SkyWatcher SynScan GOTO - what the Manual doesn't tell you!

[SkySpy]

This is a long term thread so apologies if this has been answered before, but I would like to know just how accurate can you expect a GOTO command to be, even if you get absolutely everything right (rare!).

I have a Celestron Nexstar 127SLT scope and I have been sacrificing productive observing time to test the actual accuracy I could achieve.   I have a StarGPS unit which auto updates the controller with 

bang on accurate date/time and location in the correct format, I use complete 360 degree precision leveling setup for the tripod, and I use a 20mm 70 deg FOV illuminated reticle for alignment.   

According to Stellarium my 70 degree FOV reticle should give an approximately 1 degree FOV in the eyepiece.  Using the illuminated reticle as a guide, the best accuracy I have been able to achieve (so far!)

is about 0.5 degrees of arc (i.e the target object is that far from the center of the eyepiece after slewing).  

0.5 degrees on my scope means using anything smaller than about a 12mm eyepiece and the object would be completely outside the field of view.  

Now the question is... is that acceptable or realistic?   Just how GOTO is well... GOTO?!!!

The manufacturers of GOTO scopes seem conveniently to give "no comment" on this... so I wonder what kind of real world accuracy other people are getting. 

SkySpy

[jambouk]

Half a degree is reasonable, but I've had it tighter.

This mount is the most basic of GOTO mounts out there, and is relatively "cheap" so one is unlikely to be getting bang on GOTO accuracy; even with an HEQ5 or NEQ6 equatorial mounts people can be happy with half a degree accuracy.

The GOTO accuracy depends on just SOOOOO many things. All of which much be summarised in this thread - be worth taking the time to read the whole thread.

Is there much slop in either axis? If so, tighten the nuts (I'm sure discussed earlier in the thread).

Level the tripod before attaching the mount head.

Can you add stability to the tripod?

Ensure power supply is sound and constant.

Is the scope balanced as well as possible.

Try centring your alignment stars with the reticle eyepiece, then if you have one put a barlow on the reticle and centre again before accepting (effectivly turing the 20mm EP into a 10mm EP with a 2x Barlow); if you had a 12mm reticle EP I'd still add the Barlow and centre with effectively a 6mm EP.

Always end your mount adjustments using just the up and right arrows.

Do a two star alignment rather than one / brightest star.

Do not touch the tripod once the start alignment process has started or finished... 

There will be other things people advise, but I think these are the most important.

In my opinion, a GPS device is unnecessary as it is pretty easy to input the date and time (and doesn't matter greatly if these are out by an hour or so, or a day or so (the commonest error is to forget to enter the date in the American format)), and the precise latitude and longitude is equally unimportant (being up to a couple of degrees out in latitude or longitude makes little difference).

Keep at it, it will get easier and your accuracy will get better, but I think half a degree out is acceptible. If the object is likely to be out of the FoV with the 12mm EP, then I would use a lower power EP first when you've GOTO'd, re-cente, then swap for the higher mag EP, and use the PAE function to update the GOTO for that constellation.

Good luck.

James

[trazor]

 I just sat down and read the instructions.

Wow that's outrageous, are you a real Astronomer..........  

[SkySpy]

Half a degree is reasonable, but I've had it tighter.

This mount is the most basic of GOTO mounts out there, and is relatively "cheap" so one is unlikely to be getting bang on GOTO accuracy; even with an HEQ5 or NEQ6 equatorial mounts people can be happy with half a degree accuracy.

The GOTO accuracy depends on just SOOOOO many things. All of which much be summarised in this thread - be worth taking the time to read the whole thread.

Is there much slop in either axis? If so, tighten the nuts (I'm sure discussed earlier in the thread).

Level the tripod before attaching the mount head.

Can you add stability to the tripod?

Ensure power supply is sound and constant.

Is the scope balanced as well as possible.

Try centring your alignment stars with the reticle eyepiece, then if you have one put a barlow on the reticle and centre again before accepting (effectivly turing the 20mm EP into a 10mm EP with a 2x Barlow); if you had a 12mm reticle EP I'd still add the Barlow and centre with effectively a 6mm EP.

Always end your mount adjustments using just the up and right arrows.

Do a two star alignment rather than one / brightest star.

