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10micron mount testing


alan4908

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I've had my NEQ6 since I started astrophotography 3 years ago and overall I've been very impressed with its performance and particularly its ability to be integrated into my ACP controlled, automated imaging observatory set up.  

Since the UK has relatively few clear nights, I decided to purchase a new mount that would (hopefully) increase my DSO acquisition efficiency. I also wanted a mount that would also allow a heavier imaging payload since I was also planning to acquire a long focal length APO refactor to complement my existing SW 80 ED.  In selecting a new mount, I decided to look through my ACP logs where I discovered that that guiding errors where my number one cause of lost subs.  I also noticed that it took ACP quite a time to acquire a suitable guide star, wait for the guider to settle and actually begin guiding.  Very occasionally, I had also experienced the mount losing its park position when powered up.  Since my telescope can hit the observatory roof this was somewhat alarming and so I always made sure that I was physically present whenever powering up the mount.  

After taking into consideration all of the above, I decided to buy a 10micron GM1000HPS, mainly because of its ability to acquire long exposure unguided subs. I also liked the fact that it had absolute encoders and so, should always know its relative sky position.

The tracking of the 10micron mount is based on the principals of telescope pointing by Patrick Wallace (http://www.tpointsw.uk/pointing.htm) with 10micron having developed a proprietary algorithm for solving the various equations that model the telescope.

The first thing that I discovered is that unlike a normal equatorial mount, you can obtain much better results if your pier is level rather than approximately level.  I also discovered that tracking could be further improved if you had quite an accurate polar alignment. By contrast, tracking appears relatively insensitive to orthogonality error. For those that might be interested I eventually settled on a polar alignment error of 43 arc seconds and an orthogonality error of just over 16 arc minutes. 

To solve the various equations that allow the telescope to point and accurately track you have to build a sky model, you can either do this manually or automatically using various sky model making software options. Having chosen to go down the automated route with Per's Model Maker, I eventually built a model with 41 points and achieved a RMS of 2 arc seconds having deleted two outlying points.  In the course of my various attempts at model building, I noticed that the placement of the first three points (base points) is critical. These need to be equally spaced, cover both sides of the meridian and vary slightly in altitude (I choose around 50 degrees).  I also discovered that I could get a lower final RMS if I modeled the two half's of the meridian separately with the refinement points.  I presume this because the mount is slewing less and hence introducing less random errors. 

I currently plan to pursue two issues:

1. When the mount tracks across the sky, it does so in both RA and DEC - 10micron call this dual tracking. What is confusing is that the user manual implies that the dual tracking should be on during the making of the sky model, so lots of people over the years appear to have built models with the dual tracking on. Baader Planetarium (the European 10micron distributor) has recently stated that dual tracking needs to be off during model building or polar alignment. I'd therefore be interested to know from anyone or has done a comparison test between the two approaches. 

2. After you've built a model and want to come back to it several days later and nothing has changed - you are only supposed to perform one synch align (which apparently sets the encoder offsets). I've tried this in ACP and I obtain very poor results. However, if I resynch after each acquired image I get very good results apart from the first image which has elongated stars. I have a theory that where you choose to perform the synch align is critical and is dependent on the model you have built. Anyway, I'd be interested to hear from anyone who has managed to get this to work. 

So, having built the sky model, I decided to try it out. Rather than focusing on random objects, I decided to pick NGC2276 mainly because it was always visible from my location at this time of the year and also because it was well above 30 degrees altitude, hence refraction effects would be minimized. My initial test LRGB result is below which consists of 10min subs, the vast majority of which have aspect ratios of between 4 and 12 (as measured by CCD Inspector), my quality threshold is 15, so I'm very pleased with my first attempt at unguided imaging.

Alan

58d7ee7281b5c_7.Final.thumb.jpg.a42dc3b4f34cc92c271edfbed50b0279.jpg

 

 58d7eeaf8493b_7_FinalNGC2276Annotated.thumb.jpg.46ea75a70e7fa36888c36e2a3888cc1a.jpg

 

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1 hour ago, alan4908 said:

1. When the mount tracks across the sky, it does so in both RA and DEC - 10micron call this dual tracking. What is confusing is that the user manual implies that the dual tracking should be on during the making of the sky model, so lots of people over the years appear to have built models with the dual tracking on. Baader Planetarium (the European 10micron distributor) has recently stated that dual tracking needs to be off during model building or polar alignment. I'd therefore be interested to know from anyone or has done a comparison test between the two approaches. 

