20 replies to this topic

[Zevedo]

Hi all,

For the past few days, I've been trying to set up guiding for the first time on my rig. Before all else, here is a list of my relevant equipment:

    SkyWatcher StarAdventurer GTi - Connected using GS Server
    ToupTek GPM462M
    SV Bony SV106 60mm (240mm focal length)

I have had a multitude of issues, which mainly seem to be connected to large backlash amounts. I will be attempting to fix this, but first I'd like to solve the other issue I'm having and is the subject for this thread.

So, to get straight to the point, here is how my 3 second long guiding exposures look like (please ignore the insane guiding graph, if you can):

The gain on my camera is Set to 0, and this is a 3 second exposure. Adjusting either of these, as well as screen gamma, does not seem to affect the issue at all. The mount was pointing to M42. I also noticed that this problem seems to go away if I point the mount to someplace else in the sky. For instance, here is an image with the scope pointed roughly at Polaris.

 

I also noticed this strange behavior, where throughout same length short exposures (0,2 seconds), the images would changed from clipped to less clipped. I have a video of this behavior.

 

To try and rule out a problem with the camera, I connected it to NINA as the main camera and took an exposure, which looked fine (besides the lack of focus):

Today I'm going to try to reinstall both PHD2 and Touptek Drivers and see if that helps. In the meantime I have also tried a different cable, which didn't help.

Sorry for the long thread! Hope anyone here can point me towards the right direction. Logs and video: https://drive.google...P-B?usp=sharing

 

Thanks!

Edited by Zevedo, 10 December 2024 - 11:37 AM.

[Tapio]

Yes, please share the log files.
They will help.
Set the exposure first 1 to 2 seconds first and let PHD choose the stars (it should not choose saturated stars).

PS why do you have 533mc in your profile name? Hopefully you have not chosen your imaging camera by mistake.

[Zevedo]

Yes, please share the log files.
They will help.
Set the exposure first 1 to 2 seconds first and let PHD choose the stars (it should not choose saturated stars).

PS why do you have 533mc in your profile name? Hopefully you have not chosen your imaging camera by mistake.

Here are the logs: https://drive.google...P-B?usp=sharing

 

The starts look roughly the same no matter the exposure time. Also, no, I haven't connected my imaging camera by accident, I'm using the Touptek

[Brian Carter]

First of all, if you change the y-axis to "16", your guiding will look a lot better

 

Second:  I have found limited value in putting the exposure >1s in PHD2.  Even when I can't actually see stars in the window, PHD2 can find them.  And quicker exposures lead to faster corrections, so that can't be bad?  Give it a shot, see what happens.

 

That said:  Guiding that bad usually means my PA is crazy off and I should redo it.  Check the three-star PA in NINA and see what kind of error it gives you.  After that, I would check and redo your calibration.  If the position of your guider or even rotation of the camera change a little, it won't know where to guide and your guiding goes off the rails like that really quickly.

 

After you get everything redone, there is a Tool in PHD2 called "Guiding assistant" (I think that's the name).  Let it run for five minutes and it will give you good feedback about changing PHD2 settings and an estimate of error of your alignment.

[SgrB2]

If you haven't tried it, I would suggest that you set up

the DEC side of PHD2 in the same way you have the

RA.  That is, set aggression to 70% hysteresis to 10% and

see if that eliminates the DEC oscillations.  And by all

means use Guiding assistant and implement the

parameters it suggests once you have the DEC oscillations

under control.  I assume you've balanced the telescope.

 

Cheers,

SgrB2

Edited by SgrB2, 10 December 2024 - 12:30 PM.

[happylimpet]

Hi all,

For the past few days, I've been trying to set up guiding for the first time on my rig. Before all else, here is a list of my relevant equipment:

    SkyWatcher StarAdventurer GTi - Connected using GS Server
    ToupTek GPM462M
    SV Bony SV106 60mm (240mm focal length)

I have had a multitude of issues, which mainly seem to be connected to large backlash amounts. I will be attempting to fix this, but first I'd like to solve the other issue I'm having and is the subject for this thread.

So, to get straight to the point, here is how my 3 second long guiding exposures look like (please ignore the insane guiding graph, if you can):

The gain on my camera is Set to 0, and this is a 3 second exposure. Adjusting either of these, as well as screen gamma, does not seem to affect the issue at all. The mount was pointing to M42. I also noticed that this problem seems to go away if I point the mount to someplace else in the sky. For instance, here is an image with the scope pointed roughly at Polaris.

