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Jeff2011
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Celestron VX Mount Tracking Test
      #5783567 - 04/07/13 11:12 AM

I have only had my VX mount for just over a week now and am still learning how to use it. During the second night out with it, I decided to test how well it tracked unguided. Here were my procedures for aligning before my test.

1. Polar align on Polaris with reticle eyepiece
2. 2 star alignment + 3 calibration stars
3. Polar alignment via hand controller polar align function
4. 2 star realignment + 3 calibration stars

I then barlowed my reticle eyepiece (12.5mm ep + 2x barlow) and tracked a star for 15 minutes. Did this on two stars on either side of the meridian. The double crosshair lines of the EP make a small box at the center and after 15 minutes the star moved from the center of that box to the edge of the box. This was a very smal movement.

I then decided to break out the DSLR to see how long an exposure I could take before getting star trails. The DSLR was mounted to my Astro Tech 72ED with a focal length of 430mm. I was able to get a 2 minute shot with round stars. However 3 minutes resulted in some star trails.

I was very pleased with these results.

Is this pretty much the upper limit of what I can expect without guiding, or should I be able to do better?

Is the polar alignment function of the hand controller going to give me as good a results as a star drift alignment?


Jeff


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Raginar
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5783608 - 04/07/13 11:37 AM

Jeff,

Nothing will beat a drift alignment. The software gets you close but it's based on an imperfect model. A drift alignment is based on observation.


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budman1961
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Re: Celestron VX Mount Tracking Test new [Re: Raginar]
      #5783651 - 04/07/13 12:00 PM

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy


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Whichwayisnorth
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Re: Celestron VX Mount Tracking Test new [Re: budman1961]
      #5783874 - 04/07/13 02:04 PM Attachment (108 downloads)

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.

Edited by Whichwayisnorth (04/07/13 02:12 PM)


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Whichwayisnorth
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Re: Celestron VX Mount Tracking Test new [Re: Whichwayisnorth]
      #5783877 - 04/07/13 02:04 PM Attachment (90 downloads)

Here is a zoom in on one star towards the inside of the photo.

Edited by Whichwayisnorth (04/07/13 02:10 PM)


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Whichwayisnorth
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Re: Celestron VX Mount Tracking Test new [Re: Whichwayisnorth]
      #5783886 - 04/07/13 02:11 PM Attachment (64 downloads)

here is one towards the outside of the photo.

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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: Raginar]
      #5783994 - 04/07/13 03:02 PM

Quote:

Jeff,

Nothing will beat a drift alignment. The software gets you close but it's based on an imperfect model. A drift alignment is based on observation.




That is what I was thinking too. Just wanted to get another opinion. I am no stranger to star drift alignments since I have done it on my EQ platform many times. Since my light polluted skies limit my exposure time the mount polar alignment appears to be acceptable for the focal length I am using. Might try a star drift next time just to experience it with the mount. Thanks


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: budman1961]
      #5784001 - 04/07/13 03:05 PM

Quote:

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy




Andy, the manual recommends realigning and calibrating after a hand controller polar alignment.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: Whichwayisnorth]
      #5784016 - 04/07/13 03:09 PM

Quote:

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.




Thanks for posting your results. Your focal length is much longer than mine even with the reducer. That probably explains why I am getting 120 seconds with no trailing to your 90.


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Whichwayisnorth
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5784045 - 04/07/13 03:20 PM

Quote:

Quote:

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.




Thanks for posting your results. Your focal length is much longer than mine even with the reducer. That probably explains why I am getting 120 seconds with no trailing to your 90.




Correct. When I was using my reduced to f/4 80mm refractor I could go well over 3 minutes unguided. In fact at one point I had it so dialed in I got 17 minutes of drift aligning and the star never moved from center.


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budman1961
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Re: Celestron VX Mount Tracking Test new [Re: Whichwayisnorth]
      #5784282 - 04/07/13 04:45 PM

Jeff and Michael,

After you finish the polar alignment, to you power off the mount and then do the 2 star and 4 calibration stars? Ive seen somewhere that people do this also. What fo you all do?

Andy


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: budman1961]
      #5784304 - 04/07/13 04:56 PM

After the polar align, I do not power off the mount. I slew to a star, press align and replace one of the previous aligned or calibrated stars.

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Whichwayisnorth
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5784335 - 04/07/13 05:11 PM

No I don't. I just move on with the night. Go-to's are spot on and there is no drift. I wasn't aware I was being encouraged to do any further syncing or replacing alignment stars. I guess it couldn't hurt. Perhaps next time.

FYI, I typically connect using The Sky X. I have t-point so I spend about 20 minutes doing some sky modeling to get my go-tos perfect. When I am done for the night I hibernate the scope and save my t-point model.


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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5784506 - 04/07/13 06:40 PM

Quote:

Quote:

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy




Andy, the manual recommends realigning and calibrating after a hand controller polar alignment.




Not for the later releases of the firmware. With these, realignment isn't necessary.


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Kendahl
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5784815 - 04/07/13 09:19 PM

Were you using periodic error correction? If not, that should help significantly.

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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5785504 - 04/08/13 09:29 AM

Quote:


Not for the later releases of the firmware. With these, realignment isn't necessary.




Thanks Dave. I will check my firmware version and see if it is out of date.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: Kendahl]
      #5785518 - 04/08/13 09:36 AM

Quote:

Were you using periodic error correction? If not, that should help significantly.