I have only ever carried out model building with dual tracking on following 10 Micron's manual - I get good RMS after optimisation enabling me to image unguided upto 30mins without issue.  So why bother changing?  It works.  I don't understand the comment made by Baader as reported on the 10 Micron forum.  The level base and tripod is important for the first base points to help with goto accuracy/synching refine before carrying out PA, AFAIK.

1 hour ago, alan4908 said:

After you've built a model and want to come back to it several days later and nothing has changed - you are only supposed to perform one synch align (which apparently sets the encoder offsets). I've tried this in ACP and I obtain very poor results. However, if I resynch after each acquired image I get very good results apart from the first image which has elongated stars. I have a theory that where you choose to perform the synch align is critical and is dependent on the model you have built. Anyway, I'd be interested to hear from anyone who has managed to get this to work. 

I use SGP and will synch align from time-to-time wherever the mount is pointing and as part of its slew/centre routine (including meridian flips) and have not noticed any deterioration in pointing accuracy or unguided performance dependent on synch position.  I have synch aligned after not imaging for weeks this winter (with 925mm FL) and imaged unguided without problem and have only ever been a few pixels off target, circa 20 or so, on the first slew before synch align.

Having a comprehensive pointing model that covers much of the sky over your chosen altitude (say 45 or 50 degs) helps with this of course.  If you haven't yet done so, I would encourage you to build a 90+ point model.  I agree with you in that I have achieved better results with sorting my points E and W of the meridian (and by altitude) and carefully choosing my 3 base points spread 120 deg apart (and importantly not on the meridian or under the pole where plate solving can be inaccurate) and at say 50 deg.  Good focus, equalised optics with the temp, good time synch, refraction enabled, long-enough subs to get good images (say 5 or 6 secs, bin 2), perfect balance, no cable drag, no flexure, reducing cone error with shimming if needed, settle for a couple of secs after slewing - all techniques of good practise regardless of your mount really.

I can't emphasis enough that I've found these AP points to be just as important with the 10 Micron as any other mount if you desire good and durable unguided performance.  In fact the 10Micron has really helped me focus on the importance of attention to technique all-round.

I'm sure you've realised the 10 Micron forum is a good resource and everyone is very helpful and there certainly are some very talented and generous folks, able to build hardware and software to share with the 10 Micron community.

Happy to be a sounding board via PM if you ever need it Alan.

CS!

Barry

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2 hours ago, Barry-Wilson said:

I have only ever carried out model building with dual tracking on following 10 Micron's manual - I get good RMS after optimisation enabling me to image unguided upto 30mins without issue.  So why bother changing?  It works.  I don't understand the comment made by Baader as reported on the 10 Micron forum.  The level base and tripod is important for the first base points to help with goto accuracy/synching refine before carrying out PA, AFAIK.

Yes the comment from Baader on dual tracking is a little strange. Since Baader are a respected company, my working assumption is that it will improve matters, but probably by only a small amount.  Baader have now produced a document which clearly states this which I attach for your information.  

2 hours ago, Barry-Wilson said:

I use SGP and will synch align from time-to-time wherever the mount is pointing and as part of its slew/centre routine (including meridian flips) and have not noticed any deterioration in pointing accuracy or unguided performance dependent on synch position.  I have synch aligned after not imaging for weeks this winter (with 925mm FL) and imaged unguided without problem and have only ever been a few pixels off target, circa 20 or so, on the first slew before synch align.

Having a comprehensive pointing model that covers much of the sky over your chosen altitude (say 45 or 50 degs) helps with this of course.  If you haven't yet done so, I would encourage you to build a 90+ point model.  I agree with you in that I have achieved better results with sorting my points E and W of the meridian (and by altitude) and carefully choosing my 3 base points spread 120 deg apart (and importantly not on the meridian or under the pole where plate solving can be inaccurate) and at say 50 deg.  Good focus, equalised optics with the temp, good time synch, refraction enabled, long-enough subs to get good images (say 5 or 6 secs, bin 2), perfect balance, no cable drag, no flexure, reducing cone error with shimming if needed, settle for a couple of secs after slewing - all techniques of good practise regardless of your mount really.

I can't emphasis enough that I've found these AP points to be just as important with the 10 Micron as any other mount if you desire good and durable unguided performance.  In fact the 10Micron has really helped me focus on the importance of attention to technique all-round.

I'm sure you've realised the 10 Micron forum is a good resource and everyone is very helpful and there certainly are some very talented and generous folks, able to build hardware and software to share with the 10 Micron community.

