SynScan GOTO accuracy?

[Roy@Aldermaston]

Please bear with me, I'm probably missing something obvious here. Scope levelled, balanced and accurately polar aligned, then carefully set to home position. Coordinates, date and time set using mm/dd/yy format and at present daylight saving. Now here's what puzzles me: when I go to the first star, which the handset lists as Arcturus, the scope misses by a long way - completely outside the field of view by some distance. However, if I move the OTA to the first star and manually centre it in the eyepiece (push and pull the tube) and then use the handset controls for the second and third stars (in my case Alderamin and Capella) it locates them accurately and reports a successful alignment.

My question is why does the scope miss the first star by such a long way, and why bother setting the home position if the scope can't compute the position of the first star in relation to its home position?

I almost forgot to mention that if I use the handset controls to centre the first star instead of manual adjustments, the second and third stars are less accurately located and the alignment frequently fails.

Any thoughts would be welcome,

Roy

[ronin]

Few points:

When you say polar aligned do you mean to the polar axis or to polaris?

Would have thought that Home Position was something determined from and therefore after the alignment not before it. As in the scope has determined where it is so can now determine a "Home position".

What do you mean by a long way?

Oops, Sorry, I read the first line saying 4SE. Didn't see the bit about the NEQ6. Presume it is the NEQ6 that is giving the problem.

[RogerTheDodger]

I get the same thing on my HEQ5 with EQmod, I don't bother with home position just do the 1st star align and manually move to it - it's a lot quicker and you'll and up doing it anyway, it would be fine on a pier.

[Digz]

This is interesting, as the last few times I have used my scope I have told it I have not been starting from the park or home position and the first star alignment was way off. I put it down to me telling the mount it wasn't parked therefore it doesn't really 'know' where the first star would be and gives it a best guess based on your lat, long and date and time. I assume you are telling the handset you are starting from the home position when prompted?

Another thing that got me when I first started out was I managed to put my long and lat in the wrong way around which really threw the system! I assume you have everything entered correctly?

Im no whizz at maths or anything like that but I wonder what the order of error would be in locating the first star if your scope is not exactly set to the home position correctly, i.e. how much error would be introduced if it was a few mm out?

[Roy@Aldermaston]

I may be having problems with understanding the idea of a home position having moved from the 4SE ALT AZ to the equatorial mount. By polar align I mean set up using Polaris to point at the NCP. After that stage I set what I thought was home position, ie, weights down and facing north and OTA up. This is done following a tutorial (Dion's) on the Astronomyshed website using a spirit level on the RA and DEC axises. From there I run through the alignment procedure.

The scope is taken down after each setting, but placed in roughly the same position for the next session, but my handset doesn't give an option to select start from home position. After the software version display (3.27) and warning it runs through coordinates, date and time, and when confirmed it goes straight to select alignment options. The manual is next to useless, and if it wasn't for the help that I've had on this forum I'd be even more confused that at present.

[Glider]

No, Polaris does not point at the NCP.

Polaris goes in the small circle on the reticule of the polar scope.

[Glider]

My sequence is,

Turn mount on.

Go through process of entering, coords, date, time,etc.

Do not start alignment when prompted.

Instead do polar alignment.

Put mount back to start position.

Do 2 star alignment.

For imaging were I might only look at one object all night I do a 1 star alignment on a star near to the object.

If I'm observing and going to move around the sky I do a 2 star alignment, and some PAE during the session.

If you do a 3 star alignment then the handset computes some other metrics including cone error. I find that if this is out of limits then alignment fails because of this but the error in Goto is still not significant that it bother me for observing.

[Glider]

If your handset does not prompt you to start from home position when you powered on then when you finished your last session it is saying you did not park and save a home position.

[Roy@Aldermaston]

Obviously not explaining myself very well. I use the hour angle information from the handset to place the Polaris circle in its current position on the larger circle, then use the ALT and AZ knobs to centre it in the circle.

[Cornelius Varley]

I may be having problems with understanding the idea of a home position having moved from the 4SE ALT AZ to the equatorial mount. By polar align I mean set up using Polaris to point at the NCP. After that stage I set what I thought was home position, ie, weights down and facing north and OTA up. This is done following a tutorial (Dion's) on the Astronomyshed website using a spirit level on the RA and DEC axises. From there I run through the alignment procedure.