Nope. Don't have an autoguider yet. According to the manual (sorry that is all I have to go by right now), PEC requires an autoguider to get it configured. Please correct me if I am wrong. This is my first GEM.

I have been eyeballing the QHY5L II Mono. Others have suggested that over the Orion Autoguider.

Right now I am trying to see what I can get with unguided shots. Unfortunately the clouds have prevented me from doing that. It cleared off last night so I tried to set up. Was able to site in on Polaris and by the time I got to my second alignment star, the clouds rolled back in. Bummer.


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zawijava
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5785522 - 04/08/13 09:39 AM

Could someone post a link to the AVX Firmware updates. I checked out the Celestron Support but didn't see anything [specifically] for the AVX thanks, Tim

Quote:

Quote:


Not for the later releases of the firmware. With these, realignment isn't necessary.




Thanks Dave. I will check my firmware version and see if it is out of date.




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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: zawijava]
      #5785548 - 04/08/13 09:57 AM

Tim,

I didn't see anything either. Is the manual then out of date regarding realinging after a hand controler polar alignment?


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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5785556 - 04/08/13 10:04 AM

Quote:

Tim,

I didn't see anything either. Is the manual then out of date regarding realinging after a hand controler polar alignment?




I'm going to venture a guess that you are correct. Somebody just did a copy/paste of that section of the manual from the CG5. The CGEM/CGEM DX/CGE/CGE Pro firmware updates eliminated the requirement of shutting off the mount and realigning after the ASPA routine was done. I've always kept my Celestron mounts at the current firmware levels. My plan is to pick up an AVX at NEAF weekend after next. Celestron has not been good, at all, about keeping the manuals up-to-date after firmware revisions. That's been the case for years now.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5785706 - 04/08/13 11:21 AM

Thanks Dave.

That is why I look at manuals with a grain of salt. I am in the software development business myself so I know how it goes with documentation. I am just glad to be able to tap into the knowledge and experience of CN members like yourself.


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cn register 5
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5786139 - 04/08/13 02:23 PM

I've just looked at the AVX manual. Page 30.

It doesn't say anything about cycling the power. It says that it is a good idea to check the alignment and talks about replacing alignment and calibration stars but doesn't say that you have to.

Anyway you don't have to cycle the power or do a relignment. Checking a goto is a good idea but you should do it before doing the polar alignment as well as afterwards.

My opinion is not to bother with a polar finder but get a reticle EP. I use a simple home made one

And treat CN with a pinch of salt, not everyone distinguishes opinion or speculation from fact. I've seen a lot of statements made with total confidence that I know to be wrong.

Chris


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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5786272 - 04/08/13 03:56 PM

Quote:

And treat CN with a pinch of salt, not everyone distinguishes opinion or speculation from fact. I've seen a lot of statements made with total confidence that I know to be wrong.




Man, you have THAT right! Take a look at some advice here that a member gave: link.

Edited by DaveJ (04/08/13 03:57 PM)


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5786314 - 04/08/13 04:13 PM

Quote:

After the polar align, I do not power off the mount. I slew to a star, press align and replace one of the previous aligned or calibrated stars.





Chris,

The above is from one of my previous replies in this post. I do not power the mount off, but I did follow their recommendations on replacing the alignment and calibration stars after a hand controler polar alignment.

I read through Dave's response too fast and missed the power off part. I am assuming that the power off recommendation came from the CG5 manual. So then Celestron must have updated the AVX document.

Anyways. Hope I did not start a war here .

Edited by Jeff2011 (04/08/13 04:21 PM)


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cn register 5
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5786509 - 04/08/13 05:53 PM

This realign myth seems to come from previous polar align methods and methods for other mounts where the alignment is not preserved. I don't know about the original CG5 because I never tried it but it could well be true for that one.

That was 5 years ago or more and the software has moved on - at least the Celestron software has.

Once you have an alignment matrix it is quite easy to apply the altitude and azimuth rotations to that matrix to transpose it to a new coordinate system.

Of course if you have done a poor alignment in the first place then the intial gots and correction error will be poor. After a "polar alignment" not only will your polar alignment be bad but your gotos will still be bad. Garbage in garbage out.

And the mount gets blamed.

In my opinion if you don't use a reticle EP you can forget about precision, in gotos or polar alignment.

Chris


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5786683 - 04/08/13 07:25 PM

Quote:

In my opinion if you don't use a reticle EP you can forget about precision, in gotos or polar alignment.
Chris




I don't own a polar finder scope partly because my mount did not come with one and partly because many CN members like Chris do not think highly of them. A reticle EP is a must have. However, I would like to delve deeper in the polar alignment procedure itself. In my step one, I did an initial polar align on Polaris by centering Polaris in my reticle EP using the Alt/Az adjutments of the GEM. Since Polaris is approximately 0.7 degress from the NCP, my initial alignment was off. This was later corrected when I did a polar alignment using the mount software. This involved centering on a Star near the Meridian but not near the pole. Then executing the polar align function on the hand control which moved away from the star and then moves back but not exactly on the star. Then I centered the star in the reticle EP using the Alt/Az adjustments on the mount. Using the software polar align, the reticle EP is required for accuracy, but on the rough polar align that I did in step 1, the reticle is not. I am planning on changing step one as follows:

Dial in Polaris in Sky Safari and turn on the NCP marker and create a ring with crosshairs the size of 1.5 degrees. Place the center of the crosshairs on the NCP and see where Polaris falls. Of cource I will need to have Sky Safri flip the view horizontally to match the view through my refractor. I will then take an eyepiece that gets a 1.5 true field of view and place Polaris using the Alt/Az adjustments of the mount in the same place as that I see it in Sky Safari. If I then really wanted to get an accurate polar alignment, I could then skip the software Polar alignment in my step 3 and just do a star drift alignment from there using the reticle EP. If the clouds permit, I will try this tonight.

