Synscan alignment

[chiaroscuro]

More questions about alignment from me!:shrug:

After doing a 2 or 3 star alignment (successful one), the synscan controller gives an alt and azimuth reading. Are those the errors in alt and az that were detected in centring the stars in the eyepiece? Should those angles be used to adjust the mount and realign - I've assumed that would only be necessary for photography tracking where the accuracy is required. Is that correct?

Thanks in advance.

Luke

[Camelopardalis]

If you're using the more recent Synscan versions, it's the error in polar alignment IIRC.

After the 2 or 3 star align, you can go into Align->Polar and it will guide you through steps to make your polar alignment better. So long as your polar alignment isn't too way off already, just the 2 or 3 star alignment should be good enough for visual, but I've been using the polar alignment feature for the last few sessions and it gives spot on gotos all over the sky :) or maybe I got lucky :D

[chiaroscuro]

Thanks Dunk. I'm using version 3.27 (from memory). I've just looked at a youtube clip that says the alignment can be improved by centering another named star (after 2- or 3-star alignment) and pressing the esc key twice (second time for 2 seconds) which then improves tracking accuracy.

BTW, what do you mean by IIRC?

Cheers
Luke

[Camelopardalis]

IIRC = if I remember correctly

3.27 doesn't have the polar correction, but that's an interesting function I'd not heard of :)

[Steffen]

After 2- or 3-star alignment the hand controller will display the polar alignment error it determined. This error has no bearing on the pointing accuracy, but on the ability of the mount to track objects for longer periods of time.

I don't remember 3.27 too well, but in later versions the procedure you describe appears to be PAE (pointing accuracy enhancement). It is only effective in the vicinity of the star used for PAE. The sky is subdivided into 80+ PAE regions IIRC. PAE is helpful for finding faint stuff you may or may not be able to see. At least you'll know it's in the centre of the field that way.

Cheers
Steffen.

[kosh]

Reading the manual for the latest synscan firmware, you use the function under "alignment/polar alignment" after a 2 or 3 star alignment. Ths as you said, gives you an altitude/azimuth error, which in effect tells you how far out from polar alignment you are.

You dont use your controller to make adjustments, only the altitude and azimuth knobs on the mount. You shouldn't be too far away to begin with.

Far as I can tell, PAE is a Different function.

[chiaroscuro]

Hi Kosh,
Thanks for that info. How do you know how much to adjust the alt/az knobs given that the setting circles don't have the precision to do this to that degree of accuracy?

Last weekend I used the esc button to correct centering on a defined object, but it did not seem to make a difference to subsequent accuracy. As Steffen says below, the software isn't able to extrapolate this correction to the whole sky as the Synscan algorithm divides the sky into different regions (I think thats what Steffen means).

I'm curious how this centering correction differs from Polar ALignment Error function too. If anyone can enlighten me, I'd really appreciate it.

Cheers,
Luke

[Larryp]

Hi Luke-if you haven't got an instruction manual, you can go to SkyWatcher's website and download it, as well as later versions of Synscan software.
The instructions explain very well how to improve polar alignment after you do your initial 2 or 3 star alignment:)

[Steffen]

By PAE I meant "pointing accuracy enhancement", it's got nothing to do with polar alignment.

There are two methods for accessing PAE – via the PAE menu under Utility, or by pressing and holding ESC for 2 seconds, like you said. Both should have the same effect. This effect is limited to the zone the object was in, and neighbouring zones. I'm not sure how big those zones are or how they are shaped, the manual doesn't say, but there are 85 of them.

PAE data is kept until explicitly deleted or until another star alignment is performed.

Cheers
Steffen.

[Camelopardalis]

Yeah the assisted polar alignment and PAE functions aren't the same.

With the align->polar function it slews away from a star of your choice and then you adjust the alt and az bolts to centre the star again. You need to re-run the star alignment after this procedure. Using this at the weekend I reduced my azimuth error from 10 degrees to a little more than half in the first iteration. Plenty good enough for visual and the gotos were good all night with my cat, as they should be!

[kosh]

Hi dunk, Im thinking of flashing my synscan from 3.27 to the latest firmware just for this feature. So you think it works well?

[chiaroscuro]

OK, its becoming clearer to me now. Thanks again to you both for your clear explanations.

