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Guiding with ASI Air #tracking

Devesh Pande
 

I was imaging the Rosette Nubula tonight. I wanted to dither my DSLR every frame but I realized the mount is taking too long to settle down post Dithering. So much so that my next sub gets completely wasted with a bit of trails. I have also seen this longer settling time after I calibrate and start guiding. The graph sometimes goes as high as 100 arc sec in RA/Dec and then eventually settles down to 2 arc sec or thereabouts. Am I missing something in guiding? I am using multi star guiding. I use 70% aggressiveness on both RA and DEC and exposure of 2 sec. I am using an Svbony 30mm guidescope with focal length of 120mm and an ASI462MC as autoguider. Using defaults for calibration step and settle times from ASI air (2000 ms).

This is the first time I am using a goto and an autoguider so forgive my naivety.

Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
Billy Beckett
 

I have heard of people using bin 2 on the guide camera. They say it helps. I am going to try it my next time out to try for better guiding. You might want to try that next time and see how it works for you.

 

Billy Beckett.

 

From: MAIN@ESPMC-Eight.groups.io <MAIN@ESPMC-Eight.groups.io> On Behalf Of Devesh Pande
Sent: Sunday, January 16, 2022 2:41 AM
To: MAIN@ESPMC-Eight.groups.io
Subject: [ESPMC-Eight] Guiding with ASI Air #tracking

 

I was imaging the Rosette Nubula tonight. I wanted to dither my DSLR every frame but I realized the mount is taking too long to settle down post Dithering. So much so that my next sub gets completely wasted with a bit of trails. I have also seen this longer settling time after I calibrate and start guiding. The graph sometimes goes as high as 100 arc sec in RA/Dec and then eventually settles down to 2 arc sec or thereabouts. Am I missing something in guiding? I am using multi star guiding. I use 70% aggressiveness on both RA and DEC and exposure of 2 sec. I am using an Svbony 30mm guidescope with focal length of 120mm and an ASI462MC as autoguider. Using defaults for calibration step and settle times from ASI air (2000 ms).

This is the first time I am using a goto and an autoguider so forgive my naivety.

Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR

Apertura 1X field flattner

ZWO ASI Air

ZWO ASI472MC
NikonD5500a
Celestron C8

Optolong Lpro

Optolong Lextreme

Bortle 7


--
Billy Beckett

ES 80mm triplet refractor
ES EXOS II PMC-Eight mount
Meade StarNavigator 130mm Newton
Celestron 8” Newton with CGEMII and AVX mounts
ES 10" Truss Dob
ZWO ASI294MC-Pro & ASI120MM-mini
Corpus Christi, Texas
Devesh Pande
 

I did use bin2 guiding yesterday. Problem is not the error. Problem is that the mount takes a lot of time to settle down post Dithering or calibrating.
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
Wes Mcdonald
 

Devesh 

I always thought the exos2 was not something I wanted to dither, especially in dec.   After using it to image my view is that it is just not up to it mechanically.  However, if you use Nina (other apps might also do this) you can set a delay after dither before starting the next exposure.  

My guess is the dither performance is limited by the backlash in dec, which can be pretty large even when tuned up.   Ra backlash ordinarily not an issue as that axis, under normal guiding, never reverses.  When dithering it might, I am not sure.   Maybe not.  But with backlash it’s just gonna take time for the mount to settle down into sidereal rate tracking even if the thing isn’t oscillating.  

If the mount is heavily loaded and it is oscillating, settling time can also be affected but I have not tried to characterize that, it is just canon (dogma? Common knowledge? Urban legend?).  It makes sense however as the period of oscillator of a spring mass system is proportional to the square root of mass.  So on first principles, with lots of hand waving, heavier loads will oscillate with larger amplitudes. Now the time it takes a spring mass system to “ring down” or settle is also dependent on the damping or friction applied to the moving mass.  Intuitively you can probably see that the more friction one has the quicker an oscillation will die out.  

