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A new Polar alignment technique using BYEOS


STEVE333

Question

Below is a link to a YouTube video showing how to do precise polar alignment using BYEOS.  The technique is easy, and, I hope it helps you as much as it has helped me.

 

https://www.youtube.com/watch?v=mZWEtAV1zCw

 

I have always achieved misalignment errors of less than 1 arc min with this technique with only one iteration.

 

Happy aligning!

 

Steve

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Hello Steve

 

  I had some time and clear skies last night.  I used your method for quick alignment and had the results described in your posts.

 

  I can't comment on how close the alignment was because visiting with neighbors and set-up goof-ups took up a lot of time.  I didn't get to spend too much time imaging to see how the PHD2 numbers were over a long time.  I did take a 7 minute guided exposure of M45 that came out good.

 

  I did have better numbers in in PHD 2 over last time I set up using your system.  Dec was below .5 arc seconds most of the time and total was below 2 arc seconds most of the time.  I will continue to use it and have a final evaluation at a later date.  I have several scenarios to try first.

 

Ron

Good news Ron.  Sound like it worked for you this time.  Thanks for taking the time to report your results.

 

FYI, if you want to see how good the alignment is you can do the following (no matter how you do your PA):

  1. Perform a normal PHD2 calibration and start guiding.
  2. Press Stop at the bottom of PHD2.
  3. Click on the "Brain" at the bottom of PHD2.
  • Click on the Algorithms tab.
  • Open the Dec guide mode dropdown list.
  • Click on Off to turn off Declination guiding.
  • Click OK to accept the changes.

When this is all done then start guiding again with PHD2 (no recalibration required).

On the guiding graph, make sure Corrections is unchecked and Trendlines is checked.

Allow the guiding to continue for at least 5 minutes to establish a good "Dec Drift Trend".

Along the middle of the graph PHD2 writes the estimated Polar alignment error (in arc minutes on my system).

 

Hope this is useful.

 

Steve

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Steve,

 

That is pretty much what PHD2's Drift Align does, but it leads you through the process, including positioning the mount at the optimum locations for adjusting azimuth and altitude.

Thanks Steve -

I believe PHD2's Drift Align is performed on two different stars (one at a time).  

With mine (as you found) you only need the three images and then one adjustment with the mount azimuth and altitude to position Polaris at the new cursor position and you are done.  I like not having to iterate between the two stars.

 

Thanks again for the feedback.  Still no imaging for me until my wife can put some weight on her recovering broken ankle, so, my AP enjoyment is all vicarious.

 

Steve

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Steve,

 

Sorry for any confusion. In your previous post you described how to check PA with PHD2. Your description is close to what is done during the drift align. Specifically, turn off declination guiding and monitor drift by watching the declination trendline. Yes, it does use 2 stars one star for adjusting the azimuth and the other for adjusting the altitude. As long as the PA is close there is no iteration between the 2 stars. Adjust the azimuth then adjust the altitude and you are done.

 

Thanks for posting!

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Steve,

 

Sorry for any confusion. In your previous post you described how to check PA with PHD2. Your description is close to what is done during the drift align. Specifically, turn off declination guiding and monitor drift by watching the declination trendline. Yes, it does use 2 stars one star for adjusting the azimuth and the other for adjusting the altitude. As long as the PA is close there is no iteration between the 2 stars. Adjust the azimuth then adjust the altitude and you are done.

 

Thanks for posting!

Thanks for the clarification Rick.

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Hi Steve

 

  OK  I took what I said from the PoleMaster requirement for the camera orientation when using atmospheric modeling.  I accept your explanation since you have been in up to your armpits getting this method right for those who want to try it and use it.  I keep saying thank you for developing this and posting it here because I mean it.  I have found it very helpful.

 

  I am steppinbg back from using QPPA for my Wedge mounted SCT for the moment.  I will start to try again in the future.  It is a lot of work to get the 10 inch set up and i get frustrated when things don't go so well or at least as well as I expect.  I have been able to get a good pooar alignment using the PoleMaster system.  But I haven't been able to set up the ST80 so I can apply the QPPA  procedure.  I will use one of my 135mm lens later on and see if it will give me results.  I will post my results when I get through.  It may be next year in early spring.

 

  Until I get to that point I will say that from my playing with both systems there isn't a lot of difference for those setting up nightly in the systems except that QPPA is less costly (Free).  If you have everything and run through the process 4 or 5 times to where it is nearly second natures you get similar results or at least I do.