The scope is taken down after each setting, but placed in roughly the same position for the next session, but my handset doesn't give an option to select start from home position. After the software version display (3.27) and warning it runs through coordinates, date and time, and when confirmed it goes straight to select alignment options. The manual is next to useless, and if it wasn't for the help that I've had on this forum I'd be even more confused that at present.

The option for starting from the home position is available on the V3 handset if you "park" the mount at the end of a session. The "home" position can also be customised if the mount is permanently set up in an observatory and the telescope "parked" in a horizontal position, for example, to allow the roof to be closed. Generally the home position is counterweight pointing down and telescope pointing at NCP.

The accuracy of the first alignment star is usually off, based on the settings and the starting position of the telescope. The second and third stars alignment accuracy is dependant on the manual readjustment of the first star alignment. The handset then maps the model of the sky over the alignment points.

Peter

[Neil McRae]

Roy I have exactly the same "problem" with my synscan on en eq5 mount i.e. when you select the 1st alignment star the ota is "way off". Sorry I dont know the answer to our problem.

Neil

[Glider]

My first star can be out of the FOV if I'm using a 10mm EP, what EP are you using whilst aligning?

Also, don't forget you need to save a home position when you turn the mount off.

[Neil McRae]

Glider I use a 15mm ep at first but when I say way off I mean 20deg in az and 10 deg in alt like really way off. Neil

[Glider]

Ouch, that is off.

Ok, this seems to come up every month or so on the forum, so running through the most common problems that I can remember,

Date in wrong format, it's mm/dd/yyyy

Coordinates in reverse order.

Coordinates in wrong format (Deg/min/sec).

Daylight saving not set right, it's Yes at the moment.

No park/home position saved.

Park/home position not correct; weight down, OTA straight up.

Low battery/power.

Not polar aligned, or incorrectly aligned using polar scope.

EQ5 with motor kit fitted incorrectly so gearing is wrong.

Tripod not level.

Guiding/EQMOD already running in background and interfering with setup.

OTA/tube rings/dovetail bar not square or twisted in the mount fitting.

Actually, that last one can give you 10 degree error if you use the short Skywatcher dovetail.

[Neil McRae]

Glider

That is a brilliant list and I have done the following when setting out to observe.

North leg pointing North

Level the mount

Polar align i.e. polaris in little circle

OTA pointing at polaris

Set as Home position

weights down

Date, time with daylight saving set to yes, coords entered in correct manner etc

Battery fully charged (same with 240v adaptor)

No other guiding programme running

EQ5 came with gearing and motors so assume all ok

Long skywatcher dovetail bar is fitted.

I believe all fittings i.e. rings ota etc are fitted ok

So I am at a loss but will never give up. If and when I find an answer I will post it but I am sure as Roy mentioned we are not the only ones who have this problem.

As an off the cuff remark Celestron alignment is far easier than the syscan system i.e enter your coords etc and then line up any 3 bright stars (enough said).

Neil

[Roy@Aldermaston]

Wow, where to start,

I normally use the supplied 28mm eyepiece for alignment, giving approximately X36 magnification. It sounds as though having the first star off alignment is typical, but since the second and third stars are spot on and the alignment is successful its not so much a problem, more that I was curious about the reason.

Anyway, I clearly haven't understood the home and park side of the setup. I though that park was only used if the scope and mount were left in the same position between sessions, but mine is packed away after each session; so to record home, should I return the scope to the home position and select park before switching off, or will that be negated out by dismantling the scope and re-assembling it for the next session, since its not not precisely in the same position each time?

Sorry for the tiresome questions, but as I said before the manual is useless, it may as well be written in Swahili for all the help it is!

Roy

[Glider]

Do you mean,

...OTA pointing straight ahead

...weights down

...Set as Home position

The OTA won't actually be pointing at Polaris. Also, the pointing ahead and weights down bit are both part of the Home position definition.

I have a HEQ5 and a CG5-GT and must agree that the Celestron setup has a much better feel to it.