In my view the telescope is a mass on a twisting member which has a spring constant that applies when twisted.  And the damping is basically that offered by the air pressure against the moving tube.  So imagine a ruler extended over the edge of a table that you hold tight against the table with one hand and pluck suspended end.  The ruler vibrates a long time as the energy you put into it by bending it is dissipated in losses in the vibrating member and by work the ruler is doing against the air as it moves up and down.   To me that is what the dominant vibrational mode of the telescope mass is like.  Every member of the telescope mount subject to bending when a force is applied to the structure will store energy that must be released and dissipated. Tbh Sigh

So heavier masses will have larger excursions when you displace them with what amounts to pluck from a dither, and the rate of decay is thus, for equal damping, gonna be less, ie it’s gonna take longer to stop ringing.  

More or less

 Bottom line is set a long enough delay after a dither to allow everything to settle down prior to imaging.  

Wes





--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100, ESG11
ES ED 127+MoonLite Focuser, 10" LX200GPS+ MoonLite focuser+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified, ASI071 cooled OSC, ASI MM290 guide camera
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired
Dino Monaco
 

Hi Devesh,

Im glad that you posted this particular issue with the auto guiding and the EXOS 2. Reason is I had exactly experienced the same issue a week ago. In fact, I was photographing the Rosetta Nebula as well. My scope was the ES102CF with the Orion 60mm guide scope piggybacked on top and controlled by the asiar plus.
So, I began the session pointing eastward. And just like you, I observed frequent long settling times after dithering and high RMS values, mainly in RA. But I continued with the session anyway thinking perhaps my alignment wasn’t perfect because I kind of rushed it due to the extreme cold we’re experiencing. ~12 F.
Now, as the night proceeded with the subpar guiding, I noted that the rig was ready for a meridian flip. So I decided to go out and watch the process. As the mound began the flipping, it suddenly released that loud ratcheting sound from the stepper motor. Again I think it was mainly in RA but not sure. At that point I halted the session , and manually flipped the scope over to the other side. Next, I went through the routine Asiar guiding routines, and to my surprise I was now witnessing sub-arc second guiding the rest of the night. This was now confusing. Later I pointed the scope to Alderamin which is a northerly star. Again dub arc second guiding. Hmmmm🤔

I’m adding to this thread so that we can troubleshoot the problem by sharing more experiences and providing each other additional clues.

From my experience, two things are in my mind but I could be wrong.
1. Was I not perfectly balanced they caused the poor guiding values?
2. Perhaps the extreme cold ‘froze’ up the gear lubricant and strained the RA drive when in East position? 
At this point Im waiting, for the next clear night to try working on this issue further. 
What I do not want to do is tearing my 2 month old mount apart to hyper tune the gearing and apply some superior grease. Well, not at this time anyway.
I hope this long winded story helps you in your troubleshooting journey. 

Dino

 

 
Captain Haddock
 

Parag,

So if this really your first time autoguiding, I suggest you proceed incrementally. Using autoguiding and adding dithering all at once complicates troubleshooting in case something does not go as expected. 

The tracking accuracy and thus even the autoguided tracking will be somewhat a function of the direction of the mount. I have not tried dithering so I cannot comme t on whether dithering performance or benefits are similarly directional.

The other reason for my suggestion is to check whether or how accurate autoguiding/dithering you need for your equipment and target. I am new to autoguiding myself, but have so far found that (a) there is a difference of what I think I should be able to do vs what I actually need to do (ROI on a new process) and (b) having one new thing introduced at a time makes troubleshooting or fine tuning my process (or expectations) easier.

On Sun, Jan 16, 2022, 11:47 AM Dino Monaco via groups.io <Dinomonaco=me.com@groups.io> wrote:

Hi Devesh,

Im glad that you posted this particular issue with the auto guiding and the EXOS 2. Reason is I had exactly experienced the same issue a week ago. In fact, I was photographing the Rosetta Nebula as well. My scope was the ES102CF with the Orion 60mm guide scope piggybacked on top and controlled by the asiar plus.
So, I began the session pointing eastward. And just like you, I observed frequent long settling times after dithering and high RMS values, mainly in RA. But I continued with the session anyway thinking perhaps my alignment wasn’t perfect because I kind of rushed it due to the extreme cold we’re experiencing. ~12 F.
Now, as the night proceeded with the subpar guiding, I noted that the rig was ready for a meridian flip. So I decided to go out and watch the process. As the mound began the flipping, it suddenly released that loud ratcheting sound from the stepper motor. Again I think it was mainly in RA but not sure. At that point I halted the session , and manually flipped the scope over to the other side. Next, I went through the routine Asiar guiding routines, and to my surprise I was now witnessing sub-arc second guiding the rest of the night. This was now confusing. Later I pointed the scope to Alderamin which is a northerly star. Again dub arc second guiding. Hmmmm🤔