Hi Larry,

To be honest, I find the explanations in the Synscan manual a little unclear, because they don't really make explicit or clear the differences as Steffen and Dunk outlined. Its always helpful to tap into others experience and wisdom too!

[Camelopardalis]

For visual, so far so good ;) Saturday was my 4th session on 3.35 and it seems to do the job, even when I'd stuck the tripod down barely in the general direction of the celestial pole (by 10 degrees!) it managed to guide me through it. So using myself as the example, it seems fairly idiot proof :D I'm from up north so used to having a mag 2 star in the polar scope :lol:

[kosh]

Im going to definitely give it a go. Im using the scope for AP so any significant increase in tracking time should help while I save them pennies for an autoguider solution.
Cheers.

[chiaroscuro]

Actually, I checked last weekend, and I'm on 3.35 too, and haven't had any major problems. I spend quite a bit of time trying to point at the SCP first (got within 1 degree in both alt and az just with visual alignment through the finder scope), and then do a 2 -star alignment and then PAE.

One of the reasons I'm becoming a bit obsessed with this is that I've been trying to see Neptune and Uranus, but when the scope tracks to that part of the sky, I'm not sure which of the bright dots in the FOV is the planet I'm after! I can convince myself that any number have a blue or green tinge.

[Camelopardalis]

Ah I see, well it works great without even using the polar scope... it's even called that in the manual :D :D (section 11.3)

If you're polar aligning with the polar scope to within 1 degree, you may not gain all that much, but every little helps... when you're doing your 2-star alignment, it's important to accurately centre the alignment stars in the FOV, so use a high magnification and narrow FOV eyepiece, or ideally a reticle eyepiece (has the crosshairs in the centre).
Polar aligning more accurately is important for long exposure AP, but for visual you should be able to get by with a good 2-star alignment. So far I've not used PAE but somehow the polar alignment function works reasonably well for me even with my scope FL=2800mm. Maybe it's just luck, but reproducible so far.

Neptune and Uranus are quite distinctly coloured, and Uranus quite bright (about magnitude 6 at the moment). One trick with them if you're not sure is to increase the magnification... what will happen is the planets become fuzzy disks, whereas stars will remain small points.

[Astro_Bot]

The polar scope can produce better results than that. When I used v3.35, my Mel and Maz were typically less than 10 arcminutes when using the polar scope, which is indeed quite good enough for visual or even short-exposure AP. But, true to say, for visual, you don't need to polar align.

I found (but have done no specific experiments, so may change my mind with better data) that GoTo accuracy was a tad better if I'd polar aligned first (though that was using v3.27).

For imaging, when using EQMOD, I've heard that programs like Alignmaster can routinely achieve about 1 arcminute polar alignment accuracy, while other programs can do even better (Edit: though I figure that'd be with a better mount than an NEQ6, given how fiddly the adjustment bolts can be) ... but I'm still an L-plater when it comes to that stuff.

[chiaroscuro]

I find it very difficult to see octans through the polar scope. I could blame it on its aperture, but I think its just me, although I can barely see anything through the polar scope.
I know its not really necessary to be so accurate for visual, but it seems like a fundamental skill for astronomy and for a smooth transition into astrophotography, if I ever take that daunting step. My next step is to learn how to drift align, now that I've got a reticle eyepiece.

[Astro_Bot]

Yes, it's hard, especially from the suburbs. However ...

Finding Octans is made easier if you follow this procedure for SynScan mounts first (in fact, maybe I'll write this up for an arcticle, if other people find it useful):

Note: You only need to carry out this procedure once!