 

  I have read your posts on Astronomy Now forum and I do have some interest in the software using guide scope and camera.  I think it was written primarily for the southern hemisphere.   I forgot who it was.  I don't socialize very well is the reason I haven't gotten on that forum.  The fact you have to sign up for social networking has kept me from signing up.

 

  Again Thank you for giving a simple stated clarification on some of the points.

 

  For those with observatories I am sure they will Drift align since they will walk into a well aligned telescope each time they go out at night.  They may want to use QPPA for star parties for initial alignment then drift align.

 

Ron

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Hi Steve

 

  OK  I took what I said from the PoleMaster requirement for the camera orientation when using atmospheric modeling.  I accept your explanation since you have been in up to your armpits getting this method right for those who want to try it and use it.  I keep saying thank you for developing this and posting it here because I mean it.  I have found it very helpful.

 

  I am steppinbg back from using QPPA for my Wedge mounted SCT for the moment.  I will start to try again in the future.  It is a lot of work to get the 10 inch set up and i get frustrated when things don't go so well or at least as well as I expect.  I have been able to get a good pooar alignment using the PoleMaster system.  But I haven't been able to set up the ST80 so I can apply the QPPA  procedure.  I will use one of my 135mm lens later on and see if it will give me results.  I will post my results when I get through.  It may be next year in early spring.

 

  Until I get to that point I will say that from my playing with both systems there isn't a lot of difference for those setting up nightly in the systems except that QPPA is less costly (Free).  If you have everything and run through the process 4 or 5 times to where it is nearly second natures you get similar results or at least I do.

 

  I have read your posts on Astronomy Now forum and I do have some interest in the software using guide scope and camera.  I think it was written primarily for the southern hemisphere.   I forgot who it was.  I don't socialize very well is the reason I haven't gotten on that forum.  The fact you have to sign up for social networking has kept me from signing up.

 

  Again Thank you for giving a simple stated clarification on some of the points.

 

  For those with observatories I am sure they will Drift align since they will walk into a well aligned telescope each time they go out at night.  They may want to use QPPA for star parties for initial alignment then drift align.

 

Ron

Very nice summary Ron.  Thanks for taking the time to share your results.

 

FYI I'm working on an "improved" version of QPPA.  I've added a correction for Atmospheric Refraction.  Even at my Lattitude of 37 deg the refraction correction is significant.  I've also found a way to do the correction that doesn't require any user input about the camera orientation.  You just need to input (once) some site information (Lattitude, Longitude, etc.) as well as the ambient temperature at the time of the calibration (colder denser air bends the light more than warmer air).  The new program is written in Visual Basic, so, Excel will no longer be required.  My son is visiting next week (he wrote the cursor program) and we might be able to combine my new version with his cursor so everything is all in just one program.  More to follow.

 

Steve

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Hi Steve,

That looks like an interesting program I'm looking forward to as well!

Eventhough I'm using a Polemaster, it will be of great help also to

my friends who don't have such a nice gadget.

For me the guiding is almost always < 0.4" on the PHD2 graph.

It could be better but I don't spend any time at all at balancing the

whole setup.

 

Regards and thanks for sharing with all of us!!

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You are right Rick, closer is definitely better.  Your alignment to within 5 arc-seconds is extremely good.  I'm very impressed.

 

The new PoleMaster that is so popular only promises to get to within 30 arc-seconds, but, it seems to be good enough for everyone so far.

 

The biggest problem with too large a misalignment will be image rotation for long exposures.  The guide system will correct for the slow Dec drift, but, it won't correct for the image rotation which, of course, leads to star tails.

 

Thanks for your responses.

 

Steve

 

Looking through the PHD2 forum, if you have a lot of DEC backlash closer may not always be better!

 

Andy Galasso frequently advises that for mounts with a lot of DEC backlash a small misalignment is advantageous so that DEC guiding can be set in one direction only. I.e. like RA guiding where the guide instructions (hopefully) only slow or speed up the motor, not make it change direction and therefore the backlash is not an issue. By having a slight misalignment it allows the DEC motor to also only be driven in one direction.

 

Obviously not having backlash would be best, but for most of us on reasonable and averagely priced mounts zero backlash is an aspiration more than a fact.

 

Jim

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Looking through the PHD2 forum, if you have a lot of DEC backlash closer may not always be better!