I’m adding to this thread so that we can troubleshoot the problem by sharing more experiences and providing each other additional clues.

From my experience, two things are in my mind but I could be wrong.
1. Was I not perfectly balanced they caused the poor guiding values?
2. Perhaps the extreme cold ‘froze’ up the gear lubricant and strained the RA drive when in East position? 
At this point Im waiting, for the next clear night to try working on this issue further. 
What I do not want to do is tearing my 2 month old mount apart to hyper tune the gearing and apply some superior grease. Well, not at this time anyway.
I hope this long winded story helps you in your troubleshooting journey. 

Dino

 

 
Captain Haddock
 

Hehe, sorry I meant Devesh, not Parag!


On Sun, Jan 16, 2022, 12:30 PM Amit Shesh <amitshesh@...> wrote:
Parag,

So if this really your first time autoguiding, I suggest you proceed incrementally. Using autoguiding and adding dithering all at once complicates troubleshooting in case something does not go as expected. 

The tracking accuracy and thus even the autoguided tracking will be somewhat a function of the direction of the mount. I have not tried dithering so I cannot comme t on whether dithering performance or benefits are similarly directional.

The other reason for my suggestion is to check whether or how accurate autoguiding/dithering you need for your equipment and target. I am new to autoguiding myself, but have so far found that (a) there is a difference of what I think I should be able to do vs what I actually need to do (ROI on a new process) and (b) having one new thing introduced at a time makes troubleshooting or fine tuning my process (or expectations) easier.

On Sun, Jan 16, 2022, 11:47 AM Dino Monaco via groups.io <Dinomonaco=me.com@groups.io> wrote:

Hi Devesh,

Im glad that you posted this particular issue with the auto guiding and the EXOS 2. Reason is I had exactly experienced the same issue a week ago. In fact, I was photographing the Rosetta Nebula as well. My scope was the ES102CF with the Orion 60mm guide scope piggybacked on top and controlled by the asiar plus.
So, I began the session pointing eastward. And just like you, I observed frequent long settling times after dithering and high RMS values, mainly in RA. But I continued with the session anyway thinking perhaps my alignment wasn’t perfect because I kind of rushed it due to the extreme cold we’re experiencing. ~12 F.
Now, as the night proceeded with the subpar guiding, I noted that the rig was ready for a meridian flip. So I decided to go out and watch the process. As the mound began the flipping, it suddenly released that loud ratcheting sound from the stepper motor. Again I think it was mainly in RA but not sure. At that point I halted the session , and manually flipped the scope over to the other side. Next, I went through the routine Asiar guiding routines, and to my surprise I was now witnessing sub-arc second guiding the rest of the night. This was now confusing. Later I pointed the scope to Alderamin which is a northerly star. Again dub arc second guiding. Hmmmm🤔

I’m adding to this thread so that we can troubleshoot the problem by sharing more experiences and providing each other additional clues.

From my experience, two things are in my mind but I could be wrong.
1. Was I not perfectly balanced they caused the poor guiding values?
2. Perhaps the extreme cold ‘froze’ up the gear lubricant and strained the RA drive when in East position? 
At this point Im waiting, for the next clear night to try working on this issue further. 
What I do not want to do is tearing my 2 month old mount apart to hyper tune the gearing and apply some superior grease. Well, not at this time anyway.
I hope this long winded story helps you in your troubleshooting journey. 

Dino

 

 
BobH
 

Welcome Devesh! The Rosette is my favorite Winter object, and was my first test object when I got my EXOS-II. I'm also imaging with a wide-field kit, not all that different from yours. I'm using PHD2 for guiding (I believe the ASIAIR uses a variant of this software for its guiding), and SharpCap for imaging control.