I remember reading that a polar alignment should only be as accurate as it needs to be. So if I am just trying to take 2 minute exposures, then my initial method will work just fine. If I need longer, then it looks like I will need to do a star drift alignment.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5788330 - 04/09/13 02:38 PM

My main objection to the polar finder is that I'd have to demolish my house to use it

It may also be more difficult to use for us in the UK because Polaris is much higher than for most of the USA.

With ASPA it seems better to me to spend the money on a reticle EP, I think it will give a better quality alignment and this will help with ASPA.

Chris


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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5788623 - 04/09/13 04:23 PM

Quote:

With ASPA it seems better to me to spend the money on a reticle EP, I think it will give a better quality alignment and this will help with ASPA.




Hi Chris,

Truer words have never been spoken. That's exactly how I feel about ASPA, reticle EPs and polar alignment scopes in general. ASPA just plain works for me, and has since the first time I tried it.


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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5789001 - 04/09/13 07:38 PM

Chris,

This was corrected around firmware version 4.2 that you no longer needed to re-align after you did ASPA. Prior to that, it was a requirement for, at the very least, CGEMs.

Hope that clarifies that little issue. I was still doing it until I got rid of my CGEM because that was my habit routine from when I first got it.

Sometimes we all to be right when we should just ask if it matters


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Re: Celestron VX Mount Tracking Test new [Re: Raginar]
      #5791107 - 04/10/13 07:27 PM

Strange, none of the beta versions needed this.

Chris


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Raginar
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5791232 - 04/10/13 08:21 PM

Beta versions from 2010? It was a common thing to do up until v4.2.

Chris


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Re: Celestron VX Mount Tracking Test new [Re: Raginar]
      #5791762 - 04/11/13 04:13 AM

I was testing this in 2006/7 and a realign after doing the polar align was never essential. This is what the developer told us. I tried it and it was correct. I can't speak for the manual, we didn't have one, just the instructions in the HC.

Yes, a lot of people thought a realign was essential. They were wrong. It would have taken them a few seconds to check this, all they needed to do was a goto after doing the ASPA and see what they got.

Chris


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freestar8n
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5791770 - 04/11/13 04:34 AM

I think there may be some confusion of unsyncing with recalibrating - after polar align. The first step in ASPA is to sync on the star - and that star is still sync'd after the alignment completes. Any time you sync on a star you improve pointing at that star - but may lose accuracy far away from that star. So it may or may not be desirable to unsync after ASPA - depending on how far away you intend to wander, and how bad the pointing is.

My recommendation - based on experience with cge and cge-pro - plus the basic principles of ASPA is:

1) Start with a good 2+4 alignment so the mount is calibrated

2) Use a star near the meridian and maybe 30 degrees above the horizon - i.e. ignore the equator here - you want a star lowish in the sky and opposite the pole. This may differ from the manual.

3) Don't spend too much time fiddling with the alt/az motion to center the star - just do one move in az and one in alt.

4) When ASPA completes, check the accuracy in an area of sky you want to study. If pointing is a bit off, first try unsync to see if it improves

5) If it is still a bit off and you want to improve it, replace the two alignment stars with the same ones, or new ones.

That should be all you need to do, and you definitely shouldn't power down. Unsyncing is simple and may improve pointing.

The main thing is - after ASPA everything may be fine and you don't have to do anything more, but if you want to improve it, there are two simple things to try.

Frank


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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5791995 - 04/11/13 09:30 AM

Quote:

I was testing this in 2006/7 and a realign after doing the polar align was never essential. This is what the developer told us. I tried it and it was correct. I can't speak for the manual, we didn't have one, just the instructions in the HC. Yes, a lot of people thought a realign was essential. They were wrong. It would have taken them a few seconds to check this, all they needed to do was a goto after doing the ASPA and see what they got.




I'm in complete agreement with Chris on this. I, too, have been using this exact same technique from day one with ASPA with success. I even told the Celestron reps how the ASPA worked following its installation in my CGE prior to NEAF that year. They, quite frankly, were baffled by it all and were explaining its function in a most bizarre (and incorrect) way to some potential customers.


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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792055 - 04/11/13 10:21 AM

The need for realignment will depend on how far off you original polar alignment was before doing aspa. Do a test yourself and you will see an increase in pointing accuracy. The need of a realignment or lackthereof has been discussed on teamcelestron.com. If you objects are landing on you camera chip with the same accuracy as before the aspa your fine. If not redo the alignment. It only takes a few minutes and could save some frustration.

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DaveJ
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Re: Celestron VX Mount Tracking Test new [Re: Stew57]
      #5792242 - 04/11/13 12:16 PM

Quote:

The need for realignment will depend on how far off you original polar alignment was before doing aspa. Do a test yourself and you will see an increase in pointing accuracy. The need of a realignment or lackthereof has been discussed on teamcelestron.com. If you objects are landing on you camera chip with the same accuracy as before the aspa your fine. If not redo the alignment. It only takes a few minutes and could save some frustration.