 

Andy Galasso frequently advises that for mounts with a lot of DEC backlash a small misalignment is advantageous so that DEC guiding can be set in one direction only. I.e. like RA guiding where the guide instructions (hopefully) only slow or speed up the motor, not make it change direction and therefore the backlash is not an issue. By having a slight misalignment it allows the DEC motor to also only be driven in one direction.

 

Obviously not having backlash would be best, but for most of us on reasonable and averagely priced mounts zero backlash is an aspiration more than a fact.

 

Jim

I've heard that too Jim.  Unfortunately, if I set the Dec guiding to one direction, then, I believe I can only DITHER in RA Only.  I've found that dithering in RA Only doesn't help as much with the noise as when I dither in both directions.  Sigh!!!  So many tradeoffs.

 

I've had my mount Backlash compensation set at 0000 so far and just let PHD2 do the compensation.  I'm going to try dialing in some mount backlash compensation and then try the GUIDING ASSISTANT again to see if it makes it better or worse.  I know most people say to turn off the mount backlash compensation so that PHD and the mount don't fight each other.  However, nothing to loose at this point, just a little time for the experiment.  With the mount backlash set to 0000 the Guiding Assistant says my Dec backlash is 7900 msec which is a lot!!

 

Steve

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 Hi Steve

 

  I have had my Meade SN6 out on three different nights to work with your QPPQ method.  Well the last three times, I can report I had a good alignment and had good guiding equal to any I have had before and I feel better in these three cases better.  PHD2 did give some readings that were beyond what I felt should have been .

 

  You mentioned Polemaster in one post and I was curious.  I did several searches and watched some of the Youtube videos.  I bought one.  I like it very much for being in a constant setup and tear down mode for my astronomy work.  Last night I used it to do the Polar alignment.  After that I used the QPPA method.  In the end QPPA had an adjustment of CORR x 11 and CORR y -49.  Looking at the image in the full page it wasn't much of an adjustment.  Clouds came in so I couldn't do a reverse of that, aligning with QPPA then Polemaster.  I will do that next time just for grins.

 

  Polemaster costs $300 or so and QPPA is free.  If you setup each time you go out and you aren't satisfied with your alignment then make a choice.  Both takes about the same amount of time.  Not a big enough difference to quibble over.  If you have a permanent observatory then you should have good alignment using drift.  You take the time because it will not need another drift for 6 months to a year.  You may wont to check in between but not a full drift alignment.

 

  Another interesting thing I heard on one presentation was that Polemaster determined its accuracy because the camera used had an  image scale at .3 arc seconds.  Since you said you felt you were getting close to 1 arc second I checked my 60Da image scale in CCD Calc and it is 1.16 arc second.

 

  I will use both for polar aligning depending on circumstances of where I set up.

 

  Thanks for making this available to the community.

 

Ron

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 Hi Steve

 

  I have had my Meade SN6 out on three different nights to work with your QPPQ method.  Well the last three times, I can report I had a good alignment and had good guiding equal to any I have had before and I feel better in these three cases better.  PHD2 did give some readings that were beyond what I felt should have been .

 

  You mentioned Polemaster in one post and I was curious.  I did several searches and watched some of the Youtube videos.  I bought one.  I like it very much for being in a constant setup and tear down mode for my astronomy work.  Last night I used it to do the Polar alignment.  After that I used the QPPA method.  In the end QPPA had an adjustment of CORR x 11 and CORR y -49.  Looking at the image in the full page it wasn't much of an adjustment.  Clouds came in so I couldn't do a reverse of that, aligning with QPPA then Polemaster.  I will do that next time just for grins.

 

  Polemaster costs $300 or so and QPPA is free.  If you setup each time you go out and you aren't satisfied with your alignment then make a choice.  Both takes about the same amount of time.  Not a big enough difference to quibble over.  If you have a permanent observatory then you should have good alignment using drift.  You take the time because it will not need another drift for 6 months to a year.  You may wont to check in between but not a full drift alignment.

 

  Another interesting thing I heard on one presentation was that Polemaster determined its accuracy because the camera used had an  image scale at .3 arc seconds.  Since you said you felt you were getting close to 1 arc second I checked my 60Da image scale in CCD Calc and it is 1.16 arc second.

 

  I will use both for polar aligning depending on circumstances of where I set up.

 

  Thanks for making this available to the community.

