for those of us still learning the art/science of astrophotography and how to get the best experience from our AP Mounts. I recently upgraded my Mach1 to a 1100 AEL. I am still in the process of getting it setup in my observatory (waiting for some cooler weather here in Texas), but once setup these reports will be useful references to help ensure I am able to get everything setup and calibrated correctly.

The info you provided about DEC balance is very interesting. I never really paid that much attention to the DEC balance. I would balance my TEC 140 close to its imaging configuration when putting the scope on the mount in my observatory, but then I really didn’t mess with again. I just weighed my camera/FW combo and it is almost 5lbs. Combined with 85mm of back focus for the TEC 140, I would guess this creates a fairly substantial moment arm on the DEC axis (similar to the recommendation to avoid putting counter weights as the end of the counter weight bar vs. adding more weights). This moment arm could help explain why I always struggled with guiding with my Mach1, particularly on the DEC axis. PEMPro indicated my polar alignment was within 1-2 arc min on both axis, so I don’t think it is an issue with alignment. Your worse RMS of 0.6 arc sec would be a dream for me. On a typical night, I am lucky if I could keep the RMS below 1 arc sec using PHD2. Based on your observation, I will be pay more attention to the DEC balance and balance more frequently for different temperature ranges and see if that helps with my guiding.

I always pay close attention to your experiences with PHD2. As mentioned, I have struggled with guiding. It is helpful to read your(and others) observations and experience with PHD2 and what settings they were using. I wish there was one universal combination of settings in PHD2 that would work in all conditions, but that probably unlikely. It helpful thou to read what settings are working for other AP mount owners that I can try with my own setup, at least as a starting point. I just saved a note with the settings Brian Valente posted earlier and intend to give those a try once I get everything setup.

I have a couple of questions if you don’t mind.

I can balance the scope at the begging of the night close to my last focus position, but as soon as I run auto focus obviously the moment arm will change somewhat. Where I image, it is not uncommon to see a 10°F change in temperature during a given imaging session. I refocus ever 1.5° change in temperature. To avoid the static friction issue on the DEC axis, is it necessary to rebalance during an imaging session or are the changes to the moment arm due to refocusing insufficient to cause the static friction issue you discussed? In other words, how much out of balance can be tolerated due to refocusing before we should be concerned about static friction?

Kind of unrelated question, but how do you determine what your Seeing is during an imaging session? Are you just using the FWHM as reported by your imaging software or do you have another method of determine what the seeing is on a giving night? Based on what your report regarding the impact Seeing has on guiding, it would be good to have a easy way to determine what the Seeing conditions are for a given night so we can adjust our guiding expectations accordingly. I know there are Sky Quality Meters as well as Clear Sky Charts online. I was just curious if you use one of these tools to determine your seeing or if you have another method. Probably a stupid question, but hey I am still learning…

Clear Skies,

Andrew J

Linwood Ferguson

#79827

@Andrew Jones wrote:

Kind of unrelated question, but how do you determine what your Seeing is during an imaging session? Are you just using the FWHM as reported by your imaging software or do you have another method of determine what the seeing is on a giving night?

I’m also interested, and in particular if there’s an expected relationship to something like total RMS error in PHD2.

I’ve had all of two nights with the AP1100 and am just delighted with its guiding performance. I’m seeing around 0.25 to 0.30” total RMS consistently and nice round stars, and low FWHM in the images.

So a large part of me says ‘take it and be happy’, but there’s that nagging section that says “is it seeing limited, or can I do better”. How do you know?

But even that nagging part of me is really happy… I looked at my eccentricity from the luminance shots, 120s each, and they were not only almost perfect, but almost a straight line – very consistent shot after shot (I have some backfocus issues in the corners I suspect is why they are not better still).

But to his larger point – yes please, those who know what you are doing, keep the examples and suggestions coming. Lots to learn!

Andrew Jones

#79828

Hi Roland.

FYI. I think the manual needs to be updated. The manual indicates that a balance offset is recommend on both axis

From Page 27 of the 1100 GTO Manual:

Precision Balancing Remember that dangling cables will dramatically change balance and create guiding problems, so you’ll want to be sure that all cables are carefully secured and not dragging before you proceed with balancing. Ensure that your focuser is in its focused position, the dew shield extended and the dust cap removed. The following three recommendations will increase guiding performance.

