Skywatcher Synscan 2 star align query.

[squeaky]

When setting up my scope (see my sig) I first find Polaris and centre it in my FOV - then drive the scope down with the down arrow until the OTA is level. Then I turn the power off.

This so that my scope is pointed North and is level as it says in my book that it should be before starting a 2 star alignment.

So now I power up and choose Polaris as my first alignment star.

Since I'll be doing imaging and the weight of my DSLR affects things I align Polaris in the centre of the graticule available via Backyard EOS. Since my FOV is approximately 20 arc minutes and I can use a five times zoom - it means that I can be very accurate here.

At the moment, at between 9 and 10 pm I use Altair as my second alignment star because it's pretty much due South and is a nice angle above the horizon.

All with me so far?

The query is this... after centring Altair in my finderscope because it's usually off target by around 1 deg AZ and about 2/3 deg ALT.... it drifts. A lot. It appears for all the world as if the scope is not tracking Altair at all. It drifts a fair amount in AZ and a smaller amount in Alt - going up and right. So I have to offset in my view continuously. I've tried doing this for five minutes and more in the hopes that it might be some sort of settling or backlash issue but it never does settle. So I have to offset it in such away that it will shortly drift over the exact centre of the graticule and then hit ENTER

After that I get the "Alignment successful" message and Altair will then "stay put" - albeit usually a little off centre. If I then target Altair as a "Named Star" it will re-centre reasonably close to where it was.

But is this apparent non-tracking drift of the second alignment star normal?

[squeaky]

EDIT: I picked an NGC in my North Western sky last night since it was the least affected area from the haze.

When targeted it showed up in my camera's FOV - about 9 arc mins high and about 7 arc mins right.

So I centred it and started imaging.

Here's the thing - if I was to sit and watch the sky as it rotated around the Celestrial North Pole; in the short term my target would appear to be moving down and right.

And that's EXACTLY what I'm seeing between images. Every image is about 2 to 3 "star diameters" down and right from the last one. So while alignment and targeting seem to be within reasonable bounds - it does look as though it's not tracking.

What do you think? Is this normal for this scope and mount?

[Mikea]

I don't have the same scope/mount, but I wonder about the merits of using Polaris as one of the alignment stars. Have you tried using a different pair of stars to see if you get the same effect?

[squeaky]

Not yet.

My sky viewing "corridor" is limited by my house and trees. Cloud dodging recently has made things harder. It just so happens that these two stars have been best sited and easiest to identify in the haze between them to pick from the list of stars offered by the alignment software.

It's obviously going to have to be something to try though!

The recommendation in the handbook is two stars at least 60 deg apart in AZ and of similar ALT. These two currently fit the bill. Finding two other stars that much apart in AZ and of similar ALT with my horizon constraints is no easy task. I need to learn my way around the sky better!

[devilgas]

not heard of the "drive the scope down until the OTA is level and reboot" thing before. i think that may be the main source of your problems.

the mount should be polar aligned using the polarscope and the ota roughly pointed at polaris. this should be the start position, not with the OTA parallel to the (flat) ground. you won't get the scope pointed directly at polaris as the counterweight bar should be in a vertical plane (you won't get it vertical with the scope pointing at polaris) as per the diagram on p5 of the manual (going by the PDF ).

i park my scope after every session, so the mount is 'pointing at polaris' on power down. to get the OTA pointing roughly to polaris, i loosen the 2 clutches and nudge the OTA to the correct position, then tighten the 2 clutches. at this point i power the mount up and go through the setup routine. doing this and a single star align close to the object i'm interested in, i can usually get 90-120s exposures through the camera with minimal trailing. the above with a 3 star align generally means i can slew the scope to anything in the sky with decent accuracy (it's rarely spot on, but still visible in the finderscope).

hth!

[devilgas]

sorry, just read you're sig and see you're using a dob. not sure if what i've written applies to them - probably not as i'm using an EQ5. sorry!!!

if using in Alt/Az then you will always get field rotation, but the tracking of the object should still be good.

[hemihaggis1]

skywatcher software does need the scope to be level before you start , it used to but the latest updates to firmware does away with that ,

do not use polaris as an alignment star , choose two different stars in different parts of the sky , polaris can be used as an alignment star by eq mounts , but that is a 1 star align , you center on polaris ,then the scope slews away and you re-center on polaris .. do not use it for two star aligning

[squeaky]

I'm essentially starting from a nominal parked position - horizontal and North.

I'm only using Polaris the first time to ensure that the scope is PARKED North.

THEN i turn the power OFF.

NOW... when I turn my power on I'm starting from scratch - haven't aligned on any stars... and the Synscan gives me Polaris as one of my optional alignment stars.

So I'll start again... does anyone with a DOBSONIAN see the second alignment star drifting in their field of view before they hit ENTER?

[Prador]

Your description of the initial alignment on Polaris (to align north) suggests you are centering the star itself and not the northern celestial pole.

Would this make a significant difference?

Everything I have read also suggests Polaris is a poor choice for a 2 star alignment. Is it possible to take the behemoth to a different spot to gain views of other alignment stars?