[Glider]

Roy, at the end of each session I also strip my system down, but before doing so I always Park the mount.

When you start your next session this prompts the handset to ask you to start from Park or not. I select yes, but when asked if I want to start alignment I then select no.

At this point I polar align which involves unlocking the mount clutches and moving it by hand (Important, don't use the hand controller buttons).

Once polar aligned I manually return the mount to the Park position, lock the clutches and then start the 2 star alignment process.

[valleyman]

Download this Polar finder

http://myastroimages.com/Polar_FinderScope_by_Jason_Dale/'

I always Park my scope when i finish, but then I always dismantle so when I fire it up again it is going to be out of alignment so i always do a 2 sta align.

always remember it is the tripod that need leveling not the mount. .

Make sure you have the scope balanced with all the extras you are going to use. ie: finder, EP, Camera etc.

Do the polar align and then switch the power on and do the 2 star.

Use your larget EP for intial align 30mm then a smaller one 15 for accurat centering

Works for me every time.

You must never use the hand control to polar align, Only the alt/az adjusters.

Remember you are aligning the mount, not the telescope

[Mr Spock]

I have NEQ6 and don't have these problems. I'll go through my setup sequence..

Put the tripod down with the head facing approx towards polaris (single tripod leg to the south).

Level tripod using bubble.

Rotate Dec. 90° to open up polar scope.

Rotate RA till constellations align.

Move adjustment bolts until Polaris is in the circle.

Move RA and Dec back to zero (weights pointing down, scope pointing north)

Turn mount on (note: I align the pole first cause the red light drowns everything...)

Go through the menu, including entering the date the wrong way round and 'Yes' for daylight saving.

Select either two or three star alignment and select the first star.

It's never more than a few degrees away at the first star, usually a small anount out at the second too, doesn't take much to centre each star. Once that's done it should be ok, however...

...after successful alignment last night, Saturn was a bit off. I centred it and pressed 'enter' for two seconds, that re-aligned the mount. All was good after that.

[Glider]

Mr Spock, I think on the new Skywatchers you can dim the polar scope if it is blinding you from the handcontroller menu. PAE is good for local correction of accuracy but doesn't correct the whole sky model.

Valleyman, Polarfinder is excellent, when I said don't move the mount using the hand controller that includes rotating the RA axis to line up the polarfinder clock position. You make a good point about the semantics, I'm being lax in saying mount and tripod almost interchangeably.

[Roy@Aldermaston]

Thanks for the helpful suggestions, I think that I can get my head around this now. Just one final question: how important is it to polar align the mount before switching on? I've always switch on first so that the polar scope reticule is illuminated.

Glider, you beat me to it; yes Synscan version 3 does have a dimmer for the polar scope, its under the setup menu anonymously named backlight LED. I keep mine set to 2% which seem to be the most comfortable.

Thanks again,

Roy

[malc-c]

I tend to do the following:

* Place the tripod level on the ground with the mount facing North

* Turn on the synscan unit and run through the initial settings for date, location etc. At the end the handset will give the position of Polaris as if viewed on a clock (eg 7:20)

* Release the clamps so the mount can move freely. Now rotate the DEC axis to open up the polar scope, and then rotate the RA axis until the bubble on the polar scope is in the position of where the hour hand would be as indicated by the handset (ie 7:20) then lock both clamps

* use the alt-az bolts to place Polaris in the bubble.

* release the clamps on both axis and set the mount back to the home position (weights down, OTA on and North/south axis)

* run through the alignment process (normally 2 stars)

Hope that helps

[Glider]

It's not important at all as long as you don't use the handset and motors to move the mount but do it all manually. The disadvantage is the polar scope illuminator won't be on.

Don't forget, you don't just use alt and azi to polar align. To polar align you will have to rotate RA then use alt and azi adjusters, on some mounts you also rotate DEC to expose the polar scope objective. You must move the RA and DEC only by hand, then put them back to the park position by hand.

There is no need to turn the mount on/off/on if you follow my scheme ^^^^^ though.

[Glider]

Spot on Malc assuming step 3 is done manually by releasing the clamps and not the motors.