Meade Wedge experts help please?

[coldspace]

I have now mounted my LX scope onto a Milburn wedge for the first time tonight.

The wedge is set at 27.4 degrees for southern Brisbane, and the pier is mounted 11.5 degrees from magnetic south.

I leveled the fork arms, balance is pretty good on all axis, pointed the tube at the pole, turned on auto star, went to easy align, the scope went into some smart drive operation on the hand controller, then slewed to sigma octans region then ask me to center, I centred what I thought was Sigma, it then picked Canopus then slewed to it, I then centred canopus.

Alignment successful.

I then booted up the sky6, established a link, all good so far.

I know I am pretty close to polar alignment as I can keep a star in the centre field of a 9mm eyepiece for at least 5mins. After 15minutes it may have drifted about fifth field of view in the 9mm eyepiece.

I only need at the moment 1 minute accuracy anyway as I image with a Mallincam video system which only goes upto 1 minute, but down the track I may dive more into longrer exposure stuff.

Now to my problem,

I can't get my goto accuracy working on the wedge, it was perfect in the Alt/AZ mode all year but now its off by say 2 finder scope field of view from one side of the sky to the other.

If I stay in the same region of sky and hop from one object to the next then the goto accuracy is OK, and the scope stays tracking good.

If I then slew to another further region of sky then the goto is out, I have to adjust th hand controller, then sync the object on the sky6 and then it stays there.

Are my drives out?
or am probally doing something very wrong or do I need to get my polar alignment alot better.

See I like viewing lots of things around the sky with friends and the Mallincam video so I need better goto accuracy like I had when it was in ALT/AZ mode.

I thought once the scope was aligned up and if you Sync onto a few different objects around the sky this improves the pointing accuracy like it does in ALT/AZ mode, maybe it doesn't do this in Polar mode.

Cheers for feedback,

Matt.

[AstroJunk (Jonathan)]

Matt,

I'll tell you more next week when I finally set mine up!

But in the meantime, try a three star align as even very small errors in the sigma octans alignment which is very easy to do without a reticle eyepiece equate to big errors elsewhere.

Also a 'train drives' never goes amiss with a Meade

[coldspace]

Cheers mate,

I'll try the 3 star alignment tommorow night if its clear.

It was a bit of a rush tonight, the easy align is probally not the best.
I'll give the drives a train as well.

Matt.

[AndrewJ]

Gday Matt

If you did an "Easy Align" in Polar, it actually invokes the Polar One star align. As such, there is no "misalignment matrix" created for gotos, and hence the accuracy of all gotos depends on the accuracy of your wedge, and the orthogonality of your forks.
Now re the first, you noted

I centred what I thought was Sigma

Did you follow the instructions EXACTLY???? ( I hope not )
Ie did you use the wedge controls to centre it????
If so, you have probably screwed up your alignment
The Meade One Star routine "assumes" everything associated with the "scope" is perfect at start ( ie its at perfect HA=0 and the OTA is at "perfect" 90deg ) and that all errors are due to the wedge.
It then uses this "assumed" start posn to slew to where it thinks Sig Oct is, and asks you to adjust the wedge to centre it
( as it has to be the wedge in error, right )

If you have drift aligned the scope first, you "know" the RA axis is pointing at the pole, so the error is probably really associated with the scope.
In this case, ie you are happy the scope is well drift aligned first, you still do a one star align, but when prompted to centre Sig Oct, you just hit enter, dont even bother to look.
Centre the second star when requested and you will be away.

Andrew

[GrampianStars (Rob)]

Originally Posted by coldspace

I have now mounted my LX scope onto a Milburn wedge for the first time tonight.
......
I leveled the fork arms, balance is pretty good on all axis, pointed the tube at the pole, turned on auto star, went to easy align, the scope went into some smart drive operation on the hand controller, .....
I know I am pretty close to polar alignment as I can keep a star in the centre field of a 9mm eyepiece for at least 5mins. After 15minutes it may have drifted about fifth field of view in the 9mm eyepiece.
.....
I can't get my goto accuracy working on the wedge, .......

Matt....You MUST have RA Pec = ON to stop the slew at startup
Here's my proceedure which will fix your woes

[Barrykgerdes]

Polar alignment of the LX200 on a wedge can be time consuming and frustrating job.

