Synscan "Alignment may be poor!" after 3-star alignment?

[Jannis]

Ok, so, i did a 3 star alignment here the other say. Unfortunally with a bit bad polar alignment, and therefor had to slew the scope quite a bit to find the alignment star.

Finally found them though, but after the 3rd star was aligned i got the message "Alignment may be poor!" followed by "alignment success!". Didn't notice any problems finding or tracking object other then usual.

Didn't find this message in the manual, and surprisingly very little on the internet also.

So, can anyone explain to me why this message came up? What does it mean, and what did i do wrong?

Polar aligned with scope at 45 degrees, then turned off scope, set it stright upwards at 0 degrees towards polaris, and turned on scope again before doing the 3-star alignment.

[Ben Ritchie]

What I do is let it slew to where it thinks the first alignment star is (it's usually some way out) then release the clutches and manually point the 'scope directly at the star. After that, tighten the clutches, make fine adjustments with the handset if necessary, and hit align.

After that the second and third slews are usually pretty good, even if polar alignment is a bit dodgy.

[Jannis]

Aha! Now i've learned something new then!

What i've always done is set slew rate high, liek 5-6 on handcontroller and move it to teh star, then choose 2nd star. Is it more acurate to moove the scope manually then to do this?

But still, i've only gotten this message once though, and always had to adjust it quite a lot to be spot on the alignment star.

[ollypenrice]

No, the point about Ben's point is that he does that first movement with the clutches released so the encoders, the things that tell the mount where it is pointing, remain where the first slew took them. If you use the motors you keep the clutches locked so you move the encoders as well as the scope and provoke a major recalculation in the mount. This may be what is inaccurate.

Olly

[Glider]

Someone posted an answer to a question like this last week. it was very interesting. I think it related to alignment on a CG5 mount.

I think the upshot was that a 3 star alignment includes a calculation of cone error and though the alignment succeeds if the cone error is large you get an additional warning.

Sorry that's a bit waffled but the post was very ineresting as it explained the difference between 1, 2 and 3 star alignments and some other stuff that I didn't know.

Have a search of SGL.

[Ben Ritchie]

No, the point about Ben's point is that he does that first movement with the clutches released so the encoders, the things that tell the mount where it is pointing, remain where the first slew took them. If you use the motors you keep the clutches locked so you move the encoders as well as the scope and provoke a major recalculation in the mount. This may be what is inaccurate.

I don't know for sure, but I think that the mount likes to believe it started in the correct counterweight-down position and doesn't like the major recalculation if the first slew is way out and you correct it with the motors (hence updating the encoders). The problem is that it's easy to be out by a few degrees in both axes when setting up - especially if, like my EQ6, the mount is quite stiff and doesn't naturally settle to counterweight shaft vertical - so it's not unusual for the first slew to be well off.

Anecdotally, before I learned the 'release clutches and manually recentre' trick (which I think was suggested by Olly previously) I used to have a lot of problems getting a successful 3-star align. Now it works every time.

[Jannis]

Yes, i've heard that too. Basically means there's no point in doing anything but a 2-star alignment if you're guiding at least, as the 3rd star is only to correct for the mounts gear, if i understood good?

But, still don't quiet understand why. As i've had much more poor alignment then this with no warning, and so far i've been doing at least 12-15 3-star alignments.

I don't really worry about this though, just wish the manual was more clear...

[Glider]

Here it is, Skylook123 posted this and I thought it interesting;

There are two answers, depending on your thoughts and intentions for the alignment.

First, if you use the ESC button multiple times you will get to the SETUP menu. Press enter, then scroll down through the choices until you get to Alignment (not Alignment Stars; that choice allows you to fiddle with how Synscan presents the alginment star menu), press Enter, and redo the star alignment. Whether you chose 1-, 2-, or 3-Star Alignment, SynScan will remember the previous alignment until you complete this alignment so that if you change your mind and use ESC to exit, you should still have your old alignment. In any event, this is how to redo an alignment if the results from the previous alignment are unsatisfactory.

But suppose you only want to enhance the alignment, not redo it? Synscan has an odd, quirky sort of adjustment called Pointing Alignment Enhancement, or PAE. This augments the previous alignment, but does NOT change the model of the sky. Synscan divides the sky into 88 zones. If you exercise PAE on an object, then any GOTO to a target within that zone will have an extra refinement made to it's pointing. The basic sky model from the initial alignment is not changed. So, for example, if you have done a 2-star alignment and then a GOTO to say, the Ring Nebula, and the GOTO does not place The Ring where you think it should, then you can recenter on The Ring and use the Utility menu, select PAE, and follow the instructions to accept the new location. From that point forward until you eitner delete all PAE with the Utility Menu, or until you redo a full alignment, the region around the physical sky where The Ring was when you used PAE will be adapted to your adjustment. If you then GOTO, say, The Swan in Sagittarius, Synscan will pay no attention to your previous PAE. If you like the results, fine; if you find the pointing to The Swan is also not to your liking, you can invoke PAE on this object. Then, GOTOs in that region (again, the actuall azimuth-elevation of the part of the sky where the object is at the moment) will be affected. Each PAE is independent, and only effective in a region around the invocation point. The purpose of PAE is to adjust the pointing for mechanical vagaries of the mount, such as less than perfect assembly, or looseness of some component(s), etc., that affect local pointing. PAE does not change the sky model developed in the alignment.