 

Ron

Ron - Thank you for taking the time to report back on your results, and, you're welcome.

 

I'm glad that you are having some success using QPPA to do your polar alignment.  Congratulations on getting a PoleMaster.  Sounds like you are another satisfied customer.

 

PoleMaster measures star positions to within one pixel of their sensor.  The cursor program I'm using only measures star positions in SCREEN PIXELS.  My camera/telescope combination has a 1.48 x 2.23 degree FOV.  My laptop display is 1366 x 768 pixels.  With the images displayed in the full screen mode in BYEOS each pixel corresponds to 

 

(1.48 x 60) / 768 = 0.116 arcmin / screen pixel.

 

If there is a discrepancy between PoleMaster and my QPPA program I would be inclined to believe the PoleMaster results because it has been tested quite a bit by many astronomers like yourself.

 

I'll be working on a much easier to use version in a few weeks with my son when he visits from Arizona. He is the one who created the Cursor program.

 

All the best,

 

Steve

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Hi Steve

 

  It was my pleasure to help evaluate this and before Polemaster It was making my polar alignment life much more enjoyable.

 

  Another factor which I forgot to mention is that I was using the Atmospheric modeling  available in Polemastrer.  I am located right at 30 north.

 

  Anyway both are close enough with my EQ  mount.  I took my SCT mounted on a wedge out last night.  I only used Polemaster.  The sky was probably 80% covered with clouds but finally a clear opening drifted over the pole area and I got a good alignment.  I really feel that Polemaster was aligned well but not so sure I was close to on the center line of the OTA.  I will play with that some more then see if QPPA plays well with the wedge mounted fork telescope when I get the time and opportunity.  The 10 inch SCT get less playtime since the light pollution and time to set up has come into play.  More on this as it happens.

 

Ron

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Hi Steve

 

  It was my pleasure to help evaluate this and before Polemaster It was making my polar alignment life much more enjoyable.

 

  Another factor which I forgot to mention is that I was using the Atmospheric modeling  available in Polemastrer.  I am located right at 30 north.

 

  Anyway both are close enough with my EQ  mount.  I took my SCT mounted on a wedge out last night.  I only used Polemaster.  The sky was probably 80% covered with clouds but finally a clear opening drifted over the pole area and I got a good alignment.  I really feel that Polemaster was aligned well but not so sure I was close to on the center line of the OTA.  I will play with that some more then see if QPPA plays well with the wedge mounted fork telescope when I get the time and opportunity.  The 10 inch SCT get less playtime since the light pollution and time to set up has come into play.  More on this as it happens.

 

Ron

Ron - A couple of thoughts:

1)  Thanks for the "heads up" on the atmospheric medeling.  I may have to look into that.

2)  Both PoleMaster and QPPA will align your mount's RA axis to the NCP.  Accurately aligning the "center line of the OTA" to the RA axis (the zero position) is normally accomplished with a 1-star alignment after the polar alignment is complete.  However, QPPA and PoleMaster will both still work even though the OTA is not perfectly aligned with the RA axis during the Polar Alignment process.

3)  QPPA won't work with your 10 inch SCT because once you are roughly polar aligned (Polar Scope?) the FOV will be too small to include Polaris which is needed.  PoleMaster still works because it has it's own optics, and, it's FOV is always the same.

 

Clear skies,

 

Steve

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Hi Steve

 

    OK on this.  Currently only Temp, atmospheric pressure are used.  I was expecting humidity too but not used.  I have a Stickstation so I have what i need measured at the telescope location at the time I input it.

 

  On Nr 2 -  What if the Polemaster is skewed just a bit to the right or left of center?  That is my concern.  The Polemaster is mounted on a camera mount with a 90 degree bracket on the OTA but probably is not looking directly ahead.  Could be faceing up, down, left or right a little bit. Not gross amount but set up by eye, maybe in the dark.  In the future I will probably try to line up Polaris in the 10 inch and Polemaster before starting.

 

  On Nr 3 - I am going to probably mount my ST80 piggy back for polar alignment only.  Will have to see if time becomes a factor.  Trying to do things fairly quickly but if aligning twp OTAs and or cameras take a long time then the benefit is lost.

 

  Anhyhow way off topic of BYE.  Again thanks for making this method available.

 

Ron

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Hi Steve

 

    OK on this.  Currently only Temp, atmospheric pressure are used.  I was expecting humidity too but not used.  I have a Stickstation so I have what i need measured at the telescope location at the time I input it.