Happy to be a sounding board via PM if you ever need it Alan.

It is encouraging to see the synch aligns working for you, Barry.  If I've understood the purpose of the synch align correctly, I cannot see the disadvantage of performing this after each image acquisition. 

I have just (whilst typing this ) created a 97 point model (with dual tracking off  :happy11:) and deleted 3 outlying points, 2 off which where associated with the 3 base points. I'm following all your other points with the exception of the orthogonality error (which is currently estimated at 13 arc minutes with my new model). I haven't yet received my mbox yet, so I'm having to enter temperatures manually to compensate for refraction effects.

I may well take you on your offer as a sounding board via PM.....I'll first see what the results are like with my new model.

Alan

 

EN_HPS_quickstart-manual_A5_RGB_LR_0317-3.pdf

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I managed to get a few subs with the new sky model I built with dual tracking switched off. This takes onboard Barry's suggestion of increasing the number of points in the skymodel to over 90 and covering all the sky that I would be imaging. 

The synch align issues which I was previously experiencing appear to have disappeared with everything now apparently working with just one initial synch align with ACP.

Although the night was a bit cloudy, I decided to try out a one hour single exposure on M106.  To ensure that the stars did not become bloated I used my 3mn Ha filter. CCDInspector reports that the average star aspect ratio is 10, the uncalibrated result is below.

So, it all looks very promising, all I need now is a few more clear nights to confirm everything is OK :hello:

Alan

M106: 3600s single sub unguided - 3nm Ha

58d909f87f15d_M106H3600s.thumb.jpg.adb437db07a5728abb5056963e9f4d07.jpg

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Thank you Alan for the link to the Baader leaflet: it does seem odd that the 10 Micron manual and this leaflet contain contradictary info.  Perhaps post up the leaflet on the 10 Micron forum for members to see and arrive at their own judgement.  Did you notice any benefit from building the model without dual axis encoders enabled?  What was your resultant RMS?  I find that getting below 6" or 5" wil give good unguided imaging.  I often achieve below 4".

What a great success though with your new model and 60-minute sub - well done!  Image and stars look good.

The cone/orthogonal error on my 3 scopes varies between 1 and 3 arc minutes and I'm not sure if I'm exceptionally lucky and that is a low cone error or whether your 13 arc minutes is more typical or of moderate size.  Whatever, your pointing experience and centring post meridian flip will tell you whether you need to devote some time to reducing the cone error or if plate solving post flip negates the need :icon_biggrin:.

I have regularly imaged unguided at 20 and 30 minute for NB filters.  I have promised myself to capture some 60 min subs but do not have the chance at the moment as I'm capturing RGB on galaxy targets.

All the best, Barry

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I've always left dual-tracking enabled and not seen a problem, I also always use the maximum number of points available (97+3) well spread across my visible sky to generate the model. I had noticed a couple of years ago when testing various models that an apparent lower RMS may be obtained using fewer sample points but the better performance was to be had with the most complex model - so even though your RMS may be slightly higher using more points the resultant model is probably more realistic. With the refractor I get around 3 arcsec (best 2.5), my ODK12 is usually double that but still usable for unguided imaging.

I mentioned my StickStation died a couple weeks ago, it seems (best guess) one or more sensors have failed and it is returning invalid data. Every other function on it works OK - communication with the PC is fine, but when the App (or mountwizzard) tries to evaluate the incoming data it always causes a crash as the data is 'out of range'. So nothing to be done other than replace it and I'm also awaiting delviery of an MBox (don't need the GPS functionality as I already have that).

Your M106 result is impressive for a 60min unguided integration but being positioned where it is the mount is not very stressed - choosing a different target lower down along the ecliptic would offer more of a challenge I think. Anotehr good test is allowing a meridian flip without re-centering and checking how close you are to the original target co-ordinates. With the refractor it's bang-on accurate, with the ODK it would be a little out without re-centre. I haven't used my ODK12 for nearly a year but tonight it goes back on the mount - I expect all sorts of new problems to surface :)

ChrisH

Edit: Just put the gear away. I had a few problems to start out with - the first model was horrible - 78 arcsec RMS with a dozen failed plate solves. All the big errors were in DEC and I figure the balance wasn't quite right. Ran another model and it was better - RMS of 6 arcsec after removal of one point that was way out. Tracking looked to be good but I was only using 15min subs (2040mm focal length though). I'd forgotten just how heavy that ODK12 + camera etc., is to lift onto the mount :)

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18 hours ago, Barry-Wilson said:

Thank you Alan for the link to the Baader leaflet: it does seem odd that the 10 Micron manual and this leaflet contain contradictary info.  Perhaps post up the leaflet on the 10 Micron forum for members to see and arrive at their own judgement.  Did you notice any benefit from building the model without dual axis encoders enabled?  What was your resultant RMS?  I find that getting below 6" or 5" wil give good unguided imaging.  I often achieve below 4".

