RAPAS on Mach2


Terri Zittritsch
 

Hi all,
I've received a RAPAS to use with my Mach2 when I'm doing outreach or in other instances when I don't use a computer.   But I've not been very satisfied with the results from the polemaster I have, once I get down to actually measuring drift.. The actual drift implies much less accuracy than advertised, or that many claim to achieve.  I have not been able to get close to 30 arc seconds, but you wouldn't think this from the screen indication.   Given others experiences I've read about, I am also hopeful the RAPAS will do better, but I'm a bit unclear on this point.

So now I have the RAPAS, for a Mach2.  It is attached on the side of the mount, rather than through the central axis as we know the Mach2 doesn't have this capability.    I've also read that the mount needs to be leveled east-west accurately because the RAPAS needs to be vertical (it is fixed, not rotating in any installation).    But there is only so much accuracy in leveling the mount, or more importantly, getting repeatability.   A bubble level or electronic level is only so accurate.   I've read that .5mm of tripod settling on one foot with 1M separation between the feet will result in adding 2 arc minutes of alignment error.     I don't know how Chris Woodhouse calculated this, and maybe I'll draw this up as a geometry exercise, but you get my drift (pun totally intended).   Leveling by-leg is likely millimeters of inaccuracy or non-repeatability use to use.   0.5mm is totally unrealistic.  

I think the scope load moving side to side may introduce at least a .5mm if not more, or settling.    I'm reading in the RAPAS instructions I received, which implies that accuracy is effected by loading (so may not be repeatable scope-scope unless they have the same weight profile).

So I'm wondering if I'm chasing something that isn't achievable.. like chasing the seeing.   Am I chasing after good polar alignment that just isn't achievable on a portable setup without doing drift alignment?     For instance, for unguided imaging.   

What is the practical accuracy, and repeatability of the RAPAS?  Has anyone here actually checked it on a portable installation.   I've asked Roland and he said he doesn't know, but that I should ask those on the forum.


Terri



  









Roland Christen
 

No need to level the mount super accurately. The polar scope will still work well even if you are off by many degrees.

If your mount is not vertical, you can align the polar scope reticle to be vertical:
1) Aim the mount so that the scope points directly at Polaris (put Polaris on the center crosshair).
2) using the mount's altitude adjuster, run Polaris up and down the vertical crosshair. Loosen and turn the eyepiece until the crosshair is aligned with the up-down motion of Polaris.
3) tighten the eyepiece in place and then use the alt and az adjusters to put Polaris at the proper place on the reticle according to the polar app.

Rolando



-----Original Message-----
From: Terri Zittritsch <theresamarie11@...>
To: main <main@ap-gto.groups.io>
Sent: Thu, Apr 16, 2020 9:59 am
Subject: [ap-gto] RAPAS on Mach2

Hi all,
I've received a RAPAS to use with my Mach2 when I'm doing outreach or in other instances when I don't use a computer.   But I've not been very satisfied with the results from the polemaster I have, once I get down to actually measuring drift.. The actual drift implies much less accuracy than advertised, or that many claim to achieve.  I have not been able to get close to 30 arc seconds, but you wouldn't think this from the screen indication.   Given others experiences I've read about, I am also hopeful the RAPAS will do better, but I'm a bit unclear on this point.

So now I have the RAPAS, for a Mach2.  It is attached on the side of the mount, rather than through the central axis as we know the Mach2 doesn't have this capability.    I've also read that the mount needs to be leveled east-west accurately because the RAPAS needs to be vertical (it is fixed, not rotating in any installation).    But there is only so much accuracy in leveling the mount, or more importantly, getting repeatability.   A bubble level or electronic level is only so accurate.   I've read that .5mm of tripod settling on one foot with 1M separation between the feet will result in adding 2 arc minutes of alignment error.     I don't know how Chris Woodhouse calculated this, and maybe I'll draw this up as a geometry exercise, but you get my drift (pun totally intended).   Leveling by-leg is likely millimeters of inaccuracy or non-repeatability use to use.   0.5mm is totally unrealistic.  

I think the scope load moving side to side may introduce at least a .5mm if not more, or settling.    I'm reading in the RAPAS instructions I received, which implies that accuracy is effected by loading (so may not be repeatable scope-scope unless they have the same weight profile).

So I'm wondering if I'm chasing something that isn't achievable.. like chasing the seeing.   Am I chasing after good polar alignment that just isn't achievable on a portable setup without doing drift alignment?     For instance, for unguided imaging.   

What is the practical accuracy, and repeatability of the RAPAS?  Has anyone here actually checked it on a portable installation.   I've asked Roland and he said he doesn't know, but that I should ask those on the forum.


Terri



  









Terri Zittritsch
 

On Thu, Apr 16, 2020 at 11:17 AM, uncarollo2 <chris1011@...> wrote:
No need to level the mount super accurately. The polar scope will still work well even if you are off by many degrees.
 
If your mount is not vertical, you can align the polar scope reticle to be vertical:
1) Aim the mount so that the scope points directly at Polaris (put Polaris on the center crosshair).
2) using the mount's altitude adjuster, run Polaris up and down the vertical crosshair. Loosen and turn the eyepiece until the crosshair is aligned with the up-down motion of Polaris.
3) tighten the eyepiece in place and then use the alt and az adjusters to put Polaris at the proper place on the reticle according to the polar app.
 
Rolando
Roland, I didn't expect you to respond.    The RAPAS feels like the rest of the kit I have from AP, solid and built like a tank!  Being an engineer, I can appreciate it all.

Throughout the instructions I received, in numerous places, are notes to make sure the mount is level which is why I asked.  It didn't take long to think about the implications of the mount not being level, or more accurately, the RAPAS not being precisely vertical, on the accuracy on polar alignment.   The instructions note that you can loosen the 'do not loosen' screws to readjust the reticle if it's moved during shipping, but doesn't seem to be part of the normal (do every time) alignment process.   At least not in the instructions I have, so thanks for sharing this.
I'm just trying to understand whether there is any way to do really accurate polar alignment, 30" or less,  in order to do short unguided exposures, without going to the traditional drift alignment.. I've found drift alignment to be a miserable process to go through.  Life is too short, and clear skies much shorter!   I'm not setting up on a level surface, or on a pier, every night is different.   Since I have all of the equipment, guiding is not a terrible thing to have to do.   I'm just thinking I have this really really nice mount, and is there any way to take advantage of it's full capability in a portable situation.   