 

  On Nr 2 -  What if the Polemaster is skewed just a bit to the right or left of center?  That is my concern.  The Polemaster is mounted on a camera mount with a 90 degree bracket on the OTA but probably is not looking directly ahead.  Could be faceing up, down, left or right a little bit. Not gross amount but set up by eye, maybe in the dark.  In the future I will probably try to line up Polaris in the 10 inch and Polemaster before starting.

 

  On Nr 3 - I am going to probably mount my ST80 piggy back for polar alignment only.  Will have to see if time becomes a factor.  Trying to do things fairly quickly but if aligning twp OTAs and or cameras take a long time then the benefit is lost.

 

  Anhyhow way off topic of BYE.  Again thanks for making this method available.

 

Ron

Hi Ron - No need to worry about getting the PoleMaster perfectly aligned.  The alignment process is not affected by misalignments of the PoleMaster.  The alignment accuracy will be unaffected.

 

Good luck with your piggy back setup.

 

Where do you post your AP images?  I'd like to see your work.

 

Steve

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I ran a test tonight with a modified QPPA to include a correction for atmospheric refraction for my Latitude of 37 deg (correction is 0.75 arc min which corresponds to 6 screen pixels for my system).  After the alignment I turned off the Dec guiding and let PHD2 guide (RA only) for 20 min.  At the end of 20 min the Dec had only drifted about 1.5 arc sec.  This corresponds to a PA error of about 0.33 arc min!  

 

Many thanks to Ron for pointing out the Atmospheric Refraction correction.

 

The direction of the atmospheric refraction correction in the image depends on the orientation of the camera.  The magnitude (number of screen pixels) of the atmospheric refraction correction depends on the vertical FOV of the camera and the number of vertical screen pixels.  Because of all these variables I'm afraid adding it to QPPA might be confusing to most users.  I may just leave it in my personal version because I understand all the variables.  Just thinking out loud for now.

 

Steve

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HI Steve

 

  OK thanks I will use a mounting setup and get as close as possible and not worry about it.  On some of the posts several seasoned users point out that at the distance Polaris is from earth you could have the camera positions a 100 miles away as long as it would rotate with the mount in RA the parrallax would not be affected enough to throw the alignment off for most if not all commercial equipment used by Amateur Astronomers.

 

  I don't post any pictures.  Timewise, 95% of my play is under near max light pollution.  The other 5% are under somewhat dark skies but often hampered by clouds.  My interest in Astronomy has been driven by Pictures in the Astronomy Magazines in the 60s, 70 and 80s and telling myself I am going to get pictures like that someday.  With todays technology and am able to get those images.

 

  On the Atmospheric corrections, I fully understand that because I found using the stock QPPA that there was a difference in the orientation of the camera.  It was by accident but there is a difference.  Polemaster tries to keep things in the set up simple by using which side the USB connector is on.

 

  I have enough problems trying to determine the orientation of the camera on the scope and have found one that I use most of the time.  It may or may not be the accepted 'correct' way.  I can't think of a way for you to have a "This side Up" for correct orientation which is also affected by the number of mirrors or no mirrors, as I understand it.

 

  Good luck with your project and thanks for all of the words on the subject.

 

Ron

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Ron,

 

I am not sure that there is such a thing as a correct or incorrect camera orientation for imaging. However, there is a common presentation of final images. For example, you always see the North American Nebula oriented with America above the Gulf of Mexico and the Pelican Nebula to the right. To see it with a different orientation would feel odd.

 

If you have a large enough FOV, you can achieve that presentation regardless of the camera position. That said, I typically maintain the same camera orientation unless I have a reason to change it. That reason is typically a large target, such as M31, where I want to display the disk of the galaxy diagonally in the image. Keeping the same orientation from session to session allow me to combine images from multiple sessions with a minimum of cropping.

 

It has been an interesting discussion between you and Steve about polar alignment. It makes me glad that I use a permanent setup and only even check my PA on an annual basis.  It has been about a year since I last checked my PA but my last imaging target was the Eastern Veil Nebula where I shot 20 minute Ha exposures. I was pleased with the final result so it seems that my PA is still very close.

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This new approach basically works like PoleMaster except that you use your own camera/telescope to capture the images.  In other words, you don't need to purchase any new imager to attach to your mount.  