For dithering:
  • Many software packages provide one or more useful controls over dithering, especially helpful if your rig takes a long time to settle: for example, in my combo, I can set both a pixel stability-target, and min/max time-limits to settle. With my EXOS rig, the defaults proved sufficient, but with a 20+ year-old predecessor to this mount design, I had to increase the max time, otherwise I'd have the same problem you experienced - a new image starting before the scope had fully settled.
  • When shooting shorter exposures, say 90-seconds or less, I usually only dither every 5-10 subs. Dr. Robin Glover, author of SharpCap, suggested dithering was often a net negative when taking short exposures - the idle-time spent waiting for the mount to settle would be better spent imaging without dither. Just be sure to include the necessary calibration frames (darks...) in your workflow. When shooting 10 minute and up subs, I dither every sub, as the overhead is not too great. In your sky, 10 minute and up subs would be useful with dual narrow-band filters such as your L-Extreme. However, if shooting with a milder sky-glow filter, such as an L-Pro or Baader NeoD, optimal exposures are likely to be closer to 30-90 seconds. SharpCap (the paid-version), will calculate the optimum for you, based on measurements of your sensor's characteristics (noise, gain, linearity...) and test exposures of your imaging zone. In a light-polluted zone, optimal lies closer to more subs of a shorter duration - with narrow-band filters, or true dark skies, you can begin to take advantage of fewer but longer longer subs. Dr. Glover pointed out that in a common suburban sky, capturing subs without an aggressive filter, subs of around 15 seconds are about where diminishing returns dominate.
Long settling time:
  • I've not experienced anything close to the excursions you're describing. Mounts of this general class are notorious for having a large amount of backlash in one or both axis. In RA, one common trick is to balance the mount to be slightly heavy on the east-side of the axis. Under common conditions, the RA drive will seldom/never need to reverse, only slow down if an easterly correction is required, thereby hiding any backlash in this axis. However, if you are dithering, that may cause an actual reverse in RA movement direction, to make a significant eastward shift, and this could expose an RA backlash problem if one exists. One can also slightly off-balance in DEC, and select the PHD2 DEC algorithm designed to minimize direction changes in DEC, "Resist Switch". Some folks will slightly de-tune their polar alignment, to introduce an intentional drift in DEC that can then be corrected by guiding with "pushes" in a single direction.
  • With this mount and its predecessor (Meade LXD55), I got my best results using the "Predictive PEC" algorithm for RA, "Resist Switch" for DEC. "Hysteresis" for RA generally also performed well for me, but slightly off from the PEC algorithm. Note that when using Predictive PEC, it takes a while to establish the intrinsic guiding error - 10 minutes or more with the EXOS-II. For me, guiding is not a disaster while its calculating the PEC curve, but sometimes less than ideal. I use that time to fine-tune focus, calculate exposures... Your results will vary.
Other Guiding:
  • If ASIAir exposes the "Guiding Assistant" feature of PHD2, give it a try. This feature temporarily disables sending guide-pulses, while watching how the mount behaves. You can run it as long as you like, a few minutes is typical. It assesses drift, polar alignment accuracy..., and makes recommendations for tweaks to your guiding parameters, guide exposure length, and so forth. This is often a better approach than directly altering the numerous guiding algorithm parameters, which often interact in complex ways and can take you far afield. The Guiding Assistant can also do a thorough analysis of backlash for both axis, which gives you real data to help assess if there is a mechanical problem.
  • I'm not familiar with the "ASI472MC" listed in your profile. Personally, I've never tried using a color camera for guiding, always stuck with mono for that duty. Without evidence, I'm a bit suspicious. PHD2 is quite capable of calculating sub-pixel position information (0.1 - 0.3 pixel accuracy is typical for me.) This depends on processing guide-star data that is smeared over multiple pixels (focus, diffraction, seeing...). I'm wondering what the effect of introducing the Bayer matrix into the light-path would be. For example, if a guide star were reddish, would alterations in apparent brightness as that star's image moved across the RGB filters introduce meaningful noise/error into the position calculations? I have no empirical evidence for this, just a gut reaction. While I'm clear on binning in a mono-scenario, I don't have any idea what happens if you try that with a color sensor. Every time I've asked, I've been given a different explanation, or am met with "I have no idea..." With a mono-guider, multi-star guiding through a dedicated short FL guide scope, I'd leave binning off, unless you cannot identify enough stars for guiding while keeping exposure lengths/gain/noise within acceptable limits. Binning will improve your sensitivity and SNR, at a loss of precision.
  • Sub 2" RMS may prove quite adequate for your imaging rig, which is on the wide-field side of things. Check out a sub taken while the mount is stable, holding <2"RMS. You may find the stars are totally acceptable at the pixel-peeking level. My setup is slightly wider field than yours and under-sampled (larger pixels than your imaging camera), and for deep-sky imaging, 2"RMS is absolutely invisible under normal seeing. Your rig is somewhat more sensitive, with a potential finer resolution - but worth checking if there is an actual impact. Note, this is while "stable" - not if still moving around from a dither, or undertaking a 100" walk-about!
  • I've noticed that guiding accuracy for my EXOS-II is dependent on where I'm pointing. When imaging to the South, with the target still East of the meridian, my scope is on the West side of the mount, pointing East. I'll get my worst tracking, about 1 guider-pixel RMS (0.5 pixels on the imaging sensor.) About 3/4 of that error will be in the RA. But if I then shift northward, say to M81 after imaging the Rosette, without recalibration, my RMS will improve to around 0.6", sometimes better. The RA settles down to the same or better as the DEC, which also improves somewhat. This was absolutely repeatable for me over 3 successive nights, and 8-9 tests. I haven't figured this out yet, but I'm interested in what it might mean.
Best luck!