Terri




W Hilmo
 

I have found the RAPAS to be quite accurate.

 

It is suggested to have the mount level because if it’s not level in the east/west direction, it means that the reticule would be rotated clockwise or counter-clockwise, depending on which direction the mount is unlevel.  If you stop and think about it, you would need to have a significant unlevel situation for it to be a problem.  Certainly if the mount “looks” level, then it should be fine.

 

When I set up in the field, my general workflow is to set up the mount during the day and go through the daytime polar alignment routine.  Then, at dusk I use the RAPAS to do a final tweak to the polar alignment.  If I do this, and then blink a stack of a whole night’s imaging, there is no noticeable field rotation between the first and last images of the session.  The daytime alignment takes me two to three minutes while the sun is up, and the tweak with the RAPAS takes about 30 seconds.

 

If you are going to image unguided, my suggestion is to do an APPM run before it gets dark enough that you are wasting productive imaging time, so that you can use a tracking model.  You should be easily able to get a 100 point, or so, run before it gets really dark.  The tracking model will compensate for any residual polar alignment error (which, from my experience with the RAPAS, will be really small, if noticeable at all).

 

I did do one really good PEMPro polar alignment to check the RAPAS calibration.  This is a one time exercise per mount (I have two mounts, so I’ve done it once for each).  To be honest, though, I found that just as shipped (without the one-time calibration), the accuracy of the RAPAS is pretty good.

 

 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 10:28 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

On Thu, Apr 16, 2020 at 11:17 AM, uncarollo2 <chris1011@...> wrote:

No need to level the mount super accurately. The polar scope will still work well even if you are off by many degrees.

 

If your mount is not vertical, you can align the polar scope reticle to be vertical:

1) Aim the mount so that the scope points directly at Polaris (put Polaris on the center crosshair).

2) using the mount's altitude adjuster, run Polaris up and down the vertical crosshair. Loosen and turn the eyepiece until the crosshair is aligned with the up-down motion of Polaris.

3) tighten the eyepiece in place and then use the alt and az adjusters to put Polaris at the proper place on the reticle according to the polar app.

 

Rolando

Roland, I didn't expect you to respond.    The RAPAS feels like the rest of the kit I have from AP, solid and built like a tank!  Being an engineer, I can appreciate it all.

Throughout the instructions I received, in numerous places, are notes to make sure the mount is level which is why I asked.  It didn't take long to think about the implications of the mount not being level, or more accurately, the RAPAS not being precisely vertical, on the accuracy on polar alignment.   The instructions note that you can loosen the 'do not loosen' screws to readjust the reticle if it's moved during shipping, but doesn't seem to be part of the normal (do every time) alignment process.   At least not in the instructions I have, so thanks for sharing this.
I'm just trying to understand whether there is any way to do really accurate polar alignment, 30" or less,  in order to do short unguided exposures, without going to the traditional drift alignment.. I've found drift alignment to be a miserable process to go through.  Life is too short, and clear skies much shorter!   I'm not setting up on a level surface, or on a pier, every night is different.   Since I have all of the equipment, guiding is not a terrible thing to have to do.   I'm just thinking I have this really really nice mount, and is there any way to take advantage of it's full capability in a portable situation.   


Terri



Roland Christen
 


The instructions note that you can loosen the 'do not loosen' screws to readjust the reticle if it's moved during shipping,
You can never adjust the reticle, it is permanently affixed inside the eyepiece. However the eyepiece is simply held in the back of the polar scope via a small setscrew, and this entire assembly can be rotated. We made this so you can do fine adjustment of the vertical reticle line in the field. Even if you are off several degrees it has very little if any effect on the actual polar alignment.

Rolando


-----Original Message-----
From: Terri Zittritsch <theresamarie11@...>
To: main <main@ap-gto.groups.io>
Sent: Thu, Apr 16, 2020 12:27 pm
Subject: Re: [ap-gto] RAPAS on Mach2

On Thu, Apr 16, 2020 at 11:17 AM, uncarollo2 <chris1011@...> wrote:
No need to level the mount super accurately. The polar scope will still work well even if you are off by many degrees.
 
If your mount is not vertical, you can align the polar scope reticle to be vertical:
1) Aim the mount so that the scope points directly at Polaris (put Polaris on the center crosshair).
2) using the mount's altitude adjuster, run Polaris up and down the vertical crosshair. Loosen and turn the eyepiece until the crosshair is aligned with the up-down motion of Polaris.
3) tighten the eyepiece in place and then use the alt and az adjusters to put Polaris at the proper place on the reticle according to the polar app.
 
Rolando
Roland, I didn't expect you to respond.    The RAPAS feels like the rest of the kit I have from AP, solid and built like a tank!  Being an engineer, I can appreciate it all.

Throughout the instructions I received, in numerous places, are notes to make sure the mount is level which is why I asked.  It didn't take long to think about the implications of the mount not being level, or more accurately, the RAPAS not being precisely vertical, on the accuracy on polar alignment.   The instructions note that you can loosen the 'do not loosen' screws to readjust the reticle if it's moved during shipping, but doesn't seem to be part of the normal (do every time) alignment process.   At least not in the instructions I have, so thanks for sharing this.
I'm just trying to understand whether there is any way to do really accurate polar alignment, 30" or less,  in order to do short unguided exposures, without going to the traditional drift alignment.. I've found drift alignment to be a miserable process to go through.  Life is too short, and clear skies much shorter!   I'm not setting up on a level surface, or on a pier, every night is different.   Since I have all of the equipment, guiding is not a terrible thing to have to do.   I'm just thinking I have this really really nice mount, and is there any way to take advantage of it's full capability in a portable situation.   