Do not touch the tripod once the start alignment process has started or finished... 

There will be other things people advise, but I think these are the most important.

In my opinion, a GPS device is unnecessary as it is pretty easy to input the date and time (and doesn't matter greatly if these are out by an hour or so, or a day or so (the commonest error is to forget to enter the date in the American format)), and the precise latitude and longitude is equally unimportant (being up to a couple of degrees out in latitude or longitude makes little difference).

Keep at it, it will get easier and your accuracy will get better, but I think half a degree out is acceptible. If the object is likely to be out of the FoV with the 12mm EP, then I would use a lower power EP first when you've GOTO'd, re-cente, then swap for the higher mag EP, and use the PAE function to update the GOTO for that constellation.

Good luck.

James

James. Thanks  

All good feedback and advice.  I am doing most of what you suggest although I had not thought to add my Barlow to the reticule for even greater accuracy.

(Seems obvious now really!)

Also I have only recently learned about the wisdom of using the UP / RIGHT arrow approach for final adjustments.

Its a bit of a relief to know that my accuracy so far is sort of o.k, as with no benchmark I thought I was just missing something obvious, but it sounds from what you say that better results are merely down to greater refinement of set up and also (by inference) that given the nature of the tripod that anything better than half a degree and I haven't got too much to complain about!

One other thing I might mention here however is that when I command the telescope to slew to any object after alignment, I notice that the scope continues to refine it position for anything up to a minute before it finally settles on its fix.  The motion in the 20mm EP is so slow and gradual that I only noticed it with reference to the illuminated reticle but I have timed it over and over and it definitely continues to position itself long after I thought the scope was stopped. 

What is curious is that I have not heard anyone else mention this delay is final positioning so I even sent a query to Celestron themselves to ask if this was normal. (I am awaiting a response as yet).

SkySpy

SkySpy

[jambouk]

It does take some time to refine the position, but not 60 seconds.

Maybe collect some data on this, say measure the total time it takes to slew using GOTO from Deneb to Vega, repeat the test 10 times and see if it consistently takes the same length of time; then repeat for two stars further apart in bother RA and Dec, say Vega and Spica, and Vega and Castor. See if one axis is likely causing the problem. It may be that it just seems slow, but is normal. But without knowing the time it takes, it is difficult to comment on if this is abnormal; I can test it against my Skywatcher version once you have the data.

Again, it is undertaking a reasonably precise movement, and I am not an engineer, but for a £150 mount to be able to GOTO an object amongst a 42000 item database with an accuracy of under 30arcminutes and to be able to track it at sidereal rate... I think that is quite impressive, even if it does take 30 seconds to decide exactly where it thinks the object should be.

Get back to us with some data - maybe start a new thread as this is a bit off topic now.

James

[SkySpy]

It does take some time to refine the position, but not 60 seconds.

Maybe collect some data on this, say measure the total time it takes to slew using GOTO from Deneb to Vega, repeat the test 10 times and see if it consistently takes the same length of time; then repeat for two stars further apart in bother RA and Dec, say Vega and Spica, and Vega and Castor. See if one axis is likely causing the problem. It may be that it just seems slow, but is normal. But without knowing the time it takes, it is difficult to comment on if this is abnormal; I can test it against my Skywatcher version once you have the data.

Again, it is undertaking a reasonably precise movement, and I am not an engineer, but for a £150 mount to be able to GOTO an object amongst a 42000 item database with an accuracy of under 30arcminutes and to be able to track it at sidereal rate... I think that is quite impressive, even if it does take 30 seconds to decide exactly where it thinks the object should be.

Get back to us with some data - maybe start a new thread as this is a bit off topic now.

James

Strangely enough it was calibrating between Deneb and Vega when I noticed the movement, but I was clicking time in my head using the old darkroom technique ("Kodak One..Kodak Two..etc) rather than

anything precise, but next time I will get the stopwatch out and also try a few wider spaced stars as you suggest.

If it merits it will post the results in a new thread and also feedback anything Celestron might comment on.  

SkySpy

[stargazerlily]

Hi Nigel,

Thanks for your very informative post  

Another point to add to your "make sure the mount is level" part ... ensure that the lever or catch on the extendible legs is fully closed to lock the legs in their extended position.  I had a situation recently when I didn't follow this simple rule.  One of the tri-pod legs started to shrink in size throwing the entire set up out of kilter.  For a moment I thought the leg was going under ground until I realised what was wrong.