[squeaky]

THAT is a question that I have asked of OVL via my retailer.

Got the answer just one minute ago.

"Magnetic North" using the compass on my mount.

Yeah right. (WHAT compass?)

Told the young lady that they were misinformed and am waiting for an answer back.

My query was stated pretty much exactly as your question here.

As for moving the scope. I'd have to pack it all into my car, drive miles and miles, then assemble. This, for me, is VERY hard work and not undertaken lightly. I'm talking an hour to get the car loaded with frequent rests between each item lift to get it all in the car - about an hour's labour. Same when unpacking the car and setting up. By which time I'm pretty shattered. After viewing I have that entire routine to repeat in reverse. So I do as much of my practising as possible at home.

As for not using Polaris for alignment - I take your point for an equatorial - but mine is a DOB.... AND if it wasn't acceptable why would my Synscan offer it in the list of alignment stars?

I'm certainly going to be on the lookout for a different pair of alignment stars - but my last question still stands.

As of five minutes ago I may not get the chance to test all this for three or four months. (See my thread on stripping a Dob mount)

[russ.will]

I find the tracking on my 300p Synscan pretty good, but ONLY if the last adjustments made from the handset are in the direction the subject is travelling in. There are horrendous amounts of slack in the drive system of the Auto/Synscan Dobs, so if your last movements to centre the subject are in the opposite direction, it is literally minutes before the slack has been taken up by the motors driving in the opposite direction.

To explain further; If your subject is west of the meridian looking south, the subject will be moving right and down. Your last centring adjustments need to be right and down so the slack is already taken up. Looking south east requires right and up, etc.

That's the reverse of what you will see in the eyepiece/camera LCD and I suspect, on the screen of Backyard EOS, as the view is flipped left/right and up/down.

All that said, the tracking action is pretty coarse in it's steps and you'll suffer field rotation on exposures of much more than 30 seconds. It's one of the reasons I miss my HEQ5 Pro, even just for visual.

Russell

[russ.will]

Oh! I forgot to mention, that the base has to be absolutely level, as in spirit level andurge same spirit level to independently verify the tube is perfectly level before switch on.

For alignment, I tend to use two stars in broadly the direction I'm viewing in and at different levels. Altair and Arcturus if viewing broadly south for instance. If I shift to another area, I pick another two.

Russell

[russ.will]

"andurge" should read 'and the'. Chubby fingers + iPad = Sorry!

[squeaky]

Yep.

I find much the same thing.

One thing though... a lot of that slack may not be down to backlash on the gears - but you'd have to strip down the AZ assembly to be sure.

See this post

[brantuk]

Level the mount - switch on - enter date-time info in the correct format and then begin a 3 star align. Choose a wide spread triangle of stars in a quarter of the sky. Move manually to the first one and - center and register it. It will then "goto" the next star and ask you to center it. Finally it will "goto" the third one and register it (ie align).

Anywhere you goto in that local area of sky will be tracked pretty acurately - it'll stay in a 15mm eyepiece for at least half an hour before appearing to drift. If you goto somewhere outside that quarter of the sky it will be inacurate but close. Use PAE to register the offset. Do this half a dozen times across the sky and it will be acurate all over.

Don't use Polaris for an alignment star - this is only done to register the polar elevation from level when using the "Auto Tracking" handset (I.e. it sets your lattitude). Not necessary with the synscan goto handset. Follow the above method and it will "learn" it's accuracy from your use of PAE. I think you've been confusing the Auto instructions with the Syncan ones. Hope that helps

[brantuk]

Oh... Ive not used the backlash settings on mine - never had to - but backlash can be considerably reduced by finishing the first alignment star with a right movement, followed by an up movement in the east, or a down movement in the west, depending on where your first alignment object is. The rest is then down to the "Goto" and your use of PAE

[squeaky]

Level the mount - switch on - enter date-time info in the correct format and then begin a 3 star align. Choose a wide spread triangle of stars in a quarter of the sky. Move manually to the first one and - center and register it. It will then "goto" the next star and ask you to center it. Finally it will "goto" the third one and register it (ie align).

Anywhere you goto in that local area of sky will be tracked pretty acurately - it'll stay in a 15mm eyepiece for at least half an hour before appearing to drift. If you goto somewhere outside that quarter of the sky it will be inacurate but close. Use PAE to register the offset. Do this half a dozen times across the sky and it will be acurate all over.

Don't use Polaris for an alignment star - this is only done to register the polar elevation from level when using the "Auto Tracking" handset (I.e. it sets your lattitude). Not necessary with the synscan goto handset. Follow the above method and it will "learn" it's accuracy from your use of PAE. I think you've been confusing the Auto instructions with the Syncan ones. Hope that helps

NOPE !!!!!

That is all true, I'm sure, for an equatorial. But mine is a Dobsonian.

The set up routine AND the Synscan software are different.

There's no such thing as three star align available for my scope. Brightest star and Two Star Align ONLY.

Nor is there any Polar Alignment.

The only "alignment" done for the dob is to have the OTA horizontal and pointing North.