1. Roughly align and level your mount by whatever means you have available, e.g. compass and bubble level - a level tripod is helpful later so try and get it as level as you can
2. Power on your mount (which is necessary to illuminate the polar scope reticle anyway) and enter date, time, timezone and coordinates as per usual
3. Use a star chart, or planetarium program, to get the approximate orientation of the Sigma Octans asterism at your present time and location (remember that the polar scope inverts the image)
4. Rotate your mount in the RA axis so that the reticle orientation matches the Sigma Octans asterism at Step 3
5. Observe through the polar scope and adjust Azimuth and Elevation bolts to bring the Sigma Octans asterism close to the reticle - this may take some time depending on how accurate your rough alignment was at Step 1
6. Iteratively adjust the RA axis rotation and Azimuth and Elevation bolts to align the Sigma Octans asterism with the reticle - this may take some time and you will have to keep rotating the RA axis clockwise as time progresses - take your time and get it spot on
7. As soon as you have achieved as good a polar alignment as you can, lock the RA axis then read the Polaris Hour Angle from the SynScan handset - you may want to have that screen displayed ready
8. Note down the Polaris Hour Angle and, without moving the RA axis, loosen the RA setting circle thumbscrews
9. Rotate the setting circle so that the index mark (pointer) points to the Polaris Hour Angle noted at Step 8 using the Southern Hemisphere (lower) numbers
10. Tighten the RA setting circle thumbscrews being careful not to move the setting circle - you can use pliers for the final tightening twist if you find your fingers slip but there's no need to overtighten

Now, whenever you want to orient the polar scope reticle to the correct orientation of Sigma Octans, simply read off the SynScan-generated Polaris Hour Angle and rotate the RA axis until the index mark (pointer) points to the same time. Knowing the correct orientation makes recognising the Sigma Octans asterism much easier and quicker.

The SynScan-generated Polaris Hour Angle is corrected for location, date, time and timezone, so should work anywhere in the Southern Hemisphere without having to re-adjust the RA setting circle.

You can substitute another Polaris Hour Angle or Sigma Octans Hour Angle calculator in place of SynScan as long as you use the same one each time.

If your rough mount alignment at the start of your session is within about 3 degrees azimuth (quite achievable when using a compass) and you have left elevation set from your first polar alignment (on a level tripod), or pre-set it with a protractor or inclinometer (rather than the notoriously inaccurate elevation scale), then you should see the Sigma Octans asterism in the polar scope every time (light pollution permitting). This permits polar alignment in around 5 minutes.

[Steffen]

Luke, forget about drift aligning a SynScan EQ mount, it's a waste of time (except of course for the CCD based variant, which is fast and accurate).

I get sub-arcminute polar alignment with little effort and the help of SynScan v3.35. With some input from forum mates (esp Wavy) and recent practice I think I have it down pat now. Here's what I do:

The altitude adjustment is straightforward, the elevation scale on the mount and/or a clinometer on the counterweight shaft gets you close enough for the software to finish it off. For azimuth, the trick is to find south, of course. With cars, mounts, steel tripods etc around magnetic compasses have a hard time making up their mind.

Starting with the mount in "home position" (counterweight shaft at its lowest position, OTA parallel to RA axis) I simply guess the south direction and start a 1-star alignment. The RDF or finder scope will miss the alignment star by some amount, depending on how well I guessed south. I then yank the tripod around to get the scope pointing as close to the alignment star as I can. This will reduce the gross azimuth alignment error.

Next, I run a 2-star alignment to its completion, after which the hand controller will display the alt and az alignment errors. If the az error is less than a degree I move on to the SynScan polar alignment routine. Otherwise I yank the tripod some more and run another 2-star alignment.

From this it takes me two or three runs of the polar alignment routine, followed by a 2-star alignment each time, to get the polar alignment error to under 1 arc minute in both directions. This is much better than I need for visual, but I do it anyway because it's fast and easy to do (provided I can see alignment stars).

For AP you may want to follow up with CCD drift alignment, depending on your planned exposure times.

Drift aligning by looking through a reticle eyepiece takes forever in comparison, is a waiting game and can be a bit of a mind twister.

That said, you will definitely need to use that reticle eyepiece for star and polar alignment. Guessing will only cause frustration.

Cheers
Steffen.

[Astro_Bot]

I agree drift alignment through an eyepiece is frustratingly slow. Fuhgeddaboudit!

[chiaroscuro]

Nice to get some perspective about all this. When I first looked into a GEM, I thought is was essential to have an accurate polar alignment but its become clear that its not so critical for adequate visual tracking.
Anyway, I'll be referring to your posts, Steffen and Astro-bot, next time the scope comes out. You do a much better job of explaining it than the manual.

[Camelopardalis]

Agreed, very good posts :)

Once you've gone through the motions a few times it becomes easier to remember, so good luck Luke!