Terri




Terri Zittritsch
 

On Thu, Apr 16, 2020 at 01:47 PM, W Hilmo wrote:

 

When I set up in the field, my general workflow is to set up the mount during the day and go through the daytime polar alignment routine.  Then, at dusk I use the RAPAS to do a final tweak to the polar alignment.  If I do this, and then blink a stack of a whole night’s imaging, there is no noticeable field rotation between the first and last images of the session.  The daytime alignment takes me two to three minutes while the sun is up, and the tweak with the RAPAS takes about 30 seconds.

 

Thanks W Hilmo,

Not sure I ever see field rotation with any of my gross polar alignment methods.  I think you'd have to be pretty far off to see field rotation (but honestly don't know what that would be).  I'm trying to understand what kind of measured repeatable polar alignment people get.    Is 2 minutes, 3 minutes?   30 seconds?   With Polemaster, it's advertised at 30", and I see all kinds of claims on-line (hard to believe claims.. and claims that would be hard to even measure), but who knows.  Maybe I am just the worst polar aligner ever.    If I can do an accurate polar alignment (30") in 30 seconds, I will be exceptionally happy!!   I've never tried the daytime polar alignment.


Terri



W Hilmo
 

Honestly, I’ve never measured my polar alignment error.

 

Beyond that, I don’t even know how to measure it in a way that would be useful in conversation.  I don’t know if you follow Cloudy Nights or not, but there is a near obsession over there with polar alignment.  I’ve seen people making polar alignment error claims that border on the ridiculous (like people claiming to be within 5” of the pole, etc.)  The drift from a 5” polar alignment error would be so small that I don’t know how you could detect it with a single exposure.  I would think that looking at the total field rotation for an entire night would be a better way to try and see a very small error.  I am pretty sure that people are just running some tool like a PoleMaster or SharpCap and just repeating what the software claims.  The thing is, that the software claims are not repeatable, even in the same session.  It’s made even more confusing because I am pretty sure that different software packages calculate the polar alignment error differently.

 

Even with PEMPro, which is the gold standard for software aided drift alignments, I can watch the calculated error bounce around by some number of arc seconds with each exposure, just due to seeing effects.

 

I take a more pragmatic view.  If I don’t get any noticeable drift in a single sub, and if I don’t get any field rotation over a night of imaging the same object, then I’ll call the polar alignment “good enough”.  If your goal is to do longish exposures unguided, especially at a longer focal length, then I would probably do it one of two ways:  If you take the time to run APCC, an APPM model will compensate for any polar misalignment, as well as drift from other factors (as long as they are repeatable).  That would be my preferred method.  If I didn’t want to do an APPM run for some reason, then I would do the RA Drift Alignment that’s described on the Astro-Physics site at the below link.  To do it, I would run PHD2 with my main imaging camera and guide corrections disabled.  This would give me a graph of the guide star during tracking that I could use to know which corrections to make:

 

https://astro-physics.info/tech_support/mounts/drift-alignment-ra-correction-method.pdf

 

The other option, that is new to the keypad firmware that will be available for the Mach2, will be that you can get tracking compensation right from the keypad (and it will also be available for the CP4).  I don’t believe that any of us have that keypad firmware yet, so I don’t know of anyone outside of the Astro-Physics folks that have first hand experience with it.  If I understand what I’ve heard correctly, it will work by calibrating on a couple of stars in the path of your object and building custom tracking rates for your specific target.  I’m guessing that it will be pretty effective.

 

At the end of the day, I believe that it’s important to understand a few methods to do an  effective polar alignment and also to not obsess over it.

 

In the meantime, how do you know that your polar alignment is causing problematic drift?  If the Mach2 ships with PEMPro, I would suggest that you start its polar alignment wizard and let it track for a while.  It will clearly show you any drift (and offer the change to make an adjustment to correct it).  If you don’t have PEMPro, then you can do a similar thing with PHD2 (as I described above, using it to facilitate a drift alignment).

 

And finally, I want to close the loop on a comment that I made earlier about my personal workflow at field sites.  I mentioned that I do both a daytime polar alignment and also use the RAPAS to tweak it.  The purpose of the daytime polar alignment is to get the mount reasonably close to polar aligned before it starts to get dark.  That way, when it gets to be dusk, you are pretty much guaranteed that Polaris will be both inside the view of the RAPAS and also obvious.  If you wait until after dark and start with the RAPAS, it can be tricky to find Polaris correct, especially if it lands outside of the RAPAS field of view.  In that case, it takes longer than 30 seconds (and I’ve seen more than one person polar align to Kochab in that scenario).

 

Hope that you find this information useful,

-Wade

 

 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 12:30 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

Thanks W Hilmo,

Not sure I ever see field rotation with any of my gross polar alignment methods.  I think you'd have to be pretty far off to see field rotation (but honestly don't know what that would be).  I'm trying to understand what kind of measured repeatable polar alignment people get.    Is 2 minutes, 3 minutes?   30 seconds?   With Polemaster, it's advertised at 30", and I see all kinds of claims on-line (hard to believe claims.. and claims that would be hard to even measure), but who knows.  Maybe I am just the worst polar aligner ever.    If I can do an accurate polar alignment (30") in 30 seconds, I will be exceptionally happy!!   I've never tried the daytime polar alignment.


Terri


Dean Jacobsen
 

On Thu, Apr 16, 2020 at 01:15 PM, W Hilmo wrote:
and I’ve seen more than one person polar align to Kochab in that scenario).
I didn’t know anyone was watching me...  🙂

I used just the RAPAS for aligning my portable imaging rig for years.  I have no idea how close it was or how repeatable it was from session to session.  It is a great time saver.
 
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Terri Zittritsch
 

Hi Wade, peace..  just trying to understand.    Like I said in my original post, it may be that I'm just seeking something that isn't really practical or possible.   I have a full guiding setup, but when I get these posts using encoder mounts or my mount, showing incredibly flat controlled tracking, I'm trying to see if I can achieve this as well.     

