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Synscan V3.35 Polar alignment Option...can't be this easy...can it?

Purplehayze104

By Purplehayze104
in Discussions - Software

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Purplehayze104

Purplehayze104

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Hi All

Thought I would give the polar align option on my Synscan a go after upgrading the firmware on the handset, was a little dubious about it as never really tried accurate polar alignment before as don't have polar scope & I've been roughly aligning with Polaris by taking the caps off the hole through the mount and centralising the star in middle of the opening. well I did a 3 star alignment & looked at the polar alignment error. (1deg 28mins 25sec out in alt & 5mins 34secs out in azimuth) I followed the instructions on the handset chose a star (vega) & went through the processes to eliminate as much of the error as I could using the alt bolts & az knobs. Surprisingly to me only took around 5mins or so to do & low an behold it came back with (0deg 0mins 0secs in alt & only 3secs in az) if this is correct then i'm assuming that it was almost spot on polar alignment, only thing for me is it seemed to easy to do, from posts etc I've read on this site it can take a while to do & get right.

does anyone else use the handset/polar align option as I would like to find out if this is correct & if its really that easy ? I used a 12.5mm SW illuminated reticle eyepiece for this also, for a bit more accuracy.

comments much appreciated

thanks

John

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Stephen

Stephen

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Well yes, I use it and find it that easy however as with anything there are some caveats ...

Firstly ignore the numbers post correction : the handset has no knowledge of how much you have moved the mount in Alt/Az hence it's assuming you did the job correctly :) (you also need to redo three star after adjusting the PA which will give you a different error.)

Secondly, this is an itterative process. I can normally hit 5 minute subs without issue on one itteration ... but there is still error there. Further itterations of the three star/PA routine are recommended (and documented) to increase the accuracy of your PA

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Purplehayze104

Purplehayze104

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thanks for the reply,

arh... just re-read the manual, don't think I read it properly or id forgot the rest which I more likely wot happened, as you've said have to do it a number of times for more accuracy, doing it once isn't really gunna do it :D I really need to learn more patience lol will give it another try if we get a decent sky again hopefully be soon but it does seem a easy enuff process to do.

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knobby

knobby

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thanks for the reply,

arh... just re-read the manual, don't think I read it properly or id forgot the rest which I more likely wot happened, as you've said have to do it a number of times for more accuracy, doing it once isn't really gunna do it :D I really need to learn more patience lol will give it another try if we get a decent sky again hopefully be soon but it does seem a easy enuff process to do.

At least you actually read the manual :-)

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PhotoGav

PhotoGav

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Hi folks,

I've been trying to suss out this Polar Align function and have been struggling a bit. I have been setting up with as good a polar alignment as I can manage, doing a 3-star alignment and then doing the polar align. It's told me that it's a few minutes out on both Alt & Az and is generally worse after the first go and a subsequent 3-star align. So I do another polar align and I'm still a few minutes out... On it goes.

So, where am I going wrong??! Probably a tricky question to answer, but any advice on how to do this polar align properly would be greatly appreciated.

Cheers,

Gav.

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OzDave

OzDave

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There are a lot of factors at play here. Firstly, if your mount is not completely level, when you make an AZ adjustment you are also making a simultaneous ALT mis-correction because the axes are not aligned to the horizon properly due to not being level. So when you correct as it suggests, you're sort of just changing the error from axis to axis on each iteration through the procedure.

The second thing is the the way the synscan models the PA errors is from the 3-star alignment errors that you had to correct. But it is not only PA errors that cause those errors. Could be cone error, ra or dec axes not properly zeroed in the home position, slightly incorrect time of day or GPS position, or manufacturing defects in the mount causing small positioning errors.

Since there are only 3 stars to provide data for the error modelling, it is impossible to take them into account and so the synscan has to assume everything else is perfect except PA error and maybe it can account for cone error too. So the upshot is, if you have significant errors in other aspects of your setup that synscan is assuming to be perfect, then you will likely find that you cannot get accurate PA with this system even if it says you have.

What you may succeed in doing is getting it to tell you the alignment is very close, but in fact it will still be off due to all the other errors in the setup that are assumed perfect. I suspect that you'd get close enough though for most observing purposes though. For astrophtography you'd still want to drift align.

Hope this helps.

David

Sent from my iPhone using Tapatalk - now Free

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PhotoGav

PhotoGav

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Thank you David for your detailed response.

Yes, many factors at play indeed. I will pay closer attention to the tripod leveling next time, though I am pretty accurate with that already. Perhaps I am just expecting too much from this function? As you say, drift alignment could be the best solution.