Feel free to post the leaflet anywhere you want since it's public information (it's only recently been completed by Baader). Unfortunately, I don't have any comparisons with dual axis enabled versus disabled during model building. With dual axis disabled, my model was 97 points at an 2.82 rms with 21 model terms. 

18 hours ago, Barry-Wilson said:

What a great success though with your new model and 60-minute sub - well done!  Image and stars look good.

Thanks - this is mainly due your suggestion of covering the sky with more points. :happy11:

18 hours ago, Barry-Wilson said:

The cone/orthogonal error on my 3 scopes varies between 1 and 3 arc minutes and I'm not sure if I'm exceptionally lucky and that is a low cone error or whether your 13 arc minutes is more typical or of moderate size.  Whatever, your pointing experience and centring post meridian flip will tell you whether you need to devote some time to reducing the cone error or if plate solving post flip negates the need

Your error is impressively low, I believe my orthogonality error should only impact pointing rather than tracking. Currently I instruct ACP to correct any pointing errors larger than 0.15 arc mins, by doing an autocenter without issuing a synch align, so I don't think this is something I need to test, however, correct me if you disagree !

 

18 hours ago, ChrisLX200 said:

Your M106 result is impressive for a 60min unguided integration but being positioned where it is the mount is not very stressed - choosing a different target lower down along the ecliptic would offer more of a challenge I think. Anotehr good test is allowing a meridian flip without re-centering and checking how close you are to the original target co-ordinates. With the refractor it's bang-on accurate, with the ODK it would be a little out without re-centre. I haven't used my ODK12 for nearly a year but tonight it goes back on the mount - I expect all sorts of new problems to surface :)

Chris - just to make sure that I understand your ecliptic comment correctly.  I think you are saying that the lower the DEC of the object the more difficult it will be to guide.  Since I like formulas to describe things, I found this one from Chris Woodhouse's  book "The Astrophography Manual" page 279:

Autoguider rate = 15.04 x guide rate x cos (DEC)/autoguider resolution (arcsec/pixel).

Since I'm not autoguiding, I presume I can modify the formula so: set the guide rate = 1 and the autoguider resolution will be my main camera resolution. So, the rate that the unguided mount will need to correct things will be determined by:

Mount correction rate = 15.04 x cos (DEC)/image resolution (arcsec/pix).

So, the lower the DEC angle or the smaller the image scale, the higher the correction rate,  is this what you mean ?

 

18 hours ago, ChrisLX200 said:

Anotehr good test is allowing a meridian flip without re-centering and checking how close you are to the original target co-ordinates. With the refractor it's bang-on accurate, with the ODK it would be a little out without re-centre.

Chris - just checking that I understand this - I presume this is test for orthogonality error rather than tracking. Is this correct ? (see also my comment above)

Anyway, since it was partially clear last night, I decided to have another go at some more 1 hour subs, again only using my 3nm H filter. Again, I decided to  only let ACP perform an initial synch align after it had performed the first autofocus of the evening. I only got three subs before the clouds rolled in and my observatory decided it had enough for the evening.

M81 - 3600s H uncalibrated (DEC:69 degrees, Elevation at Exposure start: 69 degrees)

58da41b413f81_M81H3600suncalibrated.thumb.jpg.01d32dfa51cb05a821a85729b7411912.jpg

M66 - 3600s H uncalibrated (DEC:13 degrees, Elevation at start of exposure: 46 degrees)

58da41f339bb8_M66H3600suncalibrated.thumb.jpg.2bbb37394b00606fa91602f3ee90a5bc.jpg

NGC4631 - 3600s H uncalibrated (DEC: 33 degrees, Elevation at start of exposure: 60 degrees)

58da42284881f_NGC4631H3600suncalibrated.thumb.jpg.7d327494c3a6837546e35ded00464cef.jpg

 

When I put these through CCD Inspector I get average Aspect Ratios of M81: 23; NGC4631: 9; M66:65. Clearly M66 is bin material and the formula above predicts that this would be most difficult to image.  What's interesting with the M81 sub is that when I look at the stars in the centre of the image with MaximDL's Information window, it is telling me that quite a few of the stars near the center have much smaller aspect ratios, maybe CCDI is getting a bit confused over the H regions which are quite bright.