I see the same things in forums, on claims of incredibly precise polar alignment, and as I said in the previous post, I don't know how they can make such claims.  I spent an hour one night polar drift alignment and had better alignment than usual, but it took an hour, and it still wasn't good enough for very long subs.   Long subs for me, with a CMOS camera, are still under 10 minutes or less.  I've done 20 minutes, but it's unusual.   Most of my subs are 1 minute (luminosity).    Although, having purchased some chroma 3nm filters, those seem to take some really long exposures to get a good amount of signal!

I measure drift in PHD2, using their drift alignment tool.. which takes forever to settle.. so it's a long process (for me).   Usually when I'm doing  polar alignment, I'm set up with camera, filter wheel, etc.. and want to do something that doesn't require me to take it apart and put in an eyepiece.    And PHD2 also gives me an estimate of my polar alignment error, which is based on drift, not instantaneous bouncing around the mean which I understand is all atmosphere.

I've only done one model, a 35 point small model, and I think it took around 25 minutes (it's been a while since clear skies).    And most of the plate solves were pretty fast.    I noticed the meridian points, solved twice, and most others once, so it does more than 35 solves for 35 points.    I use SGPro, which seems a bit slow to download files from my camera, which may make it slower than others.    The results of the 35 point model did not allow 1 minute subs, and I had unacceptably elongated stars.      But that's one data point,  and there is a lot to learn.  


Terri



W Hilmo
 

“Hi Wade, peace..  just trying to understand.”

 

No problem.  Likewise, I’m just trying to offer some suggestions.

 

I tend to be overly verbose when I write, which probably overcomplicates things.  It probably wasn’t clear, but I’ve ever even used an eyepiece with my two main imaging scopes.  Everything that I’ve suggested is intended to be “imaging rig friendly” and fairly simple to do.

 

Regarding your previous attempts to image unguided, what kind of scope are you using?  I do most of my imaging with an EdgeHD 8, and I simply cannot do unguided imaging with it with any kind of regularity.  The issue is that the primary mirror just has too much movement, even with the focus clutches locked.  There is obvious star trailing after 3 minutes, and 5 minute subs are completely unusable to me.  I have to use an OAG.  An APPM model doesn’t really help a lot with this because the mirror movement seems to be non-repeatable.

 

When you do an APPM run, how much of the time is spent waiting for the image to download?  I was using a CMOS camera with USB 3 downloads for a while, and it would download a 1x1 frame in just a couple of seconds.  My current camera is a CCD with USB 2, and it takes a *long* time to download a 1x1 frame.  To mitigate this, I do 5 second exposures with 2x2 binning whenever I plate solve (either inside of SGP or with APPM).  That speeds things up considerably.  I spend less than an hour to get 100-150 points.  I suspect that your DSLR can probably download a lower resolution as well.  The last time that I binned a DSLR was many years ago with a Canon 20D, and it lost the Bayer matrix information when binned 2x2, but that was no big deal for plate solving.

 

My personal opinion that is unguided imaging is not something that interests me much.  It takes me about an hour to really dial in a new guider (what with focusing through my OAG and such), but once I’ve done that, it’s all automatic.  Since I always set up with the camera, OAG and guider at the same orientation, I don’t even need to recalibrate the guide software after setting up.

 

-Wade

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 1:57 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

Hi Wade, peace..  just trying to understand.    Like I said in my original post, it may be that I'm just seeking something that isn't really practical or possible.   I have a full guiding setup, but when I get these posts using encoder mounts or my mount, showing incredibly flat controlled tracking, I'm trying to see if I can achieve this as well.     

I see the same things in forums, on claims of incredibly precise polar alignment, and as I said in the previous post, I don't know how they can make such claims.  I spent an hour one night polar drift alignment and had better alignment than usual, but it took an hour, and it still wasn't good enough for very long subs.   Long subs for me, with a CMOS camera, are still under 10 minutes or less.  I've done 20 minutes, but it's unusual.   Most of my subs are 1 minute (luminosity).    Although, having purchased some chroma 3nm filters, those seem to take some really long exposures to get a good amount of signal!

I measure drift in PHD2, using their drift alignment tool.. which takes forever to settle.. so it's a long process (for me).   Usually when I'm doing  polar alignment, I'm set up with camera, filter wheel, etc.. and want to do something that doesn't require me to take it apart and put in an eyepiece.    And PHD2 also gives me an estimate of my polar alignment error, which is based on drift, not instantaneous bouncing around the mean which I understand is all atmosphere.

I've only done one model, a 35 point small model, and I think it took around 25 minutes (it's been a while since clear skies).    And most of the plate solves were pretty fast.    I noticed the meridian points, solved twice, and most others once, so it does more than 35 solves for 35 points.    I use SGPro, which seems a bit slow to download files from my camera, which may make it slower than others.    The results of the 35 point model did not allow 1 minute subs, and I had unacceptably elongated stars.      But that's one data point,  and there is a lot to learn.  


Terri


Roland Christen
 

Hi All,

Just want to throw this trick into the mix. I've posted this before in more detail, but I'll keep it very simple. If you don't want to use a polar scope:

After basic polar alignment (any basic method that gets you close) I send the scope to a star at or very near the zenith and take an image. It won't be in the center, but hopefully somewhere in the frame. I put the exposure on "continuous" and center the star, followed by a recal. This is my overhead reference star for the next step.

Step 2, I slew to a star in the south near the meridian line and on the same side of the meridian. I then use the Azimuth adjuster to bring that star to the centerline in the RA direction. Dec may have an error, but ignore that. That's it, you're done with the Azimuth axis. Takes about 2 minutes.

Now all you have left is the Altitude axis. That adjustment can be done by doing a meridian delay and slewing to that same star in the south on the opposite side. Now bring the star 1/2 way to the centerline using the altitude axis. RA may have an error but ignore that. That's it, you are polar aligned. Takes maybe another 2 - 3 minutes.

I might then watch the overhead star drift and maybe tweak the alignment, usually requires very tiny amount of adjustment if any. Usually good enough for 5 minute exposures with an 800mm focal length.