Pete

[SkySpy]

With reference to my previous post regarding alignment accuracy I mentioned that I had contacted Celestron themselves for feedback.  They have replied albeit without commenting on my real query which was to do with the time taken to do a slow motion adjustment at the end of a slew... however what information I have received has somewhat surprised me and I thought worth repeating here.   Celestron mentioned whether I had "started at the index point", to which I replied I did not know what an "index point" was!  The reply came:

The index mark is a starting position for alignment.  On the SLT it's not clearly marked, but it's when the optical tube is pointed at the horizon, so the telescope is flat and parallel with the ground.  Each time you align the telescope, start from this position.  This is a step that's often overlooked but is essential for a successful alignment. 

...in addition, they go on to say:

With each star (..you align to), you want to center it in the finder scope and press enter.  Then, you'll notice the scope moves much slower.  This is so you can center the star in the eyepiece.  First, use a low powered eyepiece like a 25mm to center the star.  If you want to be precise, you can then remove the 25mm, and place a higher powered eyepiece like a 10mm, and then re-center the star.  When the star is centered to your liking, press ALIGN to lock on.  Make sure you repeat this step for each of the 3 alignment stars.

So to summarize.. I did not know that leveling the scope was as essential as leveling the tripod (why is it not highlighted in the manual I wonder!),  and in addition I had missed the significance of having the scope slow down when you press ENTER on the HC.   I assume both of these things will significantly aid accurate alignment, but have yet to test them out.

I am still non the wiser about the slow-mo adjustment time taken by the scope which occurs after ALIGN is pressed, but the fact that they did not mention the time involved I can only presume means there is nothing unusual in the scope taking 30 seconds or more to finally stop and get a fix.  I am still going to time this precisely at some point but again, I have not been able to yet.

Hope the information will help others working on improving their GOTO alignment accuracy 

SkySpy

 

[jambouk]

Levelling the tripod is one of the main pre-requisits for the Skywatcher Mount; it does mention this in the set up instructions (http://www.skywatcher.com/downloads/AZ80&114.pdf).

With regards starting from the "index point", this is something which isn't mentioned in the Skywatcher manual, but there appears to be some differences between Skywatcher and Celestron. The star alignment options in this Skywatcher mount are: Brightest star (one star) or two star alignment. The user has to slew the scope manually to the first star always, so in effect it makes no difference to the mount what the original starting point is. However, as part of my routine when I was using this mount, I used to start at the "index point" as I believed it made my whole alignment more accurate, though I never did any tests to check this.

Equally, with the Skywatcher kit, there is no option to centre the star in the finderscope first, then press enter, then centre in the main scope... The user is asked to centre the star and press enter once. I recommend to people centring the star with a low magnification eye piece first, then swap over to a higher magnification eyepiece and re-centre, and possible then put the high mag eye piece in a barlow and re-centre THEN press enter. Again, always ending the centring with an up and right key stroke.

James

[jambouk]

A friend was asking me why there was no setting circle on the azimuth axis of this mount; I have no idea, but it would be helpful if one doesn't know the sky as it could be used to help with star alignment. Anyway, I found this really useful link on the net:

https://kenallen1976.wordpress.com/tag/alt-az-telescope-azimuth-ring-home-made-skywatcher/

James

[Coastliner]

My first scope, two years ago, was my Celestron 4SE, (altaz) and I have to say the alignment was extremely easy. I have just bought a Synscan mount and have definitely taken a step backwards as far as alignment is concerned.

With the Celestron you level the mount, give it the time/date and lat/long. Then, for planets, choose solar system align, point it at a planet, hit enter, done.

For other stuff, choose three star align, point to any three naked-eye stars (you don't need to know what they are called), done.

Simples.

[Quacker64]

May I ask what might seem a dumb question as a complete beginner as I am seriously considering the Skywatcher MAK 127 with the go to system (SKYMAX-127 SYNSCAN™ AZ GOTO) can the go to or auto feature not be disabled or over-ridden as I understand the scope is manually set up for 1st star alignment? Can the go to system not just be switched off and scope used manually?