Maybe I just need to bite the bullet and expand my gear to include a guiding set up. I have embarked on the astrophotography journey, so the more accuracy the better.

Cheers,

Gav.

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OzDave

OzDave

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One thing you could do is get it aligned till the synscan says you're pretty close, then do a drift align to see if it is really lying to you. I suspect you'll find that a drift align will reveal you are still off if you still have errors elsewhere.

That would be an interesting bit of research to post here.

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OzDave

OzDave

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Google is your friend. Some tutorials are better than others. Find several, pick one that makes the most sense to you. Some of them even explain the theory in simple terms for why drift alignment works the way it does.

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PhotoGav

PhotoGav

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Cheers Steve, that looks well worth a try. One question though - it says to 'Set your telescope to point due south at 0 degrees Dec' should this be done by slewing the scope from home position with the keypad or should I unlock the axis and move it there manually?

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OzDave

OzDave

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Cheers Steve, that looks well worth a try. One question though - it says to 'Set your telescope to point due south at 0 degrees Dec' should this be done by slewing the scope from home position with the keypad or should I unlock the axis and move it there manually?

Personally I'd slew with the keypad otherwise you'll have to reset the home position and restart synscan so it knows you are synced at home. If that isn't a big deal, just declutch and move.

Sent from my iPhone using Tapatalk - now Free

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Stephen

Stephen

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Personally I'd slew with the keypad otherwise you'll have to reset the home position and restart synscan so it knows you are synced at home. If that isn't a big deal, just declutch and move.

Sent from my iPhone using Tapatalk - now Free

Though to be fair if you're drift aligning you're going to invalidate the handset anyways as soon as you start adjusting the Alt/Az so I guess it doesn't really make a difference?

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ajohnson

ajohnson

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I've tried this option a few times and given up in frustration, as has been mentioned the software assumes a lot about the accuracy of your levelling etc. Even once I worked out I had some cone error and corrected it I found this utility was only useful in frustrating me. You can get a zero error on you handset by starting the process and just hitting enter a few times so even after making your adjustments you have to do another 3 star align, annoyingly after doing all of this you may or may not get a reduced error.

I found the best way was to use the polar scope and Polar finder to get alignment as close as possible with the polar scope and run the 3 star alignment process. I usually get errors in minutes as a start point, I have then found that drift aligning is actually quicker / less frustrating using the following methods http://www.astrotarp.com/tutorials.html. This pushes the mount's view of the sky off a bit but you can correct this using PAE adjustment.

Finally as I have been bitten by the AP bug I found that even with crackerjack polar alignment my 12" Newt never did much better than 2 minute photos without trailing so I invested in a guider which to a greater extent has made life easier. Even with the guider good polar alignment is essential as this cut's down the corrections the guider needs to make to stay on track

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lensman57

lensman57

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Cheers Steve, that looks well worth a try. One question though - it says to 'Set your telescope to point due south at 0 degrees Dec' should this be done by slewing the scope from home position with the keypad or should I unlock the axis and move it there manually?

Hi Gav,

I have been using the Polar Align routine since the new firmware appeared a while back. I could do 20 minutes subs on my EQ5 PRO ( now sold ) and I have done 20 minute subs on my new HEQ5 PRO. Polar Align will get you close enough that you can do the longer subs provided that your set up is perfectly balanced and the mount level, it will never be perfect and I don't think it was ever designed to to be so. The problem with all the other methodes of polar aligning are:

1 They all assume that you have unrestricted horizon around you.

2  that your scope is permanently parked in an obsy.

Mine has to be carried into my back garden, set up levelled and then aligned, I usually do 3 cycles in about 10 minutes, if I am not over tired from my regular work, and so far the results have been OK for me.

A.G

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lensman57

lensman57

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A.G. That's pretty impressive. You have obviously mastered the dark art of Polar Align! What kind of values do you get for the Polar Alignment Error after the three cycles? Are the 20 min subs unguided?!

Hi Gav,

With regret I wish my subs were unguided, for that I think I would need a 10 Micron GM1000 mount which would leave me little change out of £7000.00. I don't particularly give not much time to the figures given by the hand set but I know that when I close enough the mount would only move the star just a little bit out of the centre of the eyepiece, while I am way off sometimes the star gets out of the FOV of my 50 mm finder on the first cycle. With HEQ5 and a good polar alignment unguided subs of 120s are possible with a short fast refractor scope, the longer the focal length the more accuracy is required.

Regards,

A.G

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