Rolando



-----Original Message-----
From: W Hilmo <y.groups@...>
To: main <main@ap-gto.groups.io>
Sent: Thu, Apr 16, 2020 4:25 pm
Subject: Re: [ap-gto] RAPAS on Mach2

“Hi Wade, peace..  just trying to understand.”
 
No problem.  Likewise, I’m just trying to offer some suggestions.
 
I tend to be overly verbose when I write, which probably overcomplicates things.  It probably wasn’t clear, but I’ve ever even used an eyepiece with my two main imaging scopes.  Everything that I’ve suggested is intended to be “imaging rig friendly” and fairly simple to do.
 
Regarding your previous attempts to image unguided, what kind of scope are you using?  I do most of my imaging with an EdgeHD 8, and I simply cannot do unguided imaging with it with any kind of regularity.  The issue is that the primary mirror just has too much movement, even with the focus clutches locked.  There is obvious star trailing after 3 minutes, and 5 minute subs are completely unusable to me.  I have to use an OAG.  An APPM model doesn’t really help a lot with this because the mirror movement seems to be non-repeatable.
 
When you do an APPM run, how much of the time is spent waiting for the image to download?  I was using a CMOS camera with USB 3 downloads for a while, and it would download a 1x1 frame in just a couple of seconds.  My current camera is a CCD with USB 2, and it takes a *long* time to download a 1x1 frame.  To mitigate this, I do 5 second exposures with 2x2 binning whenever I plate solve (either inside of SGP or with APPM).  That speeds things up considerably.  I spend less than an hour to get 100-150 points.  I suspect that your DSLR can probably download a lower resolution as well.  The last time that I binned a DSLR was many years ago with a Canon 20D, and it lost the Bayer matrix information when binned 2x2, but that was no big deal for plate solving.
 
My personal opinion that is unguided imaging is not something that interests me much.  It takes me about an hour to really dial in a new guider (what with focusing through my OAG and such), but once I’ve done that, it’s all automatic.  Since I always set up with the camera, OAG and guider at the same orientation, I don’t even need to recalibrate the guide software after setting up.
 
-Wade
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 1:57 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2
 
Hi Wade, peace..  just trying to understand.    Like I said in my original post, it may be that I'm just seeking something that isn't really practical or possible.   I have a full guiding setup, but when I get these posts using encoder mounts or my mount, showing incredibly flat controlled tracking, I'm trying to see if I can achieve this as well.     

I see the same things in forums, on claims of incredibly precise polar alignment, and as I said in the previous post, I don't know how they can make such claims.  I spent an hour one night polar drift alignment and had better alignment than usual, but it took an hour, and it still wasn't good enough for very long subs.   Long subs for me, with a CMOS camera, are still under 10 minutes or less.  I've done 20 minutes, but it's unusual.   Most of my subs are 1 minute (luminosity).    Although, having purchased some chroma 3nm filters, those seem to take some really long exposures to get a good amount of signal!

I measure drift in PHD2, using their drift alignment tool.. which takes forever to settle.. so it's a long process (for me).   Usually when I'm doing  polar alignment, I'm set up with camera, filter wheel, etc.. and want to do something that doesn't require me to take it apart and put in an eyepiece.    And PHD2 also gives me an estimate of my polar alignment error, which is based on drift, not instantaneous bouncing around the mean which I understand is all atmosphere.

I've only done one model, a 35 point small model, and I think it took around 25 minutes (it's been a while since clear skies).    And most of the plate solves were pretty fast.    I noticed the meridian points, solved twice, and most others once, so it does more than 35 solves for 35 points.    I use SGPro, which seems a bit slow to download files from my camera, which may make it slower than others.    The results of the 35 point model did not allow 1 minute subs, and I had unacceptably elongated stars.      But that's one data point,  and there is a lot to learn.  


Terri


Mike Shade
 

Using the traditional drift alignment method with an illuminated reticle eyepiece, I get round stars near the zenith with my first generation 1600GTO with a five minute unguided exposure, PEC on.  This is with a Planewave CDK 17, 2940mm fl, image scale .63"/pixel, permanent observatory setup.  Never had much use for or luck with software assisted polar alignment, although some people do.  Many years ago I had one of the red robotic mounts from "the other guys" and used their polar alignment program built into their pointing program.  Never seemed to give the same answers though.  The drift does take a bit though but as it is something I check about once a year, not that big of a deal.

 

Mike J. Shade

Mike J. Shade Photography:

mshadephotography.com

 

In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

Sir Winston Churchill

Already, in the gathering dusk, a few of the stars are turning on their lights.

Vega, the brightest one, is now dropping towards the west.  Can it be half

a year since I watched her April rising in the east?  Low in the southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights

 

International Dark Sky Association: www.darksky.org

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of W Hilmo
Sent: Thursday, April 16, 2020 1:15 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

Honestly, I’ve never measured my polar alignment error.

 

Beyond that, I don’t even know how to measure it in a way that would be useful in conversation.  I don’t know if you follow Cloudy Nights or not, but there is a near obsession over there with polar alignment.  I’ve seen people making polar alignment error claims that border on the ridiculous (like people claiming to be within 5” of the pole, etc.)  The drift from a 5” polar alignment error would be so small that I don’t know how you could detect it with a single exposure.  I would think that looking at the total field rotation for an entire night would be a better way to try and see a very small error.  I am pretty sure that people are just running some tool like a PoleMaster or SharpCap and just repeating what the software claims.  The thing is, that the software claims are not repeatable, even in the same session.  It’s made even more confusing because I am pretty sure that different software packages calculate the polar alignment error differently.

 

Even with PEMPro, which is the gold standard for software aided drift alignments, I can watch the calculated error bounce around by some number of arc seconds with each exposure, just due to seeing effects.