--
Mounts: 1980's Celestron "EQ" Fork; Meade LXD55; Skywatcher Star Tracker; EXOS-II PMC-8
Optics: C-11; Meade AR5 Achromat Refractor; RedCat51; Various DSLR lenses
Cameras: ASI071 MC (DSO imaging); ASI290MM (guiding); ASI178MC (Planetary/Lunar imaging); Sony A700 DSLR
Computers: Win10Pro Laptop (ASCOM ecosystem, at-the-mount); RPi4b (INDI, on-the-scope); Win10Pro Workstation (networked remote control); Galaxy S5 Tablet
Misc: Pegasus power Pocket Adv (power mgmt, USB hub, dew/env); ZWO EAF; ZWO 1-Filter Drawer
Imaging SW: Stellarmate (low-power remote); SharpCap 4.0 Pro/Astap; PHD2; Stellarium; ASCOM 6.5.1
Processing: PixInsight; DSS; GIMP; F4W2HDU; AutoStakkert; RegiStax6
Wish-list: 5-inch class APO; Losmandy G-11; RASA-11?
Wes Mcdonald
 

Bob

I think it means the position error on the guide camera when the ra is rotated when looking near the pole is far smaller than when looking about anywhere else.  If you want to see this demonstrated start your mount pointing north and tell poth to move it 30’. It will rotate in ra nearly 90 degrees.  

Generally I have better guiding north ESY and north west than anywhere else.  At least I think I did.  Haven’t done much in a long while.

Wes

--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100, ESG11
ES ED 127+MoonLite Focuser, 10" LX200GPS+ MoonLite focuser+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified, ASI071 cooled OSC, ASI MM290 guide camera
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired
BobH
 

Ah, thanks Wes, that makes sense. I noticed another respondent mentioned they had varying guiding results against the same southern target, comparing pre to post meridian flip performance. I'll have to check that out someday. For southerly targets, I seldom flip to a westward-pointing scope due to obstructions - not worth a flip to get <30 minutes more exposure before the trees have their say. And I've never done it yet with the EXOS. It will be interesting.

First my neck of the woods has to figure out where we put the stars these last few months - someone, somewhere, bought a new piece of AP gear and Mother Nature took notice...