[squeaky]

Oh... Ive not used the backlash settings on mine - never had to - but backlash can be considerably reduced by finishing the first alignment star with a right movement, followed by an up movement in the east, or a down movement in the west, depending on where your first alignment object is. The rest is then down to the "Goto" and your use of PAE

I think that might be where I was going wrong. The book says to always finish going up and right. But, as you say, if your target is moving otherwise - then that's the way you should finish.

I "think"

There's no way I'm going to be waiting 3-4 months for a new top base board, so I've been baking mine dry in the back bedroom and the Central Heating on for that room set to max.

Then I got my trusty router out and set it to a featherlight touch on a flat area well away from the blown stuff. Then worked my way onto the bad bits and went over and over it until I got no more sawdust. Then I applied a very thin film of varnish - wiped it on and wiped it off - so that it will dry well before the dampness of the varnish has time to blow the chipboard again. Just about to do a repeat coat to help seal it up. Tomorrow I'll reassemble and see how it goes.

[brantuk]

I don't believe I mentioned Polar alignment - I was talking about the difference setting lattitude on the Auto handset - mines a Dob as well - it's an Auto upgrade to Synscan Goto and I know the routine extremely well. You should have the AZ Synscan Goto handset which does have a 3-star align routine and doesn't need the lattitude setting because you enter it in the date-time info. I believe you've misread my advice but it's up to you if you take it or not.

I also have an NEQ6 pro with the equatorial Synscan Goto handset and I'm very familiar with both mounts and handsets. Try it - you may surprise yourself.

[squeaky]

Now I'm getting confused. It's been a long day. Sorry.

Whichever one is the all singing all dancing version that costs a fortune is the one I have.

But there's no such thing as a three star align available in my alignment options. The only place I've seen three star align as an option is for the equatorial version of the software.

I will be trying to sort out two suitable alignment stars that don't include Polaris - but I'd still like to know why on Earth (or in space) the Synscan offers Polaris as one of the Two Star Alignment options if it's not suitable?

[squeaky]

I've just checked. I have the GOTO.

So should I have a Three Star Align available in my handset?

This where I've been getting confused. We appear to have the same telescope - but my set up routine just plain isn't the same as yours.

[squeaky]

More checking.

My handset says that I have version 3.08

Skywatcher's page here: http://www.skywatcher.com/swtinc/customer_support.php?class1=1&class2=110

Says that 3.08 is the latest version.

[brantuk]

Sorry Squeaky - you're right - I double checked myself and realised when I posted I was reading from the wrong manual. The AZ Synscan Goto doesn't have 3-star align - just Brightest star and Two Star align. Three Star is in the EQ manual so please accept my apologies for confusing you.

Unfortunately I can't edit posts for some reason so my mistake is there for all to see lol (d'ohhh). Anyway - stick to a quarter of the sky as I mentioned and the "finishing" movements as described and two star align will still do the biz for you. Use the PAE (on either handsets) to refine accuracy when moving to other parts of the sky. It will track an object for a good 30 mins before drift sets in.

[Paulb3098]

Hi,

I have the 250px goto and this set up works for me:

1. Make sure it's on flat ground

2. Turn on and enter data, time and location etc

3. Select two star alignment, this is my best choice as I have limited views and I normally find the 2nd star is out of view

4. Select a star and use the finder to get the star into view - either manually or by nudging the handset

5. Use my a 16mm or 24mm ep to centre the star, reduce to a 6.4mm to get it right in the centre - this really helps the goto to get things in the FOV when viewing later

6. Choose the second star (I have attached the list and charts for the 3.08 version), it's rarely in the FOV so I need to nudge the scope.

7. Repeat steps 4 and 5

8. Start viewing

Hope this helps, good viewing.

Paul

SkyScan_Alignment_Stars.pdf

[Capricorn]

Being about a degree wrong would make sense, that is the difference between Polaris and the earths axis. Which since you appear to not be using a polar scope would match up.

Alignment using Polaris is never a good idea, something up there is taken a "0" and Polaris is usually it, any division by 0 in whatever algorithm used causes problems. Usually manufacturers advise against it and I am surprised that Skywatcher do not.

Forget using a compass.

The whole setup sounds as if it is intended for visual and for visual I would expect some drift. It just does not tend to be rigorous enough, mainly because it doesn't matter as much. And you may not like it but you have a classic visual system - large, heavy Alt/Az dobsonian mounted scope.

When using an equitorial mount the set up for imaging is quite time consuming. Then do not expect an exposure time of more then 60 seconds before drift takes effect. Using an Alt/Az based mount the effect has to be worse as you will have field rotation included in the mix.

Another point is that goto is used to locate an object, expect to have to centre anything once it is located. To track accurately imagers use a guide scope and system. If goto was good enough they would not spend the money on a second scope, camera and laptop after all.

The 300P is certainly not lightweight, drive accuracy has to be a problem, simply too much weight for the drive train to accurately control. You cannot alter the balance either and what the balance set up for a visual dobsonian will be different to that for imaging. The 300P will also have a reasonable focal length, (NOT f number) and the longer that gets the greater any tracking errors are amplified. Imagers use short focal length scopes for a reason.