Oh, I HAVE done the test - a zillion times. I never pushed it to see how far off I had to be to get it NOT to work, but I've intentionally misaligned from the pole by at least 5 degrees, did the 2+4 alignment using an illuminated cross-hair reticle eyepiece, selected a star near the intersection of the meridian and celestial equator, performed the ASPA using that star, and went about my business with every object - either side of the meridian - falling dead center. Once centered, I could leave the object with no drift whatsoever from the center of a high-powered eyepiece for as long as I chose. In other words, pretty darned perfect behavior with both goto centering and subsequent tracking. That's what has worked for me. I've never performed another alignment following ASPA. HOWEVER, the 2+4 with cross-hair reticle is required FIRST before the ASPA so the firmware has an accurate model of the sky. The ASPA uses that model to perform its task. Any discrepancy between what I've explained and what was actually done by the user will result in an inaccurate internal model and render ASPA far less accurate and probably require another alignment. Hey, it works perfectly for me - what can I say? Math is doing the magic and if the rules are followed, it'll do it every time.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: Stew57]
      #5792252 - 04/11/13 12:19 PM

My interpretation of their recomendation in the manual to resync after the ASPA was in case your scope shifted while making the Alt/Az adjustment. I assume they did not want people to call them up and whine about ASPA not working. I think if you are careful when making the Alt/Az adjustment and have your scope attached tightly to the mount, the resync of the alignment stars is not needed after the ASPA.

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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792337 - 04/11/13 01:06 PM

My experience is a bit different. I use a mallincam in my C11 with cross box enabled (more accurate than a reticular eyepiece), do a 2+4 alignment followed by an aspa. If the mount needs little adjustment the objects will fall on the chip at F10. If the mount needs much adjustment then the objects will no longer fall on the chip. If I redo the 2+4 they again start falling on the chip. Derik from celestron acknowledges that sometimes an alignment will need to be redone. If your objects are landing where you want them, go with it, if not a redo is in order. BTW how long an object stays in an eyepiece has nothing to do with pointing accuracy but it does speak to polar alignment. I had one CGEM that would keep the object in the eyepiece all night with a couple of arc minutes of PE. The object just oscillated back and forth roughly centered all night. Was not a factor (you couldn.t tell) visually but for use with the mallincam it was a disaster.

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Re: Celestron VX Mount Tracking Test new [Re: Stew57]
      #5792375 - 04/11/13 01:24 PM

Quote:

BTW how long an object stays in an eyepiece has nothing to do with pointing accuracy but it does speak to polar alignment.




Hi Stew57, I'm fully aware of that - but it's a common mistake I've seen made here on the forum. There's a gigantic difference between a goto alignment and a polar alignment. A mount can be set up to have neither, one or both. Both is, of course, preferred. I've been setting up GEMs for fifty-three years and know the difference.


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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792392 - 04/11/13 01:34 PM

Quote:

Quote:

BTW how long an object stays in an eyepiece has nothing to do with pointing accuracy but it does speak to polar alignment.




Hi Stew57, I'm fully aware of that - but it's a common mistake I've seen made here on the forum. There's a gigantic difference between a goto alignment and a polar alignment. A mount can be set up to have neither, one or both. Both is, of course, preferred. I've been setting up GEMs for fifty-three years and know the difference.




BUT in the context of ASPA, the polar alignment is dependent on the goto alignment - and thus, the tracking is also. A weak goto alignment will result in a weak polar alignment - and poor tracking.


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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792419 - 04/11/13 01:48 PM

Quote:

Any discrepancy between what I've explained and what was actually done by the user will result in an inaccurate internal model and render ASPA far less accurate and probably require another alignment. Hey, it works perfectly for me - what can I say? Math is doing the magic and if the rules are followed, it'll do it every time.




At your latitude using the equator may work ok but it is probably not optimal, and it would work worse for people closer to the equator. So again I would use a star lower in the sky to improve the azimuth alignment accuracy.

Also - people are talking about realignment after ASPA to improve accuracy. There is another thing to try, which is just unsyncing. Syncing is usually only good for a part of the sky, and since the mount is still sync'd after ASPA, it may lead to inaccurate goto's across the sky. It may also be fine - but the point is there is something else to try and it is faster than realignment.

Frank


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Re: Celestron VX Mount Tracking Test new [Re: freestar8n]
      #5792440 - 04/11/13 02:01 PM

Quote:

There is another thing to try, which is just unsyncing. Syncing is usually only good for a part of the sky, and since the mount is still sync'd after ASPA, it may lead to inaccurate goto's across the sky. It may also be fine - but the point is there is something else to try and it is faster than realignment.




The unsyncing is part of the ASPA, assuming the ASPA is done correctly. I left that part out thinking the reader would know that it's included as part of the ASPA. That's the only way to get dead-centered gotos on both sides of the meridian following ASPA.


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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792487 - 04/11/13 02:19 PM

Unfortunately there are now many documents on ASPA and I don't know what is official. But I would not consider unsyncing "part of" ASPA because you would NOT want to unsync if you intend to observe near the star you used for ASPA. You are only prompted to unsync if you choose to start a new alignment. My point is - you can unsync without doing a new alignment - and it may improve all sky pointing.