--
Mounts: 1980's Celestron "EQ" Fork; Meade LXD55; Skywatcher Star Tracker; EXOS-II PMC-8
Optics: C-11; Meade AR5 Achromat Refractor; RedCat51; Various DSLR lenses
Cameras: ASI071 MC (DSO imaging); ASI290MM (guiding); ASI178MC (Planetary/Lunar imaging); Sony A700 DSLR
Computers: Win10Pro Laptop (ASCOM ecosystem, at-the-mount); RPi4b (INDI, on-the-scope); Win10Pro Workstation (networked remote control); Galaxy S5 Tablet
Misc: Pegasus power Pocket Adv (power mgmt, USB hub, dew/env); ZWO EAF; ZWO 1-Filter Drawer
Imaging SW: Stellarmate (low-power remote); SharpCap 4.0 Pro/Astap; PHD2; Stellarium; ASCOM 6.5.1
Processing: PixInsight; DSS; GIMP; F4W2HDU; AutoStakkert; RegiStax6
Wish-list: 5-inch class APO; Losmandy G-11; RASA-11?
Devesh Pande
 

Hello Dino and Bob,

Thanks a lot for your suggestions.

I haven't tried east heavy setup yet. I read about a 'string and weight' method which I am planning to adopt to have slight eastward imbalance. 

Bob,

Unfortunately the 'resist switch' option you mentioned on the DEC is not available with ASI Air. I don't not have a PC to try PHD2 guiding. ASI air really makes my job easy with regards to PA and go-to functionality and hence I ahve not ventured into PC. 

Last night I was imaging the flaming star nebula and I was getting about 2 RMS total error. Most of the error was coming from RA as I had a good PA (withing 1.3 arc sec. Not sure if I need to be any lower). DEC was around 0.8 RMS. I have never got any better numbers than these frankly speaking yet my stars are nice and round. May be it is because of my widefield setup.

I did try dithering last night but had similar observations. Very long settling times (Again total RMS was about 2 arc sec). I waited about 60 s for the mount to settle down yet the RMS values were high. I also noticed that for DEC, I was doing North corrections before dither and after dithering, RA settled pretty quickly but DEC went to about 40 arc sec and was having trouble settling down. I have also seen that the auto DEC corrections don't really work and I adjust either north/south based on the corrections graph. Dithering in DEC will change the north/south correction and perhaps that's why this number goes up?

I am still very new to this so do not fully understand whats going on.

Dino,

Did you have a chance to try this again?

Captain Haddock,

Thanks for your inputs. For my Rosette nebula, I did end up not dithering at all. I have decided to take things slow and learn one thing at a time.

Thanks,
Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
Captain Haddock
 

I would be interested in the RA guiding error too. I have the same experience, but my error is often larger than 2.5 arc seconds (the default I am using).

@devesh: what is your polar alignment error? I have it to less than 2 arc minutes, but the PA error just oscillates if I try to tweak it further. I am using stellarmate OS on RPI 4 and use Ekos for polar alignment, guiding (ekos guider) and plate solving (go-to).

On Sat, Jan 22, 2022, 10:20 AM Devesh Pande <deveshp1@...> wrote:
Hello Dino and Bob,

Thanks a lot for your suggestions.

I haven't tried east heavy setup yet. I read about a 'string and weight' method which I am planning to adopt to have slight eastward imbalance. 

Bob,

Unfortunately the 'resist switch' option you mentioned on the DEC is not available with ASI Air. I don't not have a PC to try PHD2 guiding. ASI air really makes my job easy with regards to PA and go-to functionality and hence I ahve not ventured into PC. 

Last night I was imaging the flaming star nebula and I was getting about 2 RMS total error. Most of the error was coming from RA as I had a good PA (withing 1.3 arc sec. Not sure if I need to be any lower). DEC was around 0.8 RMS. I have never got any better numbers than these frankly speaking yet my stars are nice and round. May be it is because of my widefield setup.

I did try dithering last night but had similar observations. Very long settling times (Again total RMS was about 2 arc sec). I waited about 60 s for the mount to settle down yet the RMS values were high. I also noticed that for DEC, I was doing North corrections before dither and after dithering, RA settled pretty quickly but DEC went to about 40 arc sec and was having trouble settling down. I have also seen that the auto DEC corrections don't really work and I adjust either north/south based on the corrections graph. Dithering in DEC will change the north/south correction and perhaps that's why this number goes up?