The first and most important task is to find the exact 90 degree position of the OTA. Without this you can chase your tail all night.

This is the procedure I would use for a first effort:- Do a drift alignment to get the the wedge azimuth correct

Next set the OTA to the exact 90 degree position established previously.
Re start the telescope from the position of OTA at 90 degree. forks down horizontal and Finderscope underside.

Let the scope slew to Sgma Octans. AT THIS STAGE do not adjust the wedge azimuth. the best position was already found with the drift alignment. Just adjust the altitude to get Sigma Octans in the eyepiece centered in the vertical plane only.

Slew to the alignment star and bring it to the centre with the slewing contro.ls. If you only need to use the east/west you are probably pretty close to aligned. Re check everything again and you should be in business.

I had my LX200 on a permanent wedge and could never get Sigma Octans in the centre although my wedge was within an arc minute of correct and the gotos within two arc minutes always.

Barry

[coldspace]

Thanks for all your replies everyone.

Some more info for me to absorb.

I will try these tips and should be in buisness soon.
Once you know, you know.

Pity its full cloud up here ATM.

Matt.

[coldspace]

Originally Posted by GrampianStars

Matt....You MUST have RA Pec = ON to stop the slew at startup
Here's my proceedure which will fix your woes

Awsome write up mate.
I will turn the PEC on as well.

Cheers for your help everyone.

[Barrykgerdes]

The slew on start up is of no consequence as long as you do not move the scope back to the start position. The pulses are counted and automaticly compensated for.

Barry

[AndrewJ]

Gday Bazza

Re

Let the scope slew to Sigma Octans. AT THIS STAGE do not adjust the wedge azimuth. the best position was already found with the drift alignment. Just adjust the altitude to get Sigma Octans in the eyepiece centered in the vertical plane only.

This incorrect if you have properly drift aligned.
Ie If you have correctly drift aligned, the RA axis is pointing at the pole.

Thus, on the first slew, ( of a polar one star), you DO NOT adjust the wedge at all, in any axis.
You just hit enter and centre the second star. PoP.
Also, if you have correctly drift aligned, you dont need to be at perfect HA=0 and DEC = -90 at the start, you can be off by a few degrees either way with utter impunity. As long as you just ignore the eyepiece on the first slew to Sig Oct ( and just hit enter ), then correctly centre the second star,
all will be well

Andrew
( close yr eyes and trust the force )

[AstroJunk (Jonathan)]

Originally Posted by coldspace

Awsome write up mate.
I will turn the PEC on as well.

Seconded! thanks

[Barrykgerdes]

Originally Posted by AndrewJ

Gday Bazza

Re


This incorrect if you have properly drift aligned.
Ie If you have correctly drift aligned, the RA axis is pointing at the pole.

Thus, on the first slew, ( of a polar one star), you DO NOT adjust the wedge at all, in any axis.
You just hit enter and centre the second star. PoP.
Also, if you have correctly drift aligned, you dont need to be at perfect HA=0 and DEC = -90 at the start, you can be off by a few degrees either way with utter impunity. As long as you just ignore the eyepiece on the first slew to Sig Oct ( and just hit enter ), then correctly centre the second star,
all will be well

Andrew
( close yr eyes and trust the force )

Hi Andrew

Yes if you have done a full drift alignment you won't need to do any more. The trouble is most only do the first part of a drift alignment on a star near the meridian which will get the azimuth right then try to do an alignment according to the manual that calls for centering Sigma Octans with the wedge which of course will upset the drift alignment. I was just trying to emphasise that you don't need to adjust the wedge again on Sigma Octans which so many try to do. Just accept it and go to the main alignment star.

I always used my own mehod for a polar alignment. I first established that the orthogonality was correct then found the true 90 deg. point of the OTA and used a keyed dec scale with a vernier readout that allowed reseting to about two arc minutes. These items are established before going into the field.

I did an alti/azm two star alignmnent to accurately find a landmark on horizon at true south. I also know the star patterns around the south pole and how they look in a 26mm eyepiece.

I could then put the scope on the wedge and look at the landmark and adjust the wedge azimuth through the OTA and then with the OTA at 90 deg adjust the Altitude till I coud see the star pattern, do a fine adjustment on alt/azm and 90 deg using the known pattern to put the wedge in polar alignment within an arc minute.

Baz
.