I'm pretty sure many people don't realize this is a step that could help them - and avoid the need for realignment. It's something easy to try anyway.

I don't know of any celestron document that has corrected the mistaken notion that the equator is somehow optimal - but I hope people can realize it from common sense - e.g. by realizing it would fail completely for someone near the Earth's equator since such a star would be nearly overhead.

Frank


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Re: Celestron VX Mount Tracking Test new [Re: freestar8n]
      #5792557 - 04/11/13 02:51 PM

Quote:

I don't know of any celestron document that has corrected the mistaken notion that the equator is somehow optimal - but I hope people can realize it from common sense - e.g. by realizing it would fail completely for someone near the Earth's equator since such a star would be nearly overhead.




You are, obviously, exactly correct. I'm at 41° 11" latitude so the intersection of the celestial equator and meridian is 48° 49" in altitude due south so the AZ adjustment is still effective. I'll admit that the recommendation in the manual to use a star as close to the celestial equator & meridian has overly influenced me to the point of being an obsession. I can't see any reason to not follow your advice and use a star closer to the horizon and intersecting the meridian. It would seem that the AZ and the ALT adjustments would have their highest sensitivity there - which is exactly what we're after. For those that are confused by this discussion, imagine you're located at the equator. A star at the intersection of the celestial equator and meridian would be directly overhead. Thus, the AZ manual controls would be totally worthless since you could turn and turn and turn until you're blue and the star would remain centered. Not so if the star is much closer to your local horizon where the AZ manual control has its greatest effect per adjustment.


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Re: Celestron VX Mount Tracking Test new [Re: DaveJ]
      #5792584 - 04/11/13 03:10 PM

Quote:

I can't see any reason to not follow your advice and use a star closer to the horizon and intersecting the meridian.




Thanks - please help spread the word. I think ASPA will work very well for most people as long as the star is not too high in the sky and it is near the meridian. Many of these threads focus on fine details to finesse the results - but there are people who talk of it not working as well as they hoped - and I think using a star lower down may help.

And that will help both the polar alignment accuracy and the GoTo accuracy - since GoTo after ASPA assumes the mount is perfectly polar aligned.

Frank

[edited for clarity]

Edited by freestar8n (04/11/13 03:48 PM)


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Re: Celestron VX Mount Tracking Test new [Re: Raginar]
      #5792585 - 04/11/13 03:11 PM

Quote:

Nothing will beat a drift alignment. The software gets you close but it's based on an imperfect model. A drift alignment is based on observation.




Hmmm...that has not been my experience. When comparing image drift from subframe to subframe, ASPA has always done a better job of controlling it than any drift alignment I could do. I would typically do 5 minute observations without drift before changing the axis, then work on it in the other direction until I could go 5 minutes, and then recheck the first axis, etc. That was typically at high power.

As John mentioned, the key is to do a good goto alignment first, and then do the ASPA. Without a good goto alignment the hand controller model may not be accurate enough. I know that by the time I do a 2+2 or a 2+3 alignment, the controller is putting objects dead center in the eyepiece.

That's when you want to do ASPA. So, I am a believer that it's more accurate than I can be with a manual drift alignment, and it's certainly a lot faster.

Patrick

Edited by Patrick (04/11/13 09:29 PM)


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Re: Celestron VX Mount Tracking Test new [Re: Patrick]
      #5794064 - 04/12/13 10:04 AM

Had the mount out again last night and decided to give ASPA another try. When I do my alignments I use a 12.5mm reticle eyepiece with a 2x barlow. I noticed after the polar alignment, the calibration stars were gone. By gone, I mean that when I went to recalibrate a star after the polar align, there were none to replace. All four calibraton slots that I had filled before the polar align were now open. This is what I saw last week, but I wanted to repeat the test to make sure. After dinking around with it for over two hours, basically repeating the ASPA serveral times to make sure it was working well I decided to take a few shots. Out of 9 frames that were 90 seconds each, 4 had well rounded stars and 5 had slightly oval stars. I did mave the mirror lockup set for the DSLR to prevent vibration from the camera shutter. Not sure if the slightly rounded stars were caused by periodic error or some other cause. It was not windy and the scope was well balanced. Are my results typical for unguided shots?

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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5794167 - 04/12/13 10:53 AM

Quote:

Had the mount out again last night and decided to give ASPA another try. When I do my alignments I use a 12.5mm reticle eyepiece with a 2x barlow. I noticed after the polar alignment, the calibration stars were gone. By gone, I mean that when I went to recalibrate a star after the polar align, there were none to replace. All four calibraton slots that I had filled before the polar align were now open. This is what I saw last week, but I wanted to repeat the test to make sure. After dinking around with it for over two hours, basically repeating the ASPA serveral times to make sure it was working well I decided to take a few shots. Out of 9 frames that were 90 seconds each, 4 had well rounded stars and 5 had slightly oval stars. I did mave the mirror lockup set for the DSLR to prevent vibration from the camera shutter. Not sure if the slightly rounded stars were caused by periodic error or some other cause. It was not windy and the scope was well balanced. Are my results typical for unguided shots?




At what focal length?


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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5794294 - 04/12/13 11:57 AM

Quote:



In my opinion if you don't use a reticle EP you can forget about precision, in gotos or polar alignment.

Chris




Or a camera with a really nice 10x lossless crop mode and centering lines on the display. No eyepiece would ever give you a 10x magnification and still allow you to see the stars. However, certain cameras can do that easily.