I appreciate I might be over-simplifying a more complex issue.

[jambouk]

Yes, you don't have to align the scope or use the GOTO, and you can just manually slew to where ever you want in the sky. Depending on what part of the set up you do though, it might not even track an object when you find one, so you might be continually making corrections to keep the object of your desires within the field of view (and depending on the focal length of the scope (and if you are using a Barlow and/or high power eye piece)) you may be making a lot of corrections - in which case, why not just buy an unpowered alt-ax mount?

James

[Coastliner]

May I ask what might seem a dumb question as a complete beginner as I am seriously considering the Skywatcher MAK 127 with the go to system (SKYMAX-127 SYNSCAN™ AZ GOTO) can the go to or auto feature not be disabled or over-ridden as I understand the scope is manually set up for 1st star alignment? Can the go to system not just be switched off and scope used manually?

I appreciate I might be over-simplifying a more complex issue.

For very rough and simple tracking I point the mount North-ish, slew to where I want to be then set the tracking rate to sidereal. Yes, you still have to make regular adjustments, but it's fine for a quick observe.

[Quacker64]

Yes, you don't have to align the scope or use the GOTO, and you can just manually slew to where ever you want in the sky. Depending on what part of the set up you do though, it might not even track an object when you find one, so you might be continually making corrections to keep the object of your desires within the field of view (and depending on the focal length of the scope (and if you are using a Barlow and/or high power eye piece)) you may be making a lot of corrections - in which case, why not just buy an unpowered alt-ax mount?

James

My question was merely whether it could be done as I note with interest debate rages whether the GOTO system is useful to beginners or not. As a beginner myself I wondered whether it was possible to override or use manually. As was possible with the first fully automatic or semi-automatic SLR cameras which had full manual override for the traditionalists.

On a personal level (i.e. Myself) it would be the first of several scopes as I would probably want different ones for different work from hone to mobile/portable. I don't mind the traditional type of scope and learning but have no problems with the technology either. Whichever oath I think will lead to some interesting experiences and learning.

[Kropster]

If in doubt, get a GOTO mount, then you have the option of using or not.

If you go for manual only you may be kicking yourself later.

[ronin]

May I ask what might seem a dumb question as a complete beginner as I am seriously considering the Skywatcher MAK 127 with the go to system (SKYMAX-127 SYNSCAN™ AZ GOTO) can the go to or auto feature not be disabled or over-ridden as I understand the scope is manually set up for 1st star alignment? Can the go to system not just be switched off and scope used manually?

I appreciate I might be over-simplifying a more complex issue.

It think that you need to some sort of basic alignment OR the scope has to start from a defined position.

On a Meade that start position is level and North, the better level and North then the better the tracking even with almost no alignment.

On the Synscan I am not aware of this defined start position. It may have one just not aware of one, although they have changed the firmware enough times, there may be one now. There was mention of a Polar Aligning which came, went and may have returned.

The problem is the scope needs some idea of where it is "now" pointing to.

Stars in the East rise vertically(ish) those in the South are traversing horizontally and those in the West are heading down vertically(ish), so an Alt/Az mount needs some idea concerning how much Alt and how much Az to apply.

If the scope thinks it is pointed South but it is actually East then it will track horizontally and the star will move more or less vertically. If you manually slew then the scope does receive information from the encoders in the mount to tell it how much it has moved and so where it should now be, but that is relative not absolute. Basically it would know that it has moved 90 degrees clockwise from where it started, however again it needs to know where it started. So there will have to be some sort of "alignment" even if minimal to determine this start position.

On the Meade you simply set it level and North as accurately as you can and as long as slews and points about the right direction you press the OK/Enter button and accept it regardless of centering any alignment star.  Everything then is based on the start being level and North, but that is the way to get it to track the Sun during daylight.

[jambouk]

So yes it can be done with this mount, but to honest this isn't an easy mount to do that with. If you want to use a mount in manual mode then I wouldn't plumb for this mount. If you want manual, I'd get an alt-az manual mount (then you don't have to learn about equatorial mounts). If you think you can master the night sky and equatorial mounts in one go (many have done) then get a manual equatorial mount. If you want to be able to use the mount as GOTO too, then I'd go for something like the EQ5 or above depending upon the weight of the scope you are using).