 

I also noticed this strange behavior, where throughout same length short exposures (0,2 seconds), the images would changed from clipped to less clipped. I have a video of this behavior.

 

To try and rule out a problem with the camera, I connected it to NINA as the main camera and took an exposure, which looked fine (besides the lack of focus):

Today I'm going to try to reinstall both PHD2 and Touptek Drivers and see if that helps. In the meantime I have also tried a different cable, which didn't help.

Sorry for the long thread! Hope anyone here can point me towards the right direction. Logs and video: https://drive.google...P-B?usp=sharing

 

Thanks!

Theyre bright stars, so theyre saturating....i dont think theres anything else to say! Youve already got gain to minimum. Best not to use really short exposures as then the scope 'chases the seeing'. Best to keep them long enough to average this out...which is why people go for 3 secs. Sometimes PHD2 picks saturated stars even when told not to.

[bbasiaga]

First of all, if you change the y-axis to "16", your guiding will look a lot better

Second: I have found limited value in putting the exposure >1s in PHD2. Even when I can't actually see stars in the window, PHD2 can find them. And quicker exposures lead to faster corrections, so that can't be bad? Give it a shot, see what happens.

That said: Guiding that bad usually means my PA is crazy off and I should redo it. Check the three-star PA in NINA and see what kind of error it gives you. After that, I would check and redo your calibration. If the position of your guider or even rotation of the camera change a little, it won't know where to guide and your guiding goes off the rails like that really quickly.

After you get everything redone, there is a Tool in PHD2 called "Guiding assistant" (I think that's the name). Let it run for five minutes and it will give you good feedback about changing PHD2 settings and an estimate of error of your alignment.

Generally not recommended to go that short unless you have a SW mount that needs it. You can chase seeing, and depending on how tight your mount is and how well balanced you may find constant corrections showing good RMS, but artifacts from oscillations in the subs. In the worst case it can walk away and guiding can get really poor. Over corrected control looks like that have higher risk of unpredictable performance.


When setting gain and guide exposure, look at the SNR and the peak on the chosen star. Exposure/gain too small and the SNR will be low, and the peak value low. Shoot for about 200. If the exposure/gain is too high, that peak will have a flat at the top indicating it is saturated. Tha means it can't properly guide on that star even if it thinks it can.

Brian

[Zevedo]

First of all, if you change the y-axis to "16", your guiding will look a lot better

 

Second:  I have found limited value in putting the exposure >1s in PHD2.  Even when I can't actually see stars in the window, PHD2 can find them.  And quicker exposures lead to faster corrections, so that can't be bad?  Give it a shot, see what happens.

 

That said:  Guiding that bad usually means my PA is crazy off and I should redo it.  Check the three-star PA in NINA and see what kind of error it gives you.  After that, I would check and redo your calibration.  If the position of your guider or even rotation of the camera change a little, it won't know where to guide and your guiding goes off the rails like that really quickly.

 

After you get everything redone, there is a Tool in PHD2 called "Guiding assistant" (I think that's the name).  Let it run for five minutes and it will give you good feedback about changing PHD2 settings and an estimate of error of your alignment.

 

Hi! The reason I have it set to 3 is that it seems to be able to detect more stars than with shorter exposures. As for the PA point, I'm all set up again and got PA down to under 30'' in TPPA. After that, calibration gave me the same results. I just now ran Guiding Assistant and these were the results:

 

 

If you haven't tried it, I would suggest that you set up

the DEC side of PHD2 in the same way you have the

RA.  That is, set aggression to 70% hysteresis to 10% and

see if that eliminates the DEC oscillations.  And by all

means use Guiding assistant and implement the

parameters it suggests once you have the DEC oscillations

under control.  I assume you've balanced the telescope.

 

Cheers,

SgrB2

Where can I manually set that? I had guiding assistant suggest me the parameters and went with it. Nevermind, found the setting.

 

Theyre bright stars, so theyre saturating....i dont think theres anything else to say! Youve already got gain to minimum. Best not to use really short exposures as then the scope 'chases the seeing'. Best to keep them long enough to average this out...which is why people go for 3 secs. Sometimes PHD2 picks saturated stars even when told not to.

I'm not sure it's that simples unfortunately... It seems to be one overly saturated star, accompanied by several barely detectable ones.
 

Edited by Zevedo, 10 December 2024 - 02:14 PM.

