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Equipment Discussions >> Mounts

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Jeff2011
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Reged: 01/01/13

Loc: Sugar Land, TX
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
scholastic sledgehammer


Reged: 12/26/12

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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Loc: Sugar Land, TX
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
scholastic sledgehammer


Reged: 12/26/12

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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Reged: 01/01/13

Loc: Sugar Land, TX
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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cn register 5
scholastic sledgehammer


Reged: 12/26/12

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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Reged: 01/07/05

Loc: NE Ohio
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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Raginar
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Reged: 10/19/10

Loc: Rapid CIty, SD
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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cn register 5
scholastic sledgehammer


Reged: 12/26/12

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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Reged: 10/19/10

Loc: Rapid CIty, SD
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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cn register 5
scholastic sledgehammer


Reged: 12/26/12

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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Reged: 10/12/07

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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Reged: 01/07/05

Loc: NE Ohio
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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Stew57
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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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Reged: 01/07/05

Loc: NE Ohio
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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Reged: 01/01/13

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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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Stew57
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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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DaveJ
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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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jrcrillyAdministrator
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Loc: NE Ohio
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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