 

I take a more pragmatic view.  If I don’t get any noticeable drift in a single sub, and if I don’t get any field rotation over a night of imaging the same object, then I’ll call the polar alignment “good enough”.  If your goal is to do longish exposures unguided, especially at a longer focal length, then I would probably do it one of two ways:  If you take the time to run APCC, an APPM model will compensate for any polar misalignment, as well as drift from other factors (as long as they are repeatable).  That would be my preferred method.  If I didn’t want to do an APPM run for some reason, then I would do the RA Drift Alignment that’s described on the Astro-Physics site at the below link.  To do it, I would run PHD2 with my main imaging camera and guide corrections disabled.  This would give me a graph of the guide star during tracking that I could use to know which corrections to make:

 

https://astro-physics.info/tech_support/mounts/drift-alignment-ra-correction-method.pdf

 

The other option, that is new to the keypad firmware that will be available for the Mach2, will be that you can get tracking compensation right from the keypad (and it will also be available for the CP4).  I don’t believe that any of us have that keypad firmware yet, so I don’t know of anyone outside of the Astro-Physics folks that have first hand experience with it.  If I understand what I’ve heard correctly, it will work by calibrating on a couple of stars in the path of your object and building custom tracking rates for your specific target.  I’m guessing that it will be pretty effective.

 

At the end of the day, I believe that it’s important to understand a few methods to do an  effective polar alignment and also to not obsess over it.

 

In the meantime, how do you know that your polar alignment is causing problematic drift?  If the Mach2 ships with PEMPro, I would suggest that you start its polar alignment wizard and let it track for a while.  It will clearly show you any drift (and offer the change to make an adjustment to correct it).  If you don’t have PEMPro, then you can do a similar thing with PHD2 (as I described above, using it to facilitate a drift alignment).

 

And finally, I want to close the loop on a comment that I made earlier about my personal workflow at field sites.  I mentioned that I do both a daytime polar alignment and also use the RAPAS to tweak it.  The purpose of the daytime polar alignment is to get the mount reasonably close to polar aligned before it starts to get dark.  That way, when it gets to be dusk, you are pretty much guaranteed that Polaris will be both inside the view of the RAPAS and also obvious.  If you wait until after dark and start with the RAPAS, it can be tricky to find Polaris correct, especially if it lands outside of the RAPAS field of view.  In that case, it takes longer than 30 seconds (and I’ve seen more than one person polar align to Kochab in that scenario).

 

Hope that you find this information useful,

-Wade

 

 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 12:30 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

Thanks W Hilmo,

Not sure I ever see field rotation with any of my gross polar alignment methods.  I think you'd have to be pretty far off to see field rotation (but honestly don't know what that would be).  I'm trying to understand what kind of measured repeatable polar alignment people get.    Is 2 minutes, 3 minutes?   30 seconds?   With Polemaster, it's advertised at 30", and I see all kinds of claims on-line (hard to believe claims.. and claims that would be hard to even measure), but who knows.  Maybe I am just the worst polar aligner ever.    If I can do an accurate polar alignment (30") in 30 seconds, I will be exceptionally happy!!   I've never tried the daytime polar alignment.


Terri


Terri Zittritsch
 

On Thu, Apr 16, 2020 at 05:25 PM, W Hilmo wrote:

No problem.  Likewise, I’m just trying to offer some suggestions.

Wade, I appreciate the calm dialog.    Thank you.

I tend to be overly verbose when I write, which probably overcomplicates things.  It probably wasn’t clear, but I’ve ever even used an eyepiece with my two main imaging scopes.  Everything that I’ve suggested is intended to be “imaging rig friendly” and fairly simple to do.

No worries.   

Regarding your previous attempts to image unguided, what kind of scope are you using?  I do most of my imaging with an EdgeHD 8, and I simply cannot do unguided imaging with it with any kind of regularity.  The issue is that the primary mirror just has too much movement, even with the focus clutches locked.  There is obvious star trailing after 3 minutes, and 5 minute subs are completely unusable to me.  I have to use an OAG.  An APPM model doesn’t really help a lot with this because the mirror movement seems to be non-repeatable.



I have numerous scopes, but most recently it's been a Stowaway and a TEC140.  The Stowaway was being used at only 492mm , with reducer/corrector while the Tec was being used at, I think plate solving thinks it's 1037mm.    I use the A-P corrector which seems to increase the focal length a little.   

I started AP with an SCT 'Franken-rig'  with lightweight wedge, fork, and a wild assortment of weights to balance the whole thing.  I ended up with OK images.   Once I bought an Atlas, I deforked the meade 8" and ended up with much rounder stars.   That lightweight wedge only had to be breathed on and it would wobble... a huge challenge. but I always got it to work.    With the Meade 8" on the Atlas, my primary exposure was 5 minutes, unless I was imaging something really bright, where I might reduce to 2 or 3 minutes, or really dim, and I'd go to 6 minutes.   I was able to do acceptable work there, although I can do much better now.   My SCT had no mirror lock, and it worked acceptably well.  My Meade didn't have any mirror shift either (I must have been lucky).    I have since re-forked it now, and use it for outreach a lot.. it gives amazing views in a small package.    In fact, usually better views than most of the clubs 10" reflectors, and one 12",  they bring to the events.    Before anyone poo-poos this, they aren't Lockwood mirror scopes, but at least one is done by a local mirror grinding pro, and my SCT gives them a run for their money.
I use a 400mm Orion guide scope and lode star with the TEC140.   With the Stowaway, I have a 240mm guidescope with AS290 (small pixels) for better guiding resolution, or so I think.





When you do an APPM run, how much of the time is spent waiting for the image to download?  I was using a CMOS camera with USB 3 downloads for a while, and it would download a 1x1 frame in just a couple of seconds.  My current camera is a CCD with USB 2, and it takes a *long* time to download a 1x1 frame.  To mitigate this, I do 5 second exposures with 2x2 binning whenever I plate solve (either inside of SGP or with APPM).  That speeds things up considerably.  I spend less than an hour to get 100-150 points.  I suspect that your DSLR can probably download a lower resolution as well.  The last time that I binned a DSLR was many years ago with a Canon 20D, and it lost the Bayer matrix information when binned 2x2, but that was no big deal for plate solving.