[Tapio]

I'm all set up again and got PA down to under 30' in TPPA

 

Hope you mean arc seconds " and not arc minutes ' - 30 arc minutes is not so good...

 

Not clear so far (to me at least) what is your imaging scope.

Just hoping you haven't overloaded your mount.

[Zevedo]

Hope you mean arc seconds " and not arc minutes ' - 30 arc minutes is not so good...

 

Not clear so far (to me at least) what is your imaging scope.

Just hoping you haven't overloaded your mount.

Yes, I meant seconds.

 

It's a 533MC Pro with a Rokinon/Samyang 135mm

[Alex McConahay]

How do you select your guide star?

 

Many people just click on the best looking (brightest) star image in the frame. It is better to click on the button that tells PHD2 to choose the star. (I believe you did that, or picked a dimmer star on purpose---the crosshairs are on a rather dim star, and the secondary circles (indicating the other stars the program uses in multi-star guiding are around the brightest----which certainly must be saturating.

 

I am on the side of the people who feel you should be taking longer exposures (>1 sec). Unless your mount has really bad tracking (like some strainwave mounts do), it does not need correcting every second. 

 

Let's think for a bit about what is going wrong, and perhaps run an experiment........

 

The ugliest part of your problem is not the saturated stars, it is the oscillation between up and down in dec. 

 

Point your rig to the meridian, celestial equator, and calibrate.  

 

Then, immediately try guiding as you usually do for five minutes. Ask the display to include a trend line. Where does the trend line indicate your mount is moving over time? 

 

Now, return to the calibration point (meridian/celestial equator), and start another five minute guiding run. This time, TURN DEC GUIDING OFF. 

 

Return again to calibration point, start another five minute run, and this time, turn off dec guiding in the direction that your trend line was taking it before. (If the mount was drifting north in the run without dec guiding, turn off North in dec. ) And watch what you get. 

 

(See the manual on "Uni Directional Guiding.")

 

Now, let's assume that you do want to use uni-directional guiding..... Let's look at the aggressiveness and max motion setting. You have told PHD2 to apply ALL the correction each time it notices anything in dec.  And you have told it to apply it up to 2500 units. (You have different settings in RA on aggressiveness--Why?)_So it does.

 

If you were driving down the road, and your car started drifting to the left, you would wrench the wheel completely to the right and hold it there.  YOur car would jag to the right, where you would then jerk the wheel left and leave it there and then jerk it to the right to bring it back. But while it brings it back, it brings it too far, and you continue in this way zig-zagging across the road. Your path on the road would look like your Dec guiding graph in red. 

 

Instead, you should  turn the wheel a little to the right, gently recovering a little from the left drift. You would just move it a bit, and for only a little time. Just enough to get it moving back the other way.

 

That is not what you are doing with an aggressiveness setting of 100 (wrench it completely to the right) and a max movement of 2500 (keep the steering wheel there for a long time). 

 

As has already been said, adjust those settings a bit so you are not as aggressive in dec. And you do not apply them fully on each iteration. 

 

And, of course, check the mechanics of your mount. There is some slop somewhere. 

 

Alex

 

 

 

 

Your dec line TREND should not be moving at all.   

[Alex McConahay]

In post #11, I suggested you mess around with turning off Dec guiding, or restricting it to "north" or "south."   Then I realized that I could not remember how to do that, although I was sure it could be done. Not having access to the PHD2 program on this computer, I thought it would be good to check out how to do that. 

 

I believe it can be done on the main screen-----where your screen says "auto."  I think pulling that down let's you choose between something like North/South/Auto.

 

If I am wrong on that, you can access it in the brain/Advanced Setup/Algorithms. 

 

The text from the instructions says 

 

The default value of 'auto' tells PHD2 that some reversals in direction are acceptable, subject to the behavior of the various guiding algorithms.  However, if your mount has severe declination backlash, you may want to prevent direction reversal altogether. You could then select either 'north' or 'south' to restrict corrections to only that direction (uni-directional Dec guiding).  Keep in mind, however, that an over-shoot in correction with one of these modes might leave the star positioned off-target for an extended period of time. So you'll probably want to use conservative aggressiveness values for either 'North' or 'South' modes and you may want to intentionally degrade the polar alignment to help keep the drift rate larger than the deflections caused by seeing.  Finally, a choice of 'off'' here disables declination guiding altogether, an appropriate choice for simple tracking mounts that don't support Dec guiding. 

