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Synscan 1/2/3 star alignment - just for Go To?

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#1 CapPic

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Posted 09 October 2012 - 01:55 AM

I have a dumb question about my Atlas mount. Is the alignment solely for synching the Go To function or does it do something to compensate for error in polar alignment?

#2 Tapio

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Posted 09 October 2012 - 02:36 AM

Alignment doesn't compensate for polar alignment.
So you should do it first before alignment.
Rough polar alignment is enough if you do just visual gazing but you should do better PA for imagining purpose.

#3 rmollise

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Posted 09 October 2012 - 06:48 AM

It is for go-to alignment. BUT...the results of the alignment ARE used for calculating polar alignment errors when you do the HC's (in the beta release of the new software) polar alignment procedure.

#4 CapPic

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Posted 09 October 2012 - 12:43 PM

Thanks for the responses.

Last night I did my first proper polar alignment (that was great for visual - Jupiter at 180x stayed centered for a good length of time). I'm now looking at the next step of correction so that I can do long exposures for AP.

I have a serial-to-USB cable coming this week so that I can update the firmware and try that new polar re-alignment feature. Any idea how well that feature compares to something like drift alignment?

#5 Steve Drapak

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Posted 16 October 2012 - 01:46 PM

You can try the CCD Drift Alignment method as well. It's a little less tedious as you don't have to sit and watch it quite as much. You should be able to use to get to an accuracy where stars don't move a pixel for a number of minutes.

#6 jrbarnett

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Posted 16 October 2012 - 03:17 PM

I experienced something curious last Saturday. I started out the session with an Astrotelescopes 152mm f/5.9 achromat on the Atlas. The OTA is on the long and weight side; about 3-feet long and ~25# all dressed up. I used a three star alignment routine (Arcturus, Vega and Caph, if I recall), and rough centering of alignment stars in a low power eyepiece (27mm Panoptic). GOTOs were good but not perfect, with targets appearing in the FOV of a medium power (14mm S4K UWA) but not near center for the entirety of the session with that scope.

Round about eleven, the big achro dewed up, so I pulled it, put it in the car, replaced it in the saddle with the smaller, lighter AT111EDT, started up the Atlas and re-aligned, this time using a 2-star alignment routine, the same low power eyepiece and same rough centering.

The GOTOs were perfect with the object nearly dead-center for the rest of the night until dew claimed the second OTA after midnight.

I'm not sure what to make of the difference in accuracy between the two alignment routines. My hunch is that I either did a better job centering the alignment stars the second time around (not consciously but by luck) or the smaller, lighter OTA helped the mount's accuracy. :thinking:

- Jim

#7 rmollise

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Posted 16 October 2012 - 05:25 PM

Hard to say, but my guess would be Vega was the culprit. My experience has been "don't use stars too close to the "Local Meridian."

#8 jrbarnett

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Posted 17 October 2012 - 11:49 AM

Thanks Rod.

I'll play with it this weekend and try a variety of different alignment stars and an illuminated reticle eyepiece for centering.

- Jim

#9 rmollise

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Posted 17 October 2012 - 11:55 AM

The last time I used Vega, during last month's dark run, my go-tos were not as good as they normally are with the Synscan.

#10 jean-pierre

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Posted 20 November 2012 - 04:18 PM

I have a Synscan with an equatorial mount (HEQ5).
I thought possible to make a 3 Stars alignment without previous polar alignment.
It seems that it is not possible: the sky mapping is not correct at all. The Goto does not “go to” the location I want.
I’m surprised as geometrically, it should work:
- Given the stars A and B, the angle APB being constant and known in the Synscan database, the loci of points P (where Polaris is) is a circular arc.
- Given the stars A and C, the loci of points P is a second circular arc.
- So Polaris is at the intersection of those two arcs.
Can you tell me why it does not work?
Thank you.
Jean-Pierre

#11 neptun2

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Posted 22 November 2012 - 09:45 AM

I usually use 3-star alignment and select the stars that synscan suggests. First star is usually several degrees off (even out of the field of view of finderscope). I center the stars using my DSLR live view and a grid which makes the process very accurate. After centering the first star the second is in the field of view of the finderscope and the third is usually in the field of view of the DSLR. After completing the 3-star align i make the new polar align routine and both the goto accuracy and the polar alignment are very good at the end.

#12 groz

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Posted 01 December 2012 - 12:11 PM

The problem with using the default choices of the synscan, it'll prompt you for the brightest, ie easiest to find stars, which dont always give best alignment. Always avoid stars high near zenith, particularily for the first star.

We rarely take the first choice, but scroll down the offered list. First star on the west side (because we have a better view to the west), then second star also on west side, well displaced from the first. Third star on the east side of meridian. Avoid anything up near zenith.

Once we had this sorted out in our minds, alignments have never been a problem for us. We have been using a eq6-pro (his) and an heq5-pro (hers) this way for years.

#13 rmollise

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Posted 01 December 2012 - 02:53 PM

The problem with using the default choices of the synscan, it'll prompt you for the brightest, ie easiest to find stars, which dont always give best alignment. Always avoid stars high near zenith, particularily for the first star.

We rarely take the first choice, but scroll down the offered list. First star on the west side (because we have a better view to the west), then second star also on west side, well displaced from the first. Third star on the east side of meridian. Avoid anything up near zenith.

Once we had this sorted out in our minds, alignments have never been a problem for us. We have been using a eq6-pro (his) and an heq5-pro (hers) this way for years.


Amen to all that. I will say, however, that based on my testing of the new Synscan firmware down in Chiefland a couple of months back, the choices offered by the HC are _usually/sometimes_ better:

http://uncle-rods.bl...-ii-nights-1...

#14 RandallK

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Posted 01 December 2012 - 06:49 PM

Yep...I think Vega should be taken out of the sky. Gives me trouble everytime I choose it in a 3 star alignment process.

#15 neptun2

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Posted 02 December 2012 - 11:16 AM

Well this is interesting. I always use the stars suggested by the hand controller and never had problems even when Vega is used as first star. I always use the live view of my dslr which have grid to center the stars which makes the centering pretty accurate. I also always use 3-star alignment. Maybe thee was problems with the old firmwares but the new ones seem to work well at least for me with my HEQ-5 Pro (sirius) mount.

#16 groz

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Posted 02 December 2012 - 01:01 PM

It's not really that vega is the problem, its choosing a star near zenith. In our part of the world, vega is often very close to zenith in the early evening when we are in the 'good astronomy weather' part of the year, which makes it problematic in the alignment math.






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