Slightly offset balance to the counterweight side of the R.A. axis. When the axis is perfectly balanced horizontally, then offset the weight just enough to start motion slightly downward on the counterweight side.
Slightly offset balance to the camera side of the Dec. axis. When the axis is perfectly balanced horizontally, then offset the scope just enough to start motion slightly do
The counterweights should ride high on the counterweight shaft. It is best to add counterweights and slide them to the top of the shaft with the heaviest at the top and then use the smallest weight to perform the precision balancing. The reason for this is called “Inertial Moment Arm”. Sliding less weight down the shaft will balance the scope, but will greatly increase the moment arm force; that is to say, it will require a much greater torque to start the axis rotating. (Think of a tightrope walker using a long rod to stabilize his balance.) This is a very important consideration when you are trying to do precise guiding

Pete Mumbower

#79830

I agree lots to learn for the for the newer mount owners coming from "non-premium" mounts. I know there is tons of nuggets of info on best practices for both AE and non-AE 1100/1600 mounts with PHD around. But does anyone have a best practices collection? For myself coming from a CGE-Pro, I was so use to 2s PHD exposures. Last night I switched to 4s for the heck of it and the RMS improved noticeably. I need to remember my non-AE 1100GTO behaves totally different. I also need to go out and balance both axis as Rolando suggested a couple days ago.

Roland Christen

#79831

Refocusing does not require re-balancing. I would not worry about it.

Seeing can be judged easily by turning tracking corrections off and watching the star excursions on the tracking graph in Dec. If the star jumps around +- 1.5 arc seconds, then your seeing is 3 arc sec P-P and you can then set your Min Move to that level. Seeing will vary somewhat with altitude, so if you image an object near the zenith, the seeing might be twice as good as it would be if the object is at 30 to 45 degrees above the horizon.

Rolando

Show quoted text

-----Original Message-----
From: Andrew Jones via groups.io <andrew.jones@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Mon, Aug 2, 2021 12:35 pm
Subject: Re: [ap-gto] 1100GTO AE PHD2 Settings

Hi Roland.

I have a couple of questions if you don’t mind.

I can balance the scope at the begging of the night close to my last focus position, but as soon as I run auto focus obviously the moment arm will change somewhat. Where I image, it is not uncommon to see a 10°F change in temperature during a given imaging session. I refocus ever 1.5° change in temperature. To avoid the static friction issue on the DEC axis, is it necessary to rebalance during an imaging session or are the changes to the moment arm due to refocusing insufficient to cause the static friction issue you discussed? In other words, how much out of balance can be tolerated due to refocusing before we should be concerned about static friction?

Kind of unrelated question, but how do you determine what your Seeing is during an imaging session? Are you just using the FWHM as reported by your imaging software or do you have another method of determine what the seeing is on a giving night? Based on what your report regarding the impact Seeing has on guiding, it would be good to have a easy way to determine what the Seeing conditions are for a given night so we can adjust our guiding expectations accordingly. I know there are Sky Quality Meters as well as Clear Sky Charts online. I was just curious if you use one of these tools to determine your seeing or if you have another method. Probably a stupid question, but hey I am still learning…

Clear Skies,

Andrew J

--
Roland Christen
Astro-Physics

Brian Valente

#79832

Hi Pete

there is a doc PHD offers on best practices:

https://openphdguiding.org/phd2-best-practices/

One other thing I'd suggest is doing a baseline guiding setup, which can be done by following this doc (this is what we use in the PHD support forums) - this is a more recent best practice we recommend in addition to the above doc:

https://www.dropbox.com/s/zrf0au7jaisvt85/How%20to%20create%20a%20baseline%20for%20guiding%20results%20using%20OpenPHD2.pdf?dl=0

This starts with entering appropriate equipment settings and using default algorithms, and then using the built-in guiding assistant will get you a solid starting point and avoid common mistakes that can happen when transitioning between mounts.

better behaved mounts can perform better (i.e., reduce seeing related noise) with longer exposures, but of course ymmv

ae vs non ae mounts are very different in terms of guiding, so they really are two different approaches.

hth

Brian

Show quoted text

On Mon, Aug 2, 2021 at 10:58 AM Pete Mumbower <pmumbower@...> wrote:

I agree lots to learn for the for the newer mount owners coming from "non-premium" mounts. I know there is tons of nuggets of info on best practices for both AE and non-AE 1100/1600 mounts with PHD around. But does anyone have a best practices collection? For myself coming from a CGE-Pro, I was so use to 2s PHD exposures. Last night I switched to 4s for the heck of it and the RMS improved noticeably. I need to remember my non-AE 1100GTO behaves totally different. I also need to go out and balance both axis as Rolando suggested a couple days ago.

Brian

Brian Valente

portfolio brianvalentephotography.com

Pete Mumbower

#79833

Thanks for the links for the docs Brian. I will go thru those to see if anything has changed in recent years. I have used PHD for the last 10yrs (I think) but I am always learning new things. More just trying to undo how I use to think with my Celestron mount and trust that the A-P can handle longer guide exposures to smooth our seeing noise. Heck I just love the next non-existent backlash in the DEC!

Sorry to the OP, not trying to hijack the thread. I will start a new post if I feel the need for one.

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