 

Alex

Attached Thumbnails

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[archiebald]

First of all, if you change the y-axis to "16", your guiding will look a lot better

 

Second:  I have found limited value in putting the exposure >1s in PHD2.  Even when I can't actually see stars in the window, PHD2 can find them.  And quicker exposures lead to faster corrections, so that can't be bad?  Give it a shot, see what happens.

 

That said:  Guiding that bad usually means my PA is crazy off and I should redo it.  Check the three-star PA in NINA and see what kind of error it gives you.  After that, I would check and redo your calibration.  If the position of your guider or even rotation of the camera change a little, it won't know where to guide and your guiding goes off the rails like that really quickly.

 

After you get everything redone, there is a Tool in PHD2 called "Guiding assistant" (I think that's the name).  Let it run for five minutes and it will give you good feedback about changing PHD2 settings and an estimate of error of your alignment.

Wouldn't the shorter exposure times make you susceptible to chasing the seeing?

 

More than a few times when my guiding was erratic, I was able to improve it just by exposing longer and averaging out the scintillation. (not every time, but numerous enough not to be a coincidence)

[Andros246]

How can an am5 under the same sky as any ordinary mount not chase the seeing but the traditional mount will.

Never made any logical sense it shouldn’t have anything to do with the seeing.

I run 1 second with a gem28 my periodic error is about the same as a harmonic drive and just as “rapid”

Edited by Andros246, 10 December 2024 - 11:18 PM.

[Alex McConahay]

I do not understand "chasing the seeing." There is no way that guiding (with our equipment) can compensate for seeing. Positional changes (of a guide star) caused by "seeing" happen ten to hundreds of times per second. You cannot keep up with them if you are cycling the image/analyze/correct at significantly less than that rate (ten to hundreds of times per second).  By the time you have adjusted your rig, the seeing has moved the star ten to thousands of times. But few of those movements have been at all large. 

 

What seeing can do is make the star look bigger over time than it should. One split second the center of the star will be in position x,y. The next in position x1y1, and then the next split second in x2y2. And it just goes on and on. When you add up all those random hits over the time of the exposure, the light is spread over a larger area than it might be if seeing were not an issue. This makes the star bigger, but does not change the overall position of the collection of hits that define the star (much). 

 

We could not chase seeing with our rigs even if we wanted to. 

 

What guiding can help with is the less frequent change in star positions. These include flexures, irregular teeth in the gears, polar alignment, and other things that happen over seconds or more in most mounts. 

 

The general advice is that we have two to four second exposures. 

 

Why is a strain wave mount instead usually handled with very short exposures? Because the nature of the mount drive has more irregularities in the drive train than well-made traditional mounts. To correct for these movement errors, people have found it better to guide with shorter cycles. Again, chasing seeing is not the issue. You just don't have to wait as long with these mounts to have tracking errors show! (I believe that is what I have been told.)

 

Check out what PHD2 people (Bruce Waddington) says about this issue in the appendix (page 15 etc.) here......https://openphdguidi..._Guide_Logs.pdf

 

Alex

Edited by Alex McConahay, 11 December 2024 - 12:36 AM.

[archiebald]

I do not understand "chasing the seeing." There is no way that guiding (with our equipment) can compensate for seeing. Positional changes (of a guide star) caused by "seeing" happen ten to hundreds of times per second. You cannot keep up with them if you are cycling the image/analyze/correct at significantly less than that rate (ten to hundreds of times per second).  By the time you have adjusted your rig, the seeing has moved the star ten to thousands of times. But few of those movements have been at all large. 

 

What seeing can do is make the star look bigger over time than it should. One split second the center of the star will be in position x,y. The next in position x1y1, and then the next split second in x2y2. And it just goes on and on. When you add up all those random hits over the time of the exposure, the light is spread over a larger area than it might be if seeing were not an issue. This makes the star bigger, but does not change the overall position of the collection of hits that define the star (much). 

 

We could not chase seeing with our rigs even if we wanted to. 

 

What guiding can help with is the less frequent change in star positions. These include flexures, irregular teeth in the gears, polar alignment, and other things that happen over seconds or more in most mounts. 

 

The general advice is that we have two to four second exposures. 

 

Why is a strain wave mount instead usually handled with very short exposures? Because the nature of the mount drive has more irregularities in the drive train than well-made traditional mounts. To correct for these movement errors, people have found it better to guide with shorter cycles. Again, chasing seeing is not the issue. You just don't have to wait as long with these mounts to have tracking errors show! (I believe that is what I have been told.)

