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Hughsie

Is the initial star alignment necessary if you plate solve?

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I use the Celestron AVX mount and I also use Astrophotography Tool when imaging.

When I start my imaging session I will undertake a two star alignment then move to my target and THEN platesolve to ensure I have the object centred.

My question is do I need to bother with two star alignment (or any other Celestron alignment for that matter)? 

My thought would be to Polar align then take a shot of Polaris and plate solve this, sync the result to the mount then “Goto” from there. The only issue I have is when you switch the mount on and enter time/date etc it asks you to do a star alignment so how do I ignore this or do I do just that, ignore it!

Sorry for the rambling question.

john

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I'd say no, as my mount is fixed, I just need to check Polar alignment every few months, but after that I just instruct SGPro\APT to slew & then plate solve...

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I'm pretty sure you can just ignore it ... sorry, the little devil on my shoulder is begging to ask Dr JuJu how he's getting on with the ASI - 16000mm 🙂

 

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I agree with the others on here. I don't have a fixed setup and all I do is polar align (using Sharpcap) then plate solve and slew to my target using APT GoTo++ .  It works great. Don't have to do any other type of alignment and it saves a lot of time.

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I have never Star Aligned at all. Always use APT and just Plate Solve after PA.  Not sure about what to do on the Star Alignment option as use EQMod but would have thought to just ignore it.

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Posted (edited)

Effectively, in APT after the platesolve where you press 'sync' you are actually doing a very accurate one-star alignment*. If you move to a different area of the sky and do a second platesolve and sync you have done a very accurate two-star alignment. 

Ady

 

* I'm just remembering the days when I did manual star alignments without an eyepiece with the illuminated cross-hairs. That was really, really inaccurate :lol:

Edited by adyj1
clarification

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Nope I never do intial star alignment , just set scope in home position , slew to what I need to image and then platesolve using APT , then use the GOTO ++ to centre the image.

 

 

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Ady is correct. All those folks who platesolve and say they don't align are only half right. Plate solving itself doesn't cange anything, but the act of synching, which is usually an integral part of the plate solve goto sequence, is what performs the alignment and is what allows the mount/driver to provide position correction. This is exactly the same as one star alignment except you can align closer to target and without being centred on a star. I guess the ease and convenience of the plate solve / goto process means many folks don't have to consider exactly what is happening behind the scenes, but if you platesolve and sync you are performing alignment.

Chris

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20 minutes ago, chrisshillito said:

Ady is correct. All those folks who platesolve and say they don't align are only half right. Plate solving itself doesn't cange anything, but the act of synching, which is usually an integral part of the plate solve goto sequence, is what performs the alignment and is what allows the mount/driver to provide position correction. This is exactly the same as one star alignment except you can align closer to target and without being centred on a star. I guess the ease and convenience of the plate solve / goto process means many folks don't have to consider exactly what is happening behind the scenes, but if you platesolve and sync you are performing alignment.

Chris

/Pendant

As the rest of the posters have indicated you don’t need to waste time aligning on a random bright star when you can align on your target directly ie platesolve. I dont do an initial star alignment either and have no issues  

 

 

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Thank you everyone for your replies. That’s cleared it up in my own mind and will save a lot of kneeling down looking through a red dot finder 👍🏻

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22 hours ago, Hughsie said:

I use the Celestron AVX mount and I also use Astrophotography Tool when imaging.

When I start my imaging session I will undertake a two star alignment then move to my target and THEN platesolve to ensure I have the object centred.

My question is do I need to bother with two star alignment (or any other Celestron alignment for that matter)? 

My thought would be to Polar align then take a shot of Polaris and plate solve this, sync the result to the mount then “Goto” from there. The only issue I have is when you switch the mount on and enter time/date etc it asks you to do a star alignment so how do I ignore this or do I do just that, ignore it!

Sorry for the rambling question.

john

If your plate solving then I think a 1 star alignment is fine..I've heard of some thst plate solve on Polaris but.. why not return to home position on your AVX, goto the utilities tab in the menu , scroll down and find hibernate, do what it says on the handset and switch off.. next time you setup it will say wake up on the handset and all the star alignment is saved..I go for months without star aligning now

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In common with everyone else who has replied to this, I just do a solve and sync in lieu of star alignment after polar aligning, but I don't think anyone has mentioned that it's definitely a good idea to do this well away from the celestial pole.  Plate solving near the pole is likely to give rise to some significant alignment errors, so I generally try to get somewhere with Dec < ~50° for my first solve/sync.

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Posted (edited)
On 23/05/2019 at 13:52, GraemeH said:

In common with everyone else who has replied to this, I just do a solve and sync in lieu of star alignment after polar aligning, but I don't think anyone has mentioned that it's definitely a good idea to do this well away from the celestial pole.  Plate solving near the pole is likely to give rise to some significant alignment errors, so I generally try to get somewhere with Dec < ~50° for my first solve/sync.

I am confused by what you said. I do plate solving to reach and center my target (it replaces the GOTO fonction and 3 stars alignment) once the scope is on target and I need to go to another target I just plate solve again.

What I do not understand is why are you talking about significant alignment error ? Are you refering to polar alignement ? Once you are polar aligned, you stay plolar aligned no matter where you plate solve, at the pole or anywhere else. Could you clarify as I may have misunderstood something and getting it wrong.

Thanks!

Edited by Vox45

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On ‎24‎/‎05‎/‎2019 at 16:55, Vox45 said:

I am confused by what you said. I do plate solving to reach and center my target (it replaces the GOTO fonction and 3 stars alignment) once the scope is on target and I need to go to another target I just plate solve again.

What I do not understand is why are you talking about significant alignment error ? Are you refering to polar alignement ? Once you are polar aligned, you stay plolar aligned no matter where you plate solve, at the pole or anywhere else. Could you clarify as I may have misunderstood something and getting it wrong.

Thanks!

Sorry for not being clear - I meant error in star alignment arising from platesolving close to the pole, and nothing to do with polar alignment.  If you solve/sync close to the pole, your next Goto could be quite far off.

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On 27/05/2019 at 11:42, GraemeH said:

Sorry for not being clear - I meant error in star alignment arising from platesolving close to the pole, and nothing to do with polar alignment.  If you solve/sync close to the pole, your next Goto could be quite far off.

Thank you for clarifying. I understand what you mean.

What I like about plate solving and why I stopped doing 3 stars alignement is that I can now move from target to target using solve (and sync) and after a couple of targets the model is as good as doing a 3 stars alignment and with each targtet the model gets refined to 4, 5, 6 stars and on and on ;) 

I had issues at first with the solving not completing or taking a long time. With the proper settings: making sure I entered the correct FOV, only using the index file I need (too many uneeded index files slow down the process) I always solve under 10 sec.

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