There is also the added bonus that you won't have to align with something other than what you are actually using for observing/imaging.


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Re: Celestron VX Mount Tracking Test new [Re: Whichwayisnorth]
      #5794306 - 04/12/13 12:02 PM


Quote:

At what focal length?




430mm


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5794469 - 04/12/13 01:31 PM

Did you "unsync" after ASPA? I haven't yet had the opportunity to run ASPA on my AVX due to bad weather but from what I've read this is a critical piece...I'm just not sure if the ASPA routine prompts you to unsync after polar alignment or if you need to remember to do it??? -Tim

Quote:

Had the mount out again last night and decided to give ASPA another try. When I do my alignments I use a 12.5mm reticle eyepiece with a 2x barlow. I noticed after the polar alignment, the calibration stars were gone. By gone, I mean that when I went to recalibrate a star after the polar align, there were none to replace. All four calibraton slots that I had filled before the polar align were now open. This is what I saw last week, but I wanted to repeat the test to make sure. After dinking around with it for over two hours, basically repeating the ASPA serveral times to make sure it was working well I decided to take a few shots. Out of 9 frames that were 90 seconds each, 4 had well rounded stars and 5 had slightly oval stars. I did mave the mirror lockup set for the DSLR to prevent vibration from the camera shutter. Not sure if the slightly rounded stars were caused by periodic error or some other cause. It was not windy and the scope was well balanced. Are my results typical for unguided shots?




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Re: Celestron VX Mount Tracking Test new [Re: zawijava]
      #5794662 - 04/12/13 02:34 PM

Quote:

Did you "unsync" after ASPA? I haven't yet had the opportunity to run ASPA on my AVX due to bad weather but from what I've read this is a critical piece...I'm just not sure if the ASPA routine prompts you to unsync after polar alignment or if you need to remember to do it??? -Tim





No. It just says it is done and does not prompt for anything else. I then go to replace a calibrated star and all calibrated slots are empty when I try to replace one. It is like an ASAP clears all of them. The previous alignment stars however are still there when I go to replace them.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5794849 - 04/12/13 04:25 PM

On page 30 of my AVX Manual under the heading "Updating your Star Alignment", directly following the ASPA routine it states: "Since the Polar Alignment process requires you to "Sync" the telescope on a bright star before you begin, it will be necessary to undo the sync before realigning". I would guess that since Sync is only helpful within a small area of the sync'ed star that if you DON'T unsync after ASPA then things won't be accurate as you move on to other areas of the sky. -Tim

Quote:

Quote:

Did you "unsync" after ASPA? I haven't yet had the opportunity to run ASPA on my AVX due to bad weather but from what I've read this is a critical piece...I'm just not sure if the ASPA routine prompts you to unsync after polar alignment or if you need to remember to do it??? -Tim





No. It just says it is done and does not prompt for anything else. I then go to replace a calibrated star and all calibrated slots are empty when I try to replace one. It is like an ASAP clears all of them. The previous alignment stars however are still there when I go to replace them.




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Re: Celestron VX Mount Tracking Test new [Re: zawijava]
      #5794990 - 04/12/13 05:30 PM

I guess I don't understand the need for the unsync. If I replace an alignment star with another, does that not imply an unsync of the star being replaced?

I did find out one interesting thing last night. If after an ASPA, I just do the calibration stars again without first replacing the alignment stars, the mount was way off when slewing to a target. It then would not let me replace an alignment star and I had to reboot the mount and start over. Did not try the unsync. Perhaps that is what the unsync command is for. If you get it so screwed up that you can't replace an alignment star anymore.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795039 - 04/12/13 05:41 PM

My understanding is that Sync is a way to make goto's within a small area of the sky more accurate and ANY time you sync you should unsync prior to leaving that area and slewing to another area of the sky. For the time it takes to "unsync" after ASPA it's likely worth the added key strokes. -Tim

Quote:

I guess I don't understand the need for the unsync. If I replace an alignment star with another, does that not imply an unsync of the star being replaced?

I did find out one interesting thing last night. If after an ASPA, I just do the calibration stars again without first replacing the alignment stars, the mount was way off when slewing to a target. It then would not let me replace an alignment star and I had to reboot the mount and start over. Did not try the unsync. Perhaps that is what the unsync command is for. If you get it so screwed up that you can't replace an alignment star anymore.




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Re: Celestron VX Mount Tracking Test new [Re: zawijava]
      #5795223 - 04/12/13 07:01 PM

I am making the assumption that a synced star is one of the two alignment stars. Is that correct or is a sync something different?

What about the calibration stars? Do I need to recalibrate after changing the alignment stars? Do I need to recalibrate after a ASPA?

Thought I had this down. The more I think about it the more I confuse myself.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795264 - 04/12/13 07:27 PM

I believe that AFTER doing the ASPA the only star that you've Synced on is the one used for the Polar Alignment. The alignment you did prior to the ASPA should not contain any Synced stars. After unsyncing from the ASPA star you can then recheck and/or redo your alignment and calibration stars. And from what I've read in this Thread, using a cross-hair centering eyepiece makes everything more accurate. I just picked one up on AM today and looking forward to using it. IMHO the "Sync" option causes more problems than not, possibly because users don't really understand it's shortcomings. -Tim

Quote:

I am making the assumption that a synced star is one of the two alignment stars. Is that correct or is a sync something different?