 

Check out what PHD2 people (Bruce Waddington) says about this issue in the appendix (page 15 etc.) here......https://openphdguidi..._Guide_Logs.pdf

 

Alex

Just to be clear, the question about strain wave usage came from someone else.  The OP was not referring to a strain wave mount, and I don't use one either.

 

Not to be argumentative, but if I read page 10 of that document you've linked to, "chasing the seeing" is described in relation to over correction during guiding and seemingly contradicts what you have stated.  I'd read that document a couple of years ago when I started AP and it's where my original understanding came from; 

 

"A common cause for this in RA is using a min-move setting that is too small for that night’s seeing conditions or an exposure time that is too short (e.g. 1 sec)"

 

Granted this was written 8-9 years ago, and technology and thinking may have changed but those are the words of Bruce Waddington.

 

If I think in terms of industrial control which I'm more familiar with, the term "chasing the seeing" could be replaced with "hunting".  Even though the differences in star centroid position you describe are small, they are a disturbance in the feedback loop.  Again, just thinking in terms of industrial control, averaging those differences out as much as possible (longer exposure) should have the effect of minimizing the disturbance.  (and of course I realize there are many other elements mixed in there too)

 

A similar assessment is made on pages 16-17 of the document from Bruce.

Edited by archiebald, 11 December 2024 - 02:49 AM.

[TheXtra10th]

First of all, if you change the y-axis to "16", your guiding will look a lot better

 

Second:  I have found limited value in putting the exposure >1s in PHD2.  Even when I can't actually see stars in the window, PHD2 can find them.  And quicker exposures lead to faster corrections, so that can't be bad?  Give it a shot, see what happens.

 

That said:  Guiding that bad usually means my PA is crazy off and I should redo it.  Check the three-star PA in NINA and see what kind of error it gives you.  After that, I would check and redo your calibration.  If the position of your guider or even rotation of the camera change a little, it won't know where to guide and your guiding goes off the rails like that really quickly.

 

After you get everything redone, there is a Tool in PHD2 called "Guiding assistant" (I think that's the name).  Let it run for five minutes and it will give you good feedback about changing PHD2 settings and an estimate of error of your alignment.

The exposure time is dependent upon the seeing conditions…..  if you have excellent seeing conditions, then 1 sec or less exposure will work, however if you have avg or below avg seeing, then short exposures can create problems with over correction and “chasing” the seeing, my personally, I use mostly 3 sec exposures for guiding as I rarely have excellent seeing conditions 

[Zevedo]

How do you select your guide star?

 

Many people just click on the best looking (brightest) star image in the frame. It is better to click on the button that tells PHD2 to choose the star. (I believe you did that, or picked a dimmer star on purpose---the crosshairs are on a rather dim star, and the secondary circles (indicating the other stars the program uses in multi-star guiding are around the brightest----which certainly must be saturating.

 

I am on the side of the people who feel you should be taking longer exposures (>1 sec). Unless your mount has really bad tracking (like some strainwave mounts do), it does not need correcting every second. 

 

Let's think for a bit about what is going wrong, and perhaps run an experiment........

 

The ugliest part of your problem is not the saturated stars, it is the oscillation between up and down in dec. 

 

Point your rig to the meridian, celestial equator, and calibrate.  

 

Then, immediately try guiding as you usually do for five minutes. Ask the display to include a trend line. Where does the trend line indicate your mount is moving over time? 

 

Now, return to the calibration point (meridian/celestial equator), and start another five minute guiding run. This time, TURN DEC GUIDING OFF. 

 

Return again to calibration point, start another five minute run, and this time, turn off dec guiding in the direction that your trend line was taking it before. (If the mount was drifting north in the run without dec guiding, turn off North in dec. ) And watch what you get. 

 

(See the manual on "Uni Directional Guiding.")

 

Now, let's assume that you do want to use uni-directional guiding..... Let's look at the aggressiveness and max motion setting. You have told PHD2 to apply ALL the correction each time it notices anything in dec.  And you have told it to apply it up to 2500 units. (You have different settings in RA on aggressiveness--Why?)_So it does.

 

If you were driving down the road, and your car started drifting to the left, you would wrench the wheel completely to the right and hold it there.  YOur car would jag to the right, where you would then jerk the wheel left and leave it there and then jerk it to the right to bring it back. But while it brings it back, it brings it too far, and you continue in this way zig-zagging across the road. Your path on the road would look like your Dec guiding graph in red. 