 

If anyone gives this a try please let me know how it works for you (good or bad).  Every time I've used this approach (takes me less than 10 minutes) I have achieved a PA with better than 1 arc minute accuracy.

 

Steve

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Hello Steve

 

  I have tried your method twice and have not had good results yet.

 

  I looked for similar programs/plans/efforts mostly because my mount, a Meade LXD 75, has a polar alignment scope with the Polaris location etched in 2006 or before.  Now Polaris has moved from the circle according to some articles on polar alignment I have read.  Also I have to set up my mount each time I go out to observe here at the house.

 

  On my first try the spreadsheet gave me a position to move Polaris to position  of  -03 and I forgot the other.  The second time I had a move to position of -30 as one coordinate.  As you know these are off the picture.

 

  I will still try this method several more times since it doesn't take up a lot of time and here at the house I am under terribly polluted skies.  I can spend the time refining my initial setup to get a hopped for result.

 

  I do have several limiting factors.  1)  I have not found a way to turn off either of the  axis motors. 2)   After I set the mount as close as I can I tried using the one star polar align but with the Meade it directs you to center Polaris first to where it believes it to be.  I did that the first time but the second time I left it where the QPPA had set it (or as close as I could get) and accepted that.  My OTA is a SN6 inch f5.  The fl is near 765 mm.

 

  My results  both times was PHD2 indicating the total  RMS error was under 3" except for excursions that are caused by known Periodic Error.

 

  I plan to use a ST80 OTA for a better field of view and possibly a 400 mm camera lens to see if the FOV of the SN6 is a true limiting factor. When I complete my evaluation depends on time and clear sky availability.  Feedback may be a while in coming.

 

  I will continue to use your spreadsheet method until I decide it is useful for me or not.  I will let you know my decision.

 

Ron

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Steve,

 

Can you actually guide with 1 arc-minute of misalignment?

 

It takes me an hour or 2 with PHD2, but I usually get <5 arc-seconds of RMS error. That is close to my seeing limit. With that type of alignment I am able to image with for several months. My last PA was almost a year ago and my most recent imaging effort was 20 minute Ha exposures of the Eastern Veil Nebula. I had no trouble guiding within +/- 1 arc-second.

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Hi Ron - Thanks for giving QPPA a try and for posting your results.

 

I have a few questions if you don't mind:

1)  Did you move the scope in Declination at any time during the alignment?  I don't believe I mentioned it, but, the Dec should NOT be moved at all during the PA calibration.

2)  Was Polaris in your third image, and, did you leave the mount in the third position for the remainder of the PA?

3)  You mentioned "I have not found a way to turn off either of the  axis motors". Does that mean that the RA drive is turned ON?  If the answer is yes, that is what you want.

 

I don't use the hand controller routine to do a 1-star alignment.  After the PA is complete I rotate the RA axis to get to the "zero position" and then turn the mount Off and then On (to reset zero position).  Then I use the GoTo feature to slew to a bright star and then use the Sync feature to correct for any RA/Dec errors.  That completes the alignment.

 

Hope this is of some help.  If this isn't clear please let me know.

 

Steve

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Steve,

 

Can you actually guide with 1 arc-minute of misalignment?

 

It takes me an hour or 2 with PHD2, but I usually get <5 arc-seconds of RMS error. That is close to my seeing limit. With that type of alignment I am able to image with for several months. My last PA was almost a year ago and my most recent imaging effort was 20 minute Ha exposures of the Eastern Veil Nebula. I had no trouble guiding within +/- 1 arc-second.

Hi Rick - Sorry for any confusion.  When I say 1 arc-minute of misalignment I'm referring to the misalignment between where the mount RA axis is pointing and the North Celestial Pole (NCP).  I'm not referring to the guiding accuracy which is displayed on the PHD2 graph.

 

Sounds like you have a very good polar alignment.

 

Steve

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OK, and what I am saying is how many arc-seconds of declination drift have been measured by PHD since the start of the drift run. This is measured by drawing a best fit line through the plot of all the dec errors that have occurred during the drift run.

 

So I guess that the answer to my question is yes, your autoguiding can correct for drift due to a polar misalignment of 1 arc-minute. Perhaps I am being unnecessarily precise in my alignment. Still, I guess that closer is better.

 

Thanks for sharing.

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Hi Rick

 

  Yes be thankful you have a permanent setup.