What about the calibration stars? Do I need to recalibrate after changing the alignment stars? Do I need to recalibrate after a ASPA?

Thought I had this down. The more I think about it the more I confuse myself.




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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795275 - 04/12/13 07:33 PM

AIUI Sync is an offset in Ra and Dec that's applied to the position calculated from the mount model. You can sync on anything and it is independent of the align or calib stars.

There's no need to redo any calibration stars after sync.

Chris


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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5795289 - 04/12/13 07:46 PM

But....what I understand from this Thread and the AVX Manual, if you do not unsync prior to slewing to another part of the sky, then your initial alignment and calibration, as good as they might have been, will likely be [much] less accurate and will get worse the further away from the "synced" star you go. Hence the requirement that you unsync. I believe Users are misunderstanding and misusing the "Sync" option. -Tim

Quote:

AIUI Sync is an offset in Ra and Dec that's applied to the position calculated from the mount model. You can sync on anything and it is independent of the align or calib stars.

There's no need to redo any calibration stars after sync.

Chris




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Re: Celestron VX Mount Tracking Test new [Re: zawijava]
      #5795330 - 04/12/13 08:26 PM

Tim,

Thank you very much for clarifying this. It makes sense to me again. Hopefully it will stay that way.

I can also say that I have seen the behavior you describe. The further away I slewed from the synced star used for ASPA, the less accurate it was.

Edited by Jeff2011 (04/12/13 08:32 PM)


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795477 - 04/12/13 10:05 PM

Glad I could help....due to the weather here in the Northeast for the past month or so I have yet to try the ASPA routine myself. I've had the AVX out a few times and the goto's seem really good, can't wait to ASPA and take a few photos -Tim

Quote:

Tim,

Thank you very much for clarifying this. It makes sense to me again. Hopefully it will stay that way.

I can also say that I have seen the behavior you describe. The further away I slewed from the synced star used for ASPA, the less accurate it was.




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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795678 - 04/13/13 12:05 AM

Quote:

I am making the assumption that a synced star is one of the two alignment stars. Is that correct or is a sync something different?

What about the calibration stars? Do I need to recalibrate after changing the alignment stars? Do I need to recalibrate after a ASPA?





I find it easier to turn the mount off after ASPA and redo the goto alignment, especially if the polar alignment was way off. You can unsync and replace alignment stars etc, but to me it just seems easier to move the mount to home position, turn it off and on, and start from scratch.

Quote:

Out of 9 frames that were 90 seconds each, 4 had well rounded stars and 5 had slightly oval stars. I did mave the mirror lockup set for the DSLR to prevent vibration from the camera shutter. Not sure if the slightly rounded stars were caused by periodic error or some other cause. It was not windy and the scope was well balanced. Are my results typical for unguided shots?




Regarding your round and oval stars, I believe your results are about average. One of the myths out there is that if you get your polar alignment dead on you will not have tracking issues. The truth is that at short focal lengths and with shorter exposures, moderate polar mis-alignment will only be seen from frame to frame as a gradual movement of the star field across the frame.

If you're seeing star trails and ovals in your subs it's most likely caused by periodic error in the mounts drive gears.

Patrick


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Re: Celestron VX Mount Tracking Test new [Re: Patrick]
      #5795740 - 04/13/13 01:05 AM

Quote:

One of the myths out there is that if you get your polar alignment dead on you will not have tracking issues.




Thanks Patrick. That is what I suspected. I had a similar result with my EQ platform even after a lengthy star drift alignment.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5795812 - 04/13/13 04:00 AM

I didn't mean to cause commotion and have everyone outdoors in an unsyncing party - but it is something simple to try *in case* GoTo is less accurate after ASPA far from the polar alignment star. Syncing shouldn't cause GoTo to be horrible far from the star - but it may make it a little worse.

Patrick's comment above is good because although you don't need to power off after ASPA - some people may prefer to do that because the alignment process steps you through adding calibration stars - and it avoids button presses and menu navigation.

I think the options after ASPA are the following:

1) Do nothing and leave it sync'd

2) Unsync only

3) Unsync and replace the 2 alignment stars (not much menu navigation involved here, so it isn't bad). Although the calibration stars are "gone" - the calibration should still be good after ASPA because only the orientation of the mount changed.

4) If you really want absolute best pointing you can go ahead and do a full realignment with fresh calibration stars - and if you do this then Patrick's approach of powering off may be most efficient because it prompts you through the process.

But in all this stuff - you may not need to do anything after ASPA, and what you do depends on how accurate you want the pointing and how much you mind adding stars again. For me, when imaging I do nothing after ASPA because I just need it polar aligned and then I need to find the target and start imaging - and improved accuracy isn't needed. Sometimes I sync on the imaging target itself in case I need to go away and come back to it, to focus for example.

Frank


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Re: Celestron VX Mount Tracking Test new [Re: freestar8n]
      #5795922 - 04/13/13 05:22 AM

I don't think this debate will get much further without some data in the form of measurements of pointing errors for a variety of sequences of aligning, ASPA and sync.

It's quite easy to measure alignment errors - do a slew to a bright star, centre it and use the identify function on the HC. The selected star should be the first object and you get it's distance from where the mount thinks it should be.

I did some tests like this when I was checking out the mount and found that after a 2+3 alignment the average pointing error was less than 2 arc minutes, I saw values between zero and 4.5 arc minutes, mostly zero and 1.