Personally I don't see a problem with starting out with GOTO. My knowledge of the night sky is pretty poor, mostly because I spend so few nights outside, not because I have GOTO. When I do set up, I just want to look or image things, not spend all of my 2-4 hours navigating and star hopping, which may appeal to some, but doesn't appeal to me.

Whatever you get, you will want to upgrade at some point.

James

[Quacker64]

So yes it can be done with this mount, but to honest this isn't an easy mount to do that with. If you want to use a mount in manual mode then I wouldn't plumb for this mount. If you want manual, I'd get an alt-az manual mount (then you don't have to learn about equatorial mounts). If you think you can master the night sky and equatorial mounts in one go (many have done) then get a manual equatorial mount. If you want to be able to use the mount as GOTO too, then I'd go for something like the EQ5 or above depending upon the weight of the scope you are using).

Personally I don't see a problem with starting out with GOTO. My knowledge of the night sky is pretty poor, mostly because I spend so few nights outside, not because I have GOTO. When I do set up, I just want to look or image things, not spend all of my 2-4 hours navigating and star hopping, which may appeal to some, but doesn't appeal to me.

Whatever you get, you will want to upgrade at some point.

James

I make you right James! Another hobby - birding saw me agonise over my first scope. I now have several (five) spotting scopes with eyepieces ranging from around 16x to 75x from handheld in the woods to observing eagles on Mull and several,in between. I'm mentally already planning my next scope but will not know exactly what until I get the first one. Talk of getting ahead on oneself!

Steve

[Ambledown]

Guys, I've just put my SkyWatcher goto 127 together, I read the instructions and thought "What the Hell" well almost that but after reading this and another post I've found some confidence, especially all the tips.

 

However a mate said download Skyscanlnit android app (not an apple fan ) it gives me an accurate data input to the handset with all the info and hey it worked.

 

Again I can't say thank you enough. Now to get it working in the dark.

[happy-kat]

Thought I would add that app to my tablet too, it's called "SynscanInit 2"

[DorsetBlue]

On 30/04/2016 at 21:36, happy-kat said:

Thought I would add that app to my tablet too, it's called "SynscanInit 2"

That app is certainly quicker than opening my clock app on the phone for the exact time - very useful.

After a few months with mixed results from my bitsa (made from bits from Astroboot) Alt-Az Synscan, I thought I would include the following:

1) Yes, level is very important but I have had good results from the built in spirit level.
2) As my mount did not come with a telescope, I was using my SW 130P (900FL) that came with my EQ2.  I think this scope is pushing this mount to its limits, mainly due to the length.  I have just tried my little SW100 Heritage reflector on it and it is much happier.
3) Make sure the alignment stars you use ARE actually those stars, even with a 25mm Plossl this isn't immediately obvious.  This was one problem I had last night *SLAPS FOREHEAD*.
4) My mount does not immediately start to track accurately on GOTO.  Last night, I had to "tinker" with the position on the handset for a little while before the tracking settled down each time (yes, this was some time after the confirmation BEEP).
5) My home position is indeed flat and North (although I am not sure if this is required or not).

Although I have a great urge for a Celestron Evolution, I think this mount will keep me going for a little while yet.

[wayland]

Hi. I have a 200p Go to Dob which worked fine. After revamping the custom base that it sits on ( remotely  operated system) I find that the Park position is no longer in the original orientation. Without going into too much details I have not touched the scope just the base it sits on. This base has locator cups cast into it which the scopes locators sit on (if you catch my drift). My problem is I dont seem to be able to reset the park position! A bit of a black art to me. Can anyone put me straight please (excuse the pun)

 

Wayland.

[Ceramus]

After many years of using non-GoTo scopes I got to know the sky fairly well, especially from spending endless hours working out the best star-hop to the desired DSO. Finally succumbed and  got a big GoTo dob and must say it makes a big difference. I can cover a lot more observing 'ground" ( no pun intended...) in one night and by using the 'park scope' function save time in starting my following night's session. It's worthwhile exploring all the functions available in the Syncscan. My version is the 4.37 

[Rick6511]

Deleted.

Edited October 5, 2017 by Rick6511
Deleting seemed to be the better option .