I'm still intrigued to understand if the point where the initial synch align is performed has a subsequent impact on the tracking performance. Since the model error is not uniform in all directions (eg in my case an RMS 2.82 arc seconds is predicted), intuitively, I would have thought that it would matter. If this is correct, then presumably the optimum place to perform the synch align would be at that region of the model which has the lowest collection of pointing errors ? 

Any thoughts would be appreciated !

Alan  

 

 

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Perhaps I read it too simply - but the further away from the Pole you are imaging then the greater the apparent movement will be over time and hence increased potential for drift (tracking error) to show up on your sensor.

Also, if your OTA is not orthogonal then this should show up during a modelling run after the meridian flip, pointing errors on one side of the mount will differ (be offset) from the other side and you'll end up with 22 modelling terms instead of 11 (the mount has detected there is a difference between East and West sides of the pier and modelled each separately). I always get 11 terms using the refractor, and usually 22 (not always for some reason!) with the ODK12. I put that down to the ODK12 being less stable and also having larger cone error. I guess I should quote the model data to be sure but I cannot remember the numbers off hand :)

Your final point - yes, re-synching the model simply moves the whole thing using that single offset from the plate solve, if you re-synch (an extreme example) at a point close to the pole where the potential for a solving error (particularly in RA) is greatest then the rest of the points will be offset by the same error - not something you want to do. I suppose if you had to re-synch the model then using somewhere near DEC 0 would be better. Personally, using the refractor, I don't re-synch the model after removing and replacing the OTA on a subsequent night, I just made sure it goes back on the dovetail in exactly the same position. I can't do that with the ODK12 accurately enough (it's just too 'bendy' :) ) and although I tried I never found re-synching a model was successful in restoring pointing and tracking accuracy with the ODK12, so with that I need to re-run a new model each time I use it.

ChrisH

PS. My MBox arrived today! Works great :)

 

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1 hour ago, ChrisLX200 said:

Perhaps I read it too simply - but the further away from the Pole you are imaging then the greater the apparent movement will be over time and hence increased potential for drift (tracking error) to show up on your sensor.

Also, if your OTA is not orthogonal then this should show up during a modelling run after the meridian flip, pointing errors on one side of the mount will differ (be offset) from the other side and you'll end up with 22 modelling terms instead of 11 (the mount has detected there is a difference between East and West sides of the pier and modelled each separately). I always get 11 terms using the refractor, and usually 22 (not always for some reason!) with the ODK12. I put that down to the ODK12 being less stable and also having larger cone error. I guess I should quote the model data to be sure but I cannot remember the numbers off hand :)

Your final point - yes, re-synching the model simply moves the whole thing using that single offset from the plate solve, if you re-synch (an extreme example) at a point close to the pole where the potential for a solving error (particularly in RA) is greatest then the rest of the points will be offset by the same error - not something you want to do. I suppose if you had to re-synch the model then using somewhere near DEC 0 would be better. Personally, using the refractor, I don't re-synch the model after removing and replacing the OTA on a subsequent night, I just made sure it goes back on the dovetail in exactly the same position. I can't do that with the ODK12 accurately enough (it's just too 'bendy' :) ) and although I tried I never found re-synching a model was successful in restoring pointing and tracking accuracy with the ODK12, so with that I need to re-run a new model each time I use it.

ChrisH

PS. My MBox arrived today! Works great :)

Hi Chris

Thanks for the clarifications. Since, I have developed the habit of reflecting back (to check my understanding) :happy11:

On the orthogonality error - with my latest model I have 21 terms, so the two sides of the meridian are being modeled separately. I'm still not clear if you are saying that reducing my orthogonality error will improve my tracking or simply that this will improve my pointing accuracy or it will improve both tracking and pointing.:help:  The user manual states "In order to obtain optimal performance, it is not required to correct physically the orthogonality error".  It also states that "It is not necessary to correct physically the orthogonality error in order to obtain a good pointing accuracy or tracking".

On where to synch align - if I wish to resynch then you are suggesting synch aligning at a point where the plate solving would be most accurate eg somewhere near DEC 0, rather than where the where the model errors (visible in the model graph report) are the lowest.  

I'm still waiting for my mbox, it's good to see that it is working for you !

Alan

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