The polar align error was just over 1 deg in azimuth and 5' in alt.

I didn't do an ASPA and check this again but it would be easy for someone who has a clear sky to try this. Also check the effect of sync.

Chris.


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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5796472 - 04/13/13 11:41 AM

Quote:

The polar align error was just over 1 deg in azimuth and 5' in alt.




Thanks Chris. I am now interested in the polar alignment accuracy itself. How did you determine that? I was planning on following up an ASPA with a CCD/DSLR star drift alignment test.


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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5796637 - 04/13/13 01:29 PM

The HC shows the polar align error.

I think an ASPA should give a good place to do a drift alignment if you feel that one is required. You will have to redo the alignment afterwards because the mount will not be aware of the drift alignment corrections.

Chris


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Re: Celestron VX Mount Tracking Test new [Re: cn register 5]
      #5796676 - 04/13/13 01:55 PM

Ok you were checking the correction that was made during ASPA as reported by the hand controller. I was interested in comparing the resulting ASPA to a star drift. Yes I see the need to realign after making adjustments during a star drift. However based on the results of my test shots so far I can say that the ASPA is very close.

This has been a very helpful thread to me. I want to thank everyone for their advice.


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bilgebayModerator
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5796703 - 04/13/13 02:22 PM

Quote:

However based on the results of my test shots so far I can say that the ASPA is very close.




This is very good to know indeed. Thanks.


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FTLAUDSKY
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Re: Celestron VX Mount Tracking Test new [Re: bilgebay]
      #5797539 - 04/13/13 09:50 PM

OK...I am newbie and have the VX mount now for about 2 months. Keep in mind this is my first mount and it took me about 2 hours to figure out how to get it working. From then on I always would do a 2+4 and by the 3rd or 4th star they would be right in the middle or off by just a little bit. I never ever did a ASPA until recently. I am fortunate and can see Polaris from my backyard clearly. I have align Polaris in the middle of my non reticle EP. This was wrong obviously. After reading about the ASPA I have now incorporated that after my 2+4. Took me a few times to get it right and turn the reticle EP so the star would drift and move along the lines. Afterwards I turn off the mount and do another 2+4. My unguided pictures would start to show star trails after about 60 seconds. With guiding I can do 2-3 minutes. Unfortunately for me after around 3-4 minutes my picture turn white and are oversaturated even with the IDAS V4. Sucks being in the city. I am also by the beach and wind is a constant problem. I am happy so far with the VX just wish it could handle more weight. I am about at the 1/2 load with my scope and gear.


PS - I am now learning how to properly configure the brain settings in PHD and watching the graph after each adjustment to see if it get better or worse. I can tell you I have both RA and DEC moving up and down not far from the middle line. The movements though seem choppy so need to work on the aggressiveness.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: FTLAUDSKY]
      #5798100 - 04/14/13 11:06 AM

Quote:

My unguided pictures would start to show star trails after about 60 seconds. With guiding I can do 2-3 minutes. Unfortunately for me after around 3-4 minutes my picture turn white and are oversaturated even with the IDAS V4.




I have been able to get 2 minute shots unguided with round stars at 430mm focal length. When you use your reticle ep to align, do you Barlow it? Using a Barlow should help with the accuracy.

I have the same problem with light pollution. I have a 2" baader sky glow filter which helps, but I am probably going to be limited to 5 min subs once I start autoguiding.


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5816294 - 04/22/13 08:29 PM Attachment (10 downloads)

The clouds finally cleared and I was able to run the test I have dying to do. I wanted to do a star drift to double check the ASPA. I did the following procedure:
1. Rough aligment on Polaris
2. 2 star alignment
3. 4 calibration stars
4. Polar align mount (ASPA) on a star close to where the meridan crosses the celestial equator
5. Unsync
6. Realign the two alignment stars
7. Perform a DSLR star drift aligment as per http://www.cloudynights.com/item.php?item_id=2838

Here are the results. After the ASPA, the star drift showed that the polar alignment was off in Azimuth but not in Altitude. After correcting for Azimuth, I took some test shots. Star trailing was evident after 3 minutes. This was no different than when I took test shots after just doing the ASPA. For unguided 2 minute shots, ASPA seems to be good enough at 430mm focal length.


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orion69
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Re: Celestron VX Mount Tracking Test new [Re: Jeff2011]
      #5816329 - 04/22/13 08:44 PM

Why are people so obsessed with unguided imaging with low end mounts? I does not make sense, you just don't do that. As for 2 min of unguided imaging, sometimes it will be ok, sometimes not. It's not repeatable (because it's a low end mount) and that is why it is not relevant.

As for ASPA, it's very usable for AP, nearly all my images were shot after ASPA.

Edited by orion69 (04/22/13 08:46 PM)


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Jeff2011
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Re: Celestron VX Mount Tracking Test new [Re: orion69]
      #5816392 - 04/22/13 09:19 PM

Quote:

Why are people so obsessed with unguided imaging with low end mounts?




Because us low enders are facinated by our equipment and want to see what we can get out of it after paying a pittance for it.

In all seriousness, that is good advice Knez. To a seasoned astrophotographer as yourself, I can see how my topic may be irrelevent. This is all still rather new to me, so I like to find out what the equipment is capable of. And yes, I have been finding out that unguided imaging is unrepeatable. Some of us just have to learn the hard way.


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