Any Fine-tuning tips for SkyWatcher SynScan Alignment?

[JonCarleton]

I know I am getting picky, and have really had pretty good luck with my scope for the little time I have had with clear skies since I got it.  But, my alignments aren't as rock-solid as I'd like them to be.  For example, on a bright night (moon), I can do my typical align and then look for a deep sky object..some galaxy or nebula...and it -nearly- gets it right.  On a dark night, I can fiddle around and find the objective, but when it is bright, if it doesn't land "slap on it," I'm in trouble.  And, it doesn't.  Most of the time it is fairly close, but never the bullseye.

The routine I use, as carefully as I can is:

1. Level the base of the Dobsonian mount with shims.

2 . Point the scope True North (not magnetic) and level the tube (bubble-level).

3. Turn on the Synscan unit and enter exact data for time, date, Lat/Lons and etc.  I am a pilot and am used to being careful about these data.

4. Perform a 2 star alignment with the hand unit (sometime I use the 3 star with the Android App, but it doesn't seem to matter), being careful to select stars at least 90 degrees away from each other in the sky.

5. On "Alignment Successful," I proceed with selecting a target for it to find.

I am careful to center the object in the eyepiece at each stage, using the remote controls of either the hand unit or the App.  I try not to touch the scope at all once I start the alignment process and after it is aligned. As I said, it gets pretty close, but never the bullseye.  I use a 25mm lens for aligning and have tried moving to a 10mm to make sure of centering, though that didn't seem to make any difference.

Any suggestions, tips and tricks would be most welcome.

 

[Tim]

I'm not sure about that particular model, and it has been a while since I've used a Skywatcher alignment routine,  but the way to get pinpoint precision when I had a SW mount was to do a 3 star alignment using a triangle that encompassed the area of sky interest. When you wanted to observe another area of sky, just clear the align and redo another triangle of stars around the target area. Might be worth a shot????

[Star Struck]

You might get better centering during alignment with a dedicated reticule eyepiece.

Trying to center with a 25mm eyepiece may be too inaccurate.

[Aramcheck]

During alignment you could consider using an illuminated reticule eyepiece, but I'm not sure what the limitations are on a GoTo Dob.

Cheers
Ivor

PS:  Sorry  @Star Struck beat me too it.

Edited March 11, 2020 by Aramcheck
Suggestion already posted, whilst typing reply...

[Neil H]

Hi you can also defocus the star so it's easier to get it centred 

Mine is a little off as well so would be nice to find the answer I have only used go-to twice so I have a fair way to go 

Do you have the synscan app gives you all the data you need to put in the handset 

[Owmuchonomy]

Make sure the item (from memory) 'enable auxiliary encoder' is turned OFF when doing your alignment procedure.  You can turn it back on when aligned.  My 12" Synscan Dob used to be very accurate on GoTo but the levelling as you point out has to be spot on.  Good luck.

Edited March 11, 2020 by Owmuchonomy

[Phillips6549]

11 hours ago, Tim said:

but the way to get pinpoint precision when I had a SW mount was to do a 3 star alignment using a triangle that encompassed the area of sky interest.

+1 for this course of action.  Even a 2 star alignment on stars close the the object of interest gives me a huge increase in goto accuracy.

[JOC]

Mine is very sensitive to Eyepiece weight.  If necessary use just the cheap, light plossl EP's that came with the scope.  Even when it's 'driving' to locations I find it's better to drive it with as little weight in the EP holder as possible and then add my EP's when it gets there.

[JonCarleton]

Excellent!  Lots of good stuff as I expected.  Interesting that the consensus seems to be to target a smaller area of the sky.  I have been doing the exact opposite.  I have tried to encapsulate the entire sky with my star choices with the widest possible distance and angular variance. 

I'm going to check that "enable aux encoder" thing as well.  What *IS* an auxiliary encoder and what does it do?

Weight may be an issue.  I'll have to be careful with that.  It certainly doesn't take much to override the motor clutches.

And yes, the reticule eyepiece seems a good idea as well as defocusing the star.  Very clever stuff.  THANKS!

[JOC]

13 hours ago, Tim said:

I'm not sure about that particular model, and it has been a while since I've used a Skywatcher alignment routine,  but the way to get pinpoint precision when I had a SW mount was to do a 3 star alignment using a triangle that encompassed the area of sky interest. When you wanted to observe another area of sky, just clear the align and redo another triangle of stars around the target area. Might be worth a shot????

I must admit I've never tried that - I thought the standing advice with this sort of thing actually was to pick stars that weren't too close together and hence I've also always picked stars a long way from each other.

[Captain Scarlet]

15 minutes ago, JOC said:

... I thought the standing advice with this sort of thing actually was to pick stars that weren't too close together and hence I've also always picked stars a long way from each other.

that's been my understanding too.

If you choose stars that are close together, I think any error in your centering will be greatly amplified the further away you get from your alignment stars.

If I want accurate go-to, I use a reticule eyepiece to get the stars exactly centred; I do my polar alignment with full load; and before starting I delete any user-settings, such as historical PAE adjustments (which, I understand, effectively tell the handset: "THIS is where the target I chose actually is").

[Owmuchonomy]

1 hour ago, JonCarleton said:

Excellent!  Lots of good stuff as I expected.  Interesting that the consensus seems to be to target a smaller area of the sky.  I have been doing the exact opposite.  I have tried to encapsulate the entire sky with my star choices with the widest possible distance and angular variance. 

I'm going to check that "enable aux encoder" thing as well.  What *IS* an auxiliary encoder and what does it do?

Weight may be an issue.  I'll have to be careful with that.  It certainly doesn't take much to override the motor clutches.

And yes, the reticule eyepiece seems a good idea as well as defocusing the star.  Very clever stuff.  THANKS!

The encoders register any untoward movement you may inflict by accident e.g., nudging the scope after alignment and can compensate for it. Best GoTo alignment is achieved with that function OFF.

[Star Struck]

The following came from the Synscan handset manual:

Rules for choosing alignment stars:
• It is recommended that the altitude of the two alignment stars are between 15 and 60
degrees and the deviation in altitude is between 10 and 30 degrees.
• The azimuth deviation of the two alignment stars can be between 45 and 135 degrees, it is best to be close to 90 degrees.

When centering an alignment star in the eyepiece, the operation should always end by using the UP and RIGHT direction keys to move the axes.

[Phillips6549]

58 minutes ago, Captain Magenta said:

If you choose stars that are close together, I think any error in your centering will be greatly amplified the further away you get from your alignment stars.

Yes absolutely.  But if you want to, for example, GoTo an object which is barely visible or invisible in the eyepiece then choosing alignment stars which are close together and close to your target does (in my limited experience) give the best results.    If you then move to another target, you will need to re-align close to that one.

 

3 minutes ago, Star Struck said:

Rules for choosing alignment stars:

The 'rules' are recommendations intended to allow your GoTo system to get you  close to #any# target.  Rules notwithstanding, choosing close stars really helps for one specific target.