I am still very new to this so do not fully understand whats going on.

Dino,

Did you have a chance to try this again?

Captain Haddock,

Thanks for your inputs. For my Rosette nebula, I did end up not dithering at all. I have decided to take things slow and learn one thing at a time.

Thanks,
Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
Vijay <vijaysam@...>
 

I am also having the same problem with EXOS2 as well with ASI Air Pro and dithering taking too long to settle down leading to images with trails.

I increased the "Guide stability" settings to 60s, though I think I might have to increase a bit more and try. Felt with 60s, the imaging started around 40s-45s after dither and not 60s for whatever reason.
It used to be 30s and imaging used to start way earlier, so maybe 90s or even 120s could give enough time to settle on Dec and maybe improve the images preventing the trails. I will have to try it today and see how it goes.

One more observation is when calibrating for guiding, the N/S step ends up where the shift to N goes well though the return to S never comes back and hovers close to where N shifts left off, maybe a few points down and not reasonably similar to W/E shifts where it returns back to almost 0.

Thanks,
-vijay
Wes Mcdonald
 

The north south movements during dither is going to be poor due to dec backlash.  

As I have said before, I don’t think you should dither the exos2. The gain is not worth the pain. 

Wes


--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100, ESG11
ES ED 127+MoonLite Focuser, 10" LX200GPS+ MoonLite focuser+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified, ASI071 cooled OSC, ASI MM290 guide camera
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired
Devesh Pande
 

@captain haddock I was told by ES support that PA error has to be below 2 arc minutes. That's what ZWO recommends too. I don't worry about bringing it to absolute 0 as it requires very fine adjustments. Higher PA error means higher RMS on DEC.

@vijay

Same observation. The ASI air doesn't wait until 60s to start imaging. I always get trailed stars after dithering. I will try with 120 s wait time as you suggested. The amount of dither also is a big factor. For my DSLR, I set it as 10 pixels. That is more or less recommended. Not sure if  any other setting that might be tuned. Do you think DEC has to be set to auto when dithering and not north/south?

Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
Vijay <vijaysam@...>
 

I have tried DEC with auto and had trailing stars after dither. So it seems to not impact recovering of DEC after dither within a reasonable time.
I feel having the guide stability longer (maybe 120s) might introduce enough wait time which should bring back DEC to a stable rate getting images without trails.
One more thing which I noticed is the RA only option in dither settings. I presume it is more geared towards star adventurer kind of trackers which only work in RA. But with the way things behave in EXOS2, maybe its worth a try where enabling it to have the dither only happen in RA which seems to settle down quite fast before imaging preventing trails as well.
Today seems to be clear skies, will try out some of these and see how things behave with the mount.
Robert Hoskin
 

 
This is an interesting discussion!  
 
My experience is that the EXOS2 can dither ok, at least with the software I use.   Caveat: I have a very rigid DIY spreader on my tripod, so there's a mechanical difference as well as software. 
 
I'm not using an ASIair, I'm using BackYard Nikon, ASCOM, and PHD2 (multi), I spiral-dither agressively (per 3-5 lights), and I don't have a problem with trailing stars. DEC is on Auto.  Settle time is 30s.  
 
I started dithering, because I had images spoiled due to banding ("walking noise").  I decided to go with "adequate overkill" and turn the settings up aggressively.  Really haven't paid much attention to them since then, as the problem went away.  
 
The scale calculation for PHD2 is on the guiding resolution, not the imaging camera.  Out of curiosity, I went back through the PHD2 and BYN doc/posts, and worked out my movement for this post. Looks like about 30 guide-camera pixels, netting about 52 pixels on my DSLR.  I can probably dial that back a bit!  :-))
 
Anyway...grist for your mill, folks.  
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2, Serial
Scopes: SW 130P-DS, SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM 6.3, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64
BobH
 

I also read about the string and weight to "automate" the process through a meridian flip. I was putting off trying that until I finalize my cable management. In the interim, I just use a magnet as an instant on/off weight to change balance.