 

    I tried to find an answer to "Which way is up?".  In the end I decided it wasn't that big of a concern since what I do is for me primarily.  With all of the mirrors rather than be confused I live in bliss.

 

  The atmospheric modeling seemingly has to have a specific camera orientation to be effective.  Something I dont understand but accept.

 

  I do send a few things to others who follow my adventures but mostly because they don't have the time, money or patience to do astronomy on their on.  When people walk by when I am out they come over and talk about what I am doing.  Very close to the beginning is the phrase "I watch the astronomy programs on PBS."  So their interest is at a level that doesn't warrant expending any of the above.

 

  I tried it with my Meade LX200R the other night and will again the next time I go out.  II use the LX200R mostly in Alt-Az because of the time it takes me to get PA and not necessarily good PA.  If I can get a good, just good PA, I will take it out more often when the right targets are out there.  I feel I need to be satisfied with a setup in under 30 minutes other wise I will use the LXD75 SN 6  because the set up time meets that.

 

  I have the standard  line filters and have used them but as you know the exposures are quite long.  I know from the descriptions on some images posted the people spend a week or two getting the data to their satisfaction.

 

  The Veil(s) are in the light dome of a major city now and Orion is behind trees on the other side.  I know if I used the line filters with the mono imager I could press on but I don't.

 

  M45 and M45 have my attention for now.

 

  For M31 from time to time I use my Canon 100-400 set to aroiund 300 mm and get a pretty good representation. 

 

  Hope you have clear skies for the winter DSO as they approach and pass.

 

Ron

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OK, and what I am saying is how many arc-seconds of declination drift have been measured by PHD since the start of the drift run. This is measured by drawing a best fit line through the plot of all the dec errors that have occurred during the drift run.

 

So I guess that the answer to my question is yes, your autoguiding can correct for drift due to a polar misalignment of 1 arc-minute. Perhaps I am being unnecessarily precise in my alignment. Still, I guess that closer is better.

 

Thanks for sharing.

You are right Rick, closer is definitely better.  Your alignment to within 5 arc-seconds is extremely good.  I'm very impressed.

 

The new PoleMaster that is so popular only promises to get to within 30 arc-seconds, but, it seems to be good enough for everyone so far.

 

The biggest problem with too large a misalignment will be image rotation for long exposures.  The guide system will correct for the slow Dec drift, but, it won't correct for the image rotation which, of course, leads to star tails.

 

Thanks for your responses.

 

Steve

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Hello Steve

 

  I have tried your method twice and have not had good results yet.

 

  I looked for similar programs/plans/efforts mostly because my mount, a Meade LXD 75, has a polar alignment scope with the Polaris location etched in 2006 or before.  Now Polaris has moved from the circle according to some articles on polar alignment I have read.  Also I have to set up my mount each time I go out to observe here at the house.

 

  On my first try the spreadsheet gave me a position to move Polaris to position  of  -03 and I forgot the other.  The second time I had a move to position of -30 as one coordinate.  As you know these are off the picture.

 

  I will still try this method several more times since it doesn't take up a lot of time and here at the house I am under terribly polluted skies.  I can spend the time refining my initial setup to get a hopped for result.

 

  I do have several limiting factors.  1)  I have not found a way to turn off either of the  axis motors. 2)   After I set the mount as close as I can I tried using the one star polar align but with the Meade it directs you to center Polaris first to where it believes it to be.  I did that the first time but the second time I left it where the QPPA had set it (or as close as I could get) and accepted that.  My OTA is a SN6 inch f5.  The fl is near 765 mm.

 

  My results  both times was PHD2 indicating the total  RMS error was under 3" except for excursions that are caused by known Periodic Error.

 

  I plan to use a ST80 OTA for a better field of view and possibly a 400 mm camera lens to see if the FOV of the SN6 is a true limiting factor. When I complete my evaluation depends on time and clear sky availability.  Feedback may be a while in coming.

 

  I will continue to use your spreadsheet method until I decide it is useful for me or not.  I will let you know my decision.

 

Ron

Ron - I think I know the problem.   Sometimes Excel won't recalculate all cells after you update cell data. 

 

After entering the Polaris Position in Frame/Focus information, then, left-click in cell P26 (or any other cell to the bottom right of the green results boxes).  This will cause the spreadsheet to calculate the final results in the green boxes.  I believe this will solve your problem.

 

Thanks for your perseverance.

 

Steve

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