 

Instead, you should  turn the wheel a little to the right, gently recovering a little from the left drift. You would just move it a bit, and for only a little time. Just enough to get it moving back the other way.

 

That is not what you are doing with an aggressiveness setting of 100 (wrench it completely to the right) and a max movement of 2500 (keep the steering wheel there for a long time). 

 

As has already been said, adjust those settings a bit so you are not as aggressive in dec. And you do not apply them fully on each iteration. 

 

And, of course, check the mechanics of your mount. There is some slop somewhere. 

 

Alex

 

 

 

 

Your dec line TREND should not be moving at all.   

Hi Alex

Thank you so much for your insight, your steering analogy made a lot of sense and really helped me to understand what each of those different settings meant. Though I didn't have time to run all of the tests you mentioned, I did activate the trendlines. I found them to be pretty stable around the middle of the graph, which I suppose means the mount isn't drifting in any direction?

 

I then lowered the aggressiveness to 70% and later to 60%, which at first seemed to help out a ton. This is what my graph looked like during a 5 minute exposure with aggressiveness at 70% and max pulse duration at 2400. It held it together like that for quite a while, until I decided to slew to my target for the night (M42). As soon as I did that, it all went haywire again. The total error shot up to 8, my stars became clipped again (this was fixed by changing the exposure time to 2sec and back to 3sec again). A warning popped up mentioning the meridian flip, suggesting I checked if the "Reverse Dec output after meridian flip" was wrong. Since It was disabled, I enabled it to see if it helped. After it calibrated itself again, guiding ensued, but with a total error above 1px.

 

I also enabled the backlash compensation setting, which didn't seem to help (I didn't change any of the values however, so it may have been poorly adjusted to my case)

 

At this point I am leaning towards the possibility that there is something mechanically wrong with the mount, though I tightened RA yesterday. I'll have to wait for more clear nights to do some more testing, but for now I guess I'll study up on guiding.

[Alex McConahay]

>>>>>At this point I am leaning towards the possibility that there is something mechanically wrong with the mount, though I tightened RA yesterday.

 

Yup, check how much play you have in the dec gears. 

Alex

[Alex McConahay]

>>>>>>Not to be argumentative, but if I read page 10 of that document you've linked to, "chasing the seeing" is described in relation to over correction during guiding and seemingly contradicts what you have stated. 

 

Actually, what you have stated and what I have stated is pretty much the same overall.......Unless you have a mount that does not track well then short exposures are not really all that productive. 

 

My statements that:

I do not understand "chasing the seeing." and 

We could not chase seeing with our rigs even if we wanted to.

 

Those are just ways of saying that, in my mind, "seeing happens so fast that it is silly to try to keep up with it." And anybody adjusting the exposure time downwards is deluding himself or herself. You simply cannot catch seeing. So, it makes no sense to chase it.

 

   

  

 

>>>>>>>>Granted this was written 8-9 years ago, and technology and thinking may have changed but those are the words of Bruce Waddington.

 

I do not think the technology related to guiding has actually changed much. And the overall concepts still seem to apply. 

 

 

>>>>>>>>>  Again, just thinking in terms of industrial control, averaging those differences out as much as reasonable (longer exposure) should have the effect of minimizing the disturbance.  (and of course I realize there are many other elements mixed in there too)

 

Yes, note how Waddington separates the fast (short frequency and un-chase-able in my mind) movements due to seeing from the longer frequency changes due to polar misalignment, mount errors, periodic errors, tube sag, mirror shift, and all that--the relatively non-random things one can reasonably correct for.

 

>>>>>>>>>A similar assessment is made on pages 16-17 of the document from Bruce.

 

Yeah, I got a whole lot more from that part of the appendix than the earlier part. 

 

ALex

[bbasiaga]

How can an am5 under the same sky as any ordinary mount not chase the seeing but the traditional mount will.

Never made any logical sense it shouldn’t have anything to do with the seeing.

I run 1 second with a gem28 my periodic error is about the same as a harmonic drive and just as “rapid”

The tracking error of the SW mounts is often greater than the effects of seeing over the course of that 1s, and is non-periodic.  Whereas a GEM or other worm gear mount typically have slower evolving and periodic (predictable) errors which means short term movements (1-2s or less) are attributable to seeing.   

 

Brian