I do need to try binning, I do 1x1 today, and use an ASI1600 or an ASI071.   I stopped using DSLRs around 18 mo. or so ago.   So it does takes far too long.. much longer than USB3 would indicate it should.  Many people complain about this on SGPro, but they've not been able to fix it, or it's a driver issue and I've stopped following the discussion.     It is what it is at this point, and for AP it's not a huge deal.    I should try 2x2 binning, and even thought it's all software, maybe i'll result in smaller file transfer if the downsizing happens in the camera.  If it happens at the computer, not much to be gained.   CMOS sensors do not bin in the same sense that CCD sensors do.    Once the image is at the computer, the plate solve is quite fast and usually after the first solve, they all happen very fast.

My personal opinion that is unguided imaging is not something that interests me much.  It takes me about an hour to really dial in a new guider (what with focusing through my OAG and such), but once I’ve done that, it’s all automatic.  Since I always set up with the camera, OAG and guider at the same orientation, I don’t even need to recalibrate the guide software after setting up.


At this point just trying to see what the high performance of the mount gets me.   I know it's made much better than my Atlas's (I have an old and new pro belt drive), but so far I've not been able to get significant and consistently better performance.   My last time out, I was imaging M101 and my RMS was .64 arc sec and M101 is pretty high in the sky.    I acknowledge it could be all seeing too, so my wanting better performance could be a pipe dream.     It could be that living in Vermont I should have taken up a more reliable hobby, like quilting, rather than astrophotography given our lack of clear and stable skies.     But I am a gluten for punishment.   Most of my AP is done in the dead of winter, unshielded by walls or an observatory in frigid weather (certainly not a sissy... smile) and dealing with at least one gotcha a night that requires some amount of debug.  I guess if the Mach2 gets rid of the gotchas, it'll be an improvement.  

I am an EE semiconductor engineer myself, so I have a fondness for finely made mechanical things..   It is pretty!   



Terri




Terri Zittritsch
 

On Thu, Apr 16, 2020 at 06:45 PM, Mike Shade wrote:
Using the traditional drift alignment method with an illuminated reticle eyepiece, I get round stars near the zenith with my first generation 1600GTO with a five minute unguided exposure, PEC on.  This is with a Planewave CDK 17, 2940mm fl, image scale .63"/pixel, permanent observatory setup.  Never had much use for or luck with software assisted polar alignment, although some people do.  Many years ago I had one of the red robotic mounts from "the other guys" and used their polar alignment program built into their pointing program.  Never seemed to give the same answers though.  The drift does take a bit though but as it is something I check about once a year, not that big of a deal.

Mike,
That is impressive!     This is what I want.. a once a year checkup on polar alignment!     The Planewave's are also something I've had my eye on!    We were planning to find a place with 10-20 acres this spring, and covid has put a damper on our moving for the time being.     Before the Planewave, I need an observatory!


Terri


Mike Shade
 

Thanks...the old method of drifting is a major pain but seems to work well for me and my setup.  It seems to change ever so slightly over the year, likely metal heat cycling in the AZ summer heat.  The PW 17 is a workhorse, when I check polar alignment I also check collimation.  That seems to hold pretty well, haven't had to tweak in a bit.  I also have AP scopes as well, those are cycle off and on of my old 1200GTO.

 

Curious as to where you were thinking of looking for property...that might be a topic for off-list though.

 

Mike J. Shade

Mike J. Shade Photography:

mshadephotography.com

 

In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

Sir Winston Churchill

Already, in the gathering dusk, a few of the stars are turning on their lights.

Vega, the brightest one, is now dropping towards the west.  Can it be half

a year since I watched her April rising in the east?  Low in the southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights

 

International Dark Sky Association: www.darksky.org

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 3:59 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] RAPAS on Mach2

 

On Thu, Apr 16, 2020 at 06:45 PM, Mike Shade wrote:

Using the traditional drift alignment method with an illuminated reticle eyepiece, I get round stars near the zenith with my first generation 1600GTO with a five minute unguided exposure, PEC on.  This is with a Planewave CDK 17, 2940mm fl, image scale .63"/pixel, permanent observatory setup.  Never had much use for or luck with software assisted polar alignment, although some people do.  Many years ago I had one of the red robotic mounts from "the other guys" and used their polar alignment program built into their pointing program.  Never seemed to give the same answers though.  The drift does take a bit though but as it is something I check about once a year, not that big of a deal.

Mike,
That is impressive!     This is what I want.. a once a year checkup on polar alignment!     The Planewave's are also something I've had my eye on!    We were planning to find a place with 10-20 acres this spring, and covid has put a damper on our moving for the time being.     Before the Planewave, I need an observatory!


Terri


Terri Zittritsch
 

For those that followed this and might be considering a polemaster, and noted that I wasn't getting the result I expected, I think I've figured out why I was seeing such a poor result.     When I started using the polemaster, it was with my Atlas mounts, and given I always need to do guiding, I didn't much worry about whether I was exactly on the pole or not, and didn't bother with drift measurements.. and guiding seemed to work just fine.   And as I recall, I was always on the 2nd step for both gain and exposure time.    Fast forward to getting the Mach2.  Now I'm trying to evaluate the performance of the Mach2, so wanting to do a more accurate polar alignment, and get it done early in the evening.   So I moved to the lowest setting on gain and exposure time (screen becomes viewable earlier).. I could always see the stars, but they were dimmer and smaller, and my thinking is that smaller is better for more accurate alignment.     But, for last step, the fine adjustment monitor step (going from 5-6 arc min alignment to 30" alignment) Polemaster actually picks up some other dimmer stars..   I believe when I decreased my gain and exposure times, these stars weren't being picked up reliably in the monitor step.  
To cut off the story,I think I was basically staying at the 5-6 arc minute gross polar alignment, which is essentially what I was measuring in PHD2.   After thinking about it, I decided to go back to the higher gain and exposure time to see if it made a difference.     This past weekend, I upped the gain and exposure time on the camera, did my polar alignment, and I noted that the monitor step adjustment required more tweaking than it had needed in prior mach2 polar alignments.     In checking my drift in PHD2... I had essentially zero.   Curve jumping around due to atmosphere, but no trend whatsoever over at least 5 minutes.   