If you use a permanent setup, then over time, the entry of PAEs as you move around the sky (and note that PAE is not to an object, but to a region of your physical sky no matter what object is in that location), eventually you will have a refined space for your mount as long as you never redo an alignment of any kind. Once you redo an alignment, all PAE memory is erased. This includes power cycling effects; if you use Park before removing power, all alignment data is saved along with the PAE data. If power is removed without Park, all alignment data is lost. I wish Synscan had a feature to request alignment and PAE status to verify the condition, but we are blind to that.

If you relocate to a new site each night as I do (my Atlas is used for public outreaches at schools, parks, resorts, etc.), then PAE in the memory can provide mischief when doing the alignment on the next power up. It has saved the previous adjustments, so if you happen to choose an alignment star in a region where the previous use caused you to use a PAE, then the offset will be introduced to the pointing. You make your centering adjustment, then move on. But when your alignment process is complete, the PAE memory is erased. Oh, my, what a warped sky you might have! Luckily, all PAE can be erased without affecting the sky alignment data.

So, there you have it. Synscan does not have a feature to add stars to the alignment model as you go on after the alignment, but it does have PAE for local effects. But SCTs can play some mischief with this feature due to mirror "flop" when crossing the meridian, and mirror shift when changing focus. For serious pointing, such as for small CCD chips, then microfocus addons to the optical tube are almost essential to stop some of the mirror movements that can affect the alignment models or even PAEs.

[Skylook123]

I will add in reference to this thread, that, yes, Synscan's 3 star alignment is stated as a cone error correction; non-parallelism between the optical tube's axis when the mount is at DEC= 90, and the mount's RA pointing axis. I have often gotten worse performance with a 3-star than with a 2-star; 3-star worked great when I found I had a shim error on my attachment plate.

Regarding the odd 45 degree offset that Synta ships with, that, along with the North pin in the wrong hole for most latitudes, is a big personal annoyance with me. Many of us have slewed the mount in DEC until the polar scope path is opened, loosened the tiny grub screws just under the top puck at the dovetail, and rotated the top puck to align it, when the polar scope hole is opened, to DEC = 90. This then allows us to do an iterative polar alignment: set up as normal, good compass heading, level (very important for this method), accurate as possible latitude setting (the numbers on the side are, at best, rough guesses), and good Home position. More on that in a bit. Power up, do a 1-star alignment to a star more than 4 hours RA off Polaris, do a GOTO Polaris, notice the offset. Take out half of the offset with the mount mechanical (azimuth/latitude) adjustments. Check the polar scope for visibility (this is why to move the puck to align the dovetail slot with the open polar scope port). If it is there, and the too bright reticle is sure to let only Polaris burn through, then finish by putting Polaris onto the big circle in the clock position where the hand controller says the Polar HA is at that moment. If not, do another 1-star alignment, then GOTO Polaris and take out half the offset again. Usually, if Polaris now hits the inner ring of a Telrad, it will be in the polar scope. Check and finish. If you start level, with a good home position, and only take out half the error, then the 1-star iterative alignment will work usually in two steps. The error has a sign and trigonometry influence, so if you take out too much off the offset you might have entered another quadrant of the solution and you shall maneuver the old mount all around Polaris, never really getting it.

A hint about home position. I used to always be in a hurry to set up at my public presentations, and always was very disappointed. Now, I get there early enough to do the following to set up in the daylight/twilight. First, I level the tripod with a bullseye level. Yes, I know that for GEM mounts level should not be important. Let Mr. Synta's software know that, because it is diabolical on this). So, once level, install the mount head and tighten down. Install the counterweights. Don't forget; I did once, and the misbalance swung the OTA around and destroyed the controller caddy. OK, leveled, mount installed, CWs installed, verify the latitude setting with some sort of carpenter's protractor; I use a $7 inclinometer (measures wall angles) I purchased at a home building store. Add the OTA. Here is where the relocation of the puck serves another help. Loosen the RA clutch and pivot until the CW shaft is level, using our friend the bubble level. Lock the RA Clutch. Set the RA setting circle to a convenient number, like "0". Now go to the OTA. Move it in DEC, using the bubble level to sense when the OTA is perfectly level. Lock the DEC clutch. Set the DEC setting circle to the latitude (magic - DEc and Latitude both go from 90 at North to zero at the equator. What a handy tool!). Since the DEC setting circle has multiple ranges, be sure to choose the latitude that will allow it to roll to zero when you recover to be upright. So, now with 0 and latitude set in the setting circles with the CW shaft level and the OTA parallel to the ground, now roll the whole setup in RA to the starting position: RA should now be six hours different (Hopefully, "6" but might be "18", exactly) and lock the RA clutch. Move the OTA in DEC to setting circle is "0" and lock the clutch. Now you have a perfect home position IF you are: seriously retentive about leveling the tripod, setting the right latitude on the mount head, and getting a good CW level and DEC level. Well, just consider it an extended verification of balance.

It takes much, much longer to read than to do. My best time right now is about four minutes from tripod level to full home position setup. And I often hit the 1-star alignment within 2 degrees. Before, I would miss by 15. And on several occasions, the crowd was so eager to get started I only did a 1 star alignment and got every GOTO that night inside a 0.6 degree FOV eyepiece. On a 2-star, I often get dead centers. Final word of advice, no, your face is not perfect. Your nose can interfere and introduce parallax in the alignment eyepiece unless you use a reticle eyepiece to firm up the location of the guidance star. My eye doctor clued me on to this! She knows I do this astronomy thing, so she gave me the distance from my pupil opening to the side of the bridge of my nose. It was just a bit narrower than half the shell of my alignment eyepiece. Going to the reticle has really made alignments successful.

I hope this helps; some has come from six years experience with the Atlas, much has been guidance from the Yahoo! EQ6 Users Group, a gold mine of great help and reference.