Your RMS errors are very similar to mine, when targeting South. However, that settle time after dithering seems really excessive - I suspect our payload weights are of the same general class, and I generally fully settle within 15-30 seconds of completing the actual dither slew - and I don't see 40" swings during that process. Something seems slightly out-of-whack.

I haven't tried off-axis guiding yet (use to do that manually 30+ years ago on my C-11), but my instincts are to do that once I add a significantly longer focal-length scope to the mix - a ways off. I don't have a feel for the practical limits of guiding with a guide scope as we are doing, so I don't have a feel if my 2"RMS is primarily the mount, or if it really reflects limitation of the setup. If I ever get around to doing that experiment, I let you know the results.

Happy imaging!

Cheers, Bob

--
Mounts: 1980's Celestron "EQ" Fork; Meade LXD55; Skywatcher Star Tracker; EXOS-II PMC-8
Optics: C-11; Meade AR5 Achromat Refractor; RedCat51; Various DSLR lenses
Cameras: ASI071 MC (DSO imaging); ASI290MM (guiding); ASI178MC (Planetary/Lunar imaging); Sony A700 DSLR
Computers: Win10Pro Laptop (ASCOM ecosystem, at-the-mount); RPi4b (INDI, on-the-scope); Win10Pro Workstation (networked remote control); Galaxy S5 Tablet
Misc: Pegasus power Pocket Adv (power mgmt, USB hub, dew/env); ZWO EAF; ZWO 1-Filter Drawer
Imaging SW: Stellarmate (low-power remote); SharpCap 4.0 Pro/Astap; PHD2; Stellarium; ASCOM 6.5.1
Processing: PixInsight; DSS; GIMP; F4W2HDU; AutoStakkert; RegiStax6
Wish-list: 5-inch class APO; Losmandy G-11; RASA-11?
BobH
 

Vijay, that sounds symptomatic of backlash - most of the "backwards" steps are being spent taking slack out of the gears, rather than moving the scope. One of the experts on this forum posted a tuning document (sorry, I don't have it at hand) that gives a very nice tutorial on how to adjust the mount when needed. Even if it came properly tuned from the factory (bit of a lottery there), eventually many of us have to make such adjustments over time as a part of long-term maintenance. While some backlash is necessary to allow the gears to turn, ideally one wants to minimize it. Some guiding software, such as PHD2, can quantify the backlash, and partially mitigate it in software - but too much can make a hash of guiding, dithering, et al.

Cheers, Bob

--
Mounts: 1980's Celestron "EQ" Fork; Meade LXD55; Skywatcher Star Tracker; EXOS-II PMC-8
Optics: C-11; Meade AR5 Achromat Refractor; RedCat51; Various DSLR lenses
Cameras: ASI071 MC (DSO imaging); ASI290MM (guiding); ASI178MC (Planetary/Lunar imaging); Sony A700 DSLR
Computers: Win10Pro Laptop (ASCOM ecosystem, at-the-mount); RPi4b (INDI, on-the-scope); Win10Pro Workstation (networked remote control); Galaxy S5 Tablet
Misc: Pegasus power Pocket Adv (power mgmt, USB hub, dew/env); ZWO EAF; ZWO 1-Filter Drawer
Imaging SW: Stellarmate (low-power remote); SharpCap 4.0 Pro/Astap; PHD2; Stellarium; ASCOM 6.5.1
Processing: PixInsight; DSS; GIMP; F4W2HDU; AutoStakkert; RegiStax6
Wish-list: 5-inch class APO; Losmandy G-11; RASA-11?
Devesh Pande
 

Well, that's strange. I have literally tried every setting in ASI air but I couldn't settle down the DEC after dither. I am unsure what am I doing wrong. I hope Vijay finds out something tonight with RA only dither.

With the 2" RMS value total, I was yesterday able to do 10 min exposures without any trailing. 

Devesh
--
EXOS 2 PMC 8
Aperture 60mm EDR
Apertura 1X field flattner
ZWO ASI Air
ZWO ASI472MC
NikonD5500a
Celestron C8
Optolong Lpro
Optolong Lextreme
Bortle 7
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