So for anyone else who's had trouble getting better than the advertised gross polar alignment on the polemaster, this could be your issue.


T
 


Wayne Hixson
 

Very smart deduction! Thanks! 


On Apr 20, 2020, at 6:56 AM, Terri Zittritsch <theresamarie11@...> wrote:

For those that followed this and might be considering a polemaster, and noted that I wasn't getting the result I expected, I think I've figured out why I was seeing such a poor result.     When I started using the polemaster, it was with my Atlas mounts, and given I always need to do guiding, I didn't much worry about whether I was exactly on the pole or not, and didn't bother with drift measurements.. and guiding seemed to work just fine.   And as I recall, I was always on the 2nd step for both gain and exposure time.    Fast forward to getting the Mach2.  Now I'm trying to evaluate the performance of the Mach2, so wanting to do a more accurate polar alignment, and get it done early in the evening.   So I moved to the lowest setting on gain and exposure time (screen becomes viewable earlier).. I could always see the stars, but they were dimmer and smaller, and my thinking is that smaller is better for more accurate alignment.     But, for last step, the fine adjustment monitor step (going from 5-6 arc min alignment to 30" alignment) Polemaster actually picks up some other dimmer stars..   I believe when I decreased my gain and exposure times, these stars weren't being picked up reliably in the monitor step.  
To cut off the story,I think I was basically staying at the 5-6 arc minute gross polar alignment, which is essentially what I was measuring in PHD2.   After thinking about it, I decided to go back to the higher gain and exposure time to see if it made a difference.     This past weekend, I upped the gain and exposure time on the camera, did my polar alignment, and I noted that the monitor step adjustment required more tweaking than it had needed in prior mach2 polar alignments.     In checking my drift in PHD2... I had essentially zero.   Curve jumping around due to atmosphere, but no trend whatsoever over at least 5 minutes.   

So for anyone else who's had trouble getting better than the advertised gross polar alignment on the polemaster, this could be your issue.


T
 


Bill Long
 

For what its worth -- I used a polemaster and never found it to work very well, other than a rough alignment tool. I have had better results with a RAPAS unit that was calibrated after a PEMPro alignment was completed. That does a great job of getting me aligned quickly, and easily. Well before Polemaster can even display stars.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Wayne Hixson via groups.io <wayneh9026@...>
Sent: Monday, April 20, 2020 8:32 AM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] RAPAS on Mach2
 
Very smart deduction! Thanks! 


On Apr 20, 2020, at 6:56 AM, Terri Zittritsch <theresamarie11@...> wrote:

For those that followed this and might be considering a polemaster, and noted that I wasn't getting the result I expected, I think I've figured out why I was seeing such a poor result.     When I started using the polemaster, it was with my Atlas mounts, and given I always need to do guiding, I didn't much worry about whether I was exactly on the pole or not, and didn't bother with drift measurements.. and guiding seemed to work just fine.   And as I recall, I was always on the 2nd step for both gain and exposure time.    Fast forward to getting the Mach2.  Now I'm trying to evaluate the performance of the Mach2, so wanting to do a more accurate polar alignment, and get it done early in the evening.   So I moved to the lowest setting on gain and exposure time (screen becomes viewable earlier).. I could always see the stars, but they were dimmer and smaller, and my thinking is that smaller is better for more accurate alignment.     But, for last step, the fine adjustment monitor step (going from 5-6 arc min alignment to 30" alignment) Polemaster actually picks up some other dimmer stars..   I believe when I decreased my gain and exposure times, these stars weren't being picked up reliably in the monitor step.  
To cut off the story,I think I was basically staying at the 5-6 arc minute gross polar alignment, which is essentially what I was measuring in PHD2.   After thinking about it, I decided to go back to the higher gain and exposure time to see if it made a difference.     This past weekend, I upped the gain and exposure time on the camera, did my polar alignment, and I noted that the monitor step adjustment required more tweaking than it had needed in prior mach2 polar alignments.     In checking my drift in PHD2... I had essentially zero.   Curve jumping around due to atmosphere, but no trend whatsoever over at least 5 minutes.   

So for anyone else who's had trouble getting better than the advertised gross polar alignment on the polemaster, this could be your issue.


T
 


Terri Zittritsch
 

For what its worth -- I used a polemaster and never found it to work very well, other than a rough alignment tool. I have had better results with a RAPAS unit that was calibrated after a PEMPro alignment was completed. That does a great job of getting me aligned quickly, and easily. Well before Polemaster can even display stars.

I now have a RAPAS as well.    It's hard to know the accuracy difference, and how close you can eyeball it but the only way to do a good polar align without a computer.    I'll report back once I've adjusted the RAPAS holder after another good polar alignment.   The polemaster does require it to be darker out, especially at the higher gain settings that I seem to need to lock onto the fine adjustment stars.   I'm hopeful my experience over the past weekend is repeatable.

T


Greg Salyer
 

Terri, I had the same experience with PoleMaster. Just couldn’t get it closer than about 8’. However, I later found that my scope was slightly skewed from the mount. I suspect that was the problem. I fixed it but haven’t tried PoleMaster since. I just don’t want to take a chance of messing up the alignment I achieved with PEMPro.

Greg

On Apr 20, 2020, at 1:15 PM, Terri Zittritsch <theresamarie11@...> wrote:


For what its worth -- I used a polemaster and never found it to work very well, other than a rough alignment tool. I have had better results with a RAPAS unit that was calibrated after a PEMPro alignment was completed. That does a great job of getting me aligned quickly, and easily. Well before Polemaster can even display stars.

I now have a RAPAS as well.    It's hard to know the accuracy difference, and how close you can eyeball it but the only way to do a good polar align without a computer.    I'll report back once I've adjusted the RAPAS holder after another good polar alignment.   The polemaster does require it to be darker out, especially at the higher gain settings that I seem to need to lock onto the fine adjustment stars.   I'm hopeful my experience over the past weekend is repeatable.

T