Polarscope Optical alignment on AZ-EQ6-GT

[Mark_C]

I have recently bought an AZ-EQ6 and have gone through the process of aligning the polar scope reticule with the RA axis of the scope. The reticule crosshair now remains central whilst rotating the mount on the RA axis, however I've noticed the actual image does not rotate concentrically, i.e it looks off axis when rotated 360 degrees.

I am sure read that the optical axis of the polarscope is aligned at factory and that it can't be adjusted, in which case, someone must have been drunk when they were aligning this particular scope!

Is it normal for this to occur and if not, is there any way to align the optics myself?

[Owmuchonomy]

Can you explain what you mean when you refer to 'actual image'? I'm not sure I follow otherwise.

[Mark_C]

Sorry, I'll admit that I'm not that great at explaining things like this!

Basically, as I rotate the mount and look through the polar scope at a distant object, everything I see does not rotate concentrically, i.e it seems off be off axis and wobbles. I always thought the polar scope was optically aligned with the RA axis of the mount, however it seems mine isn't. 

[msh1]

you need to put a star or something right in the centre of the cross hairs and rotate the mount if it stays in the centre then its aligned if not you need to use the allen key to recentre the reticule 

[Mark_C]

This is extremely difficult to explain without a pictorial demonstration of the problem.

I'm pretty certain the reticule alignment isn't the problem, it appears to be the optical alignment of the polarscope relative to the RA axis that is the issue. I've already adjusted the calibration screws to allow the crosshairs stay centred on the object when the RA axis is rotated. The problem is that the entire FOV (including the reticule) does not rotate evenly. Does that make sense?

[hobsey]

Hi, Mark.

I think I know what you mean as I had the same thing with my polar scope.

Its as if the polar scope isn't in straight or something else isn't aligned correctly. When you turn the RA, the reticule isn't going in a perfect circle. Instead it goes off to one side on a different axis when turned.

Does that sound about right?

[Mark_C]

Hi, Mark.

I think I know what you mean as I had the same thing with my polar scope.

Its as if the polar scope isn't in straight or something else isn't aligned correctly. When you turn the RA, the reticule isn't going in a perfect circle. Instead it goes off to one side on a different axis when turned.

Does that sound about right?

Anthony,

Yes that's exactly the issue!

I thought it was just me at error to begin with but then I realised after much adjustment of the reticule that the whole FOV would continue to shift.

Did you manage to solve the issue in the end?

[hobsey]

I got it aligned as close as I possibly could which isn't far off being spot on as I started to loose the will to live.

I haven't tried it out yet to see how accurate it is but I will also be doing a polar alignment through the handset when it comes to it.

[Alien 13]

I had a similar problem with my EQ3-2 polarscope but there are some adjustments on that one you can make to the position of the barrel by another 3 screws.

Alan

[Mark_C]

I think the issue is that the bore hole for the polar scope is not in alignment with the RA axis of the mount. I have no idea whether this has an effect on the accuracy of the polar alignment though.

I've managed to capture a video to demonstrate the issue, it's not the best but it does show the issue. The crosshair stays (mostly!) at the centre of the intended target - the tv aerial. My concern is that polaris will change position when the mount has to be rotated in to the correct position, surely this will cause alignment issues?

Here is the video:

[wxsatuser]

My HEQ5 is the same but worse........don't worry about it.

Just get it aligned, I used a tv aerial a short distance away, like in the Astronomy shed videos.

[Dave_D]

mine does it too but i only use the polar scope for rough alignment and then use alignmaster

[Mark_C]

mine does it too but i only use the polar scope for rough alignment and then use alignmaster

I'll take a look at Alignmaster, it looks a very good piece of software, very easy to use.

[hobsey]

Just watched your video, that is pretty much as close as I got my alignment.

As soon as you described it first time round I knew exactly what you were talking about.

[jambouk]

Mine does the same thing; but i think mine is worse. Mine ends up perfect at the start and the end of the 180degree rotation, but the target drifts off the cross hairs half way through.

I'm only doing solar system imaging at present but the PA seems pretty good.

Jd

[Ouroboros]

Looking at the video would I be right in thinking that although your polar scope is parallel with the RA axis of the mount, it is positionally offset from the axis? If so I would think you don't have anything to worry about. I have to say that I can't recall noticing the effect you're seeing to the same extent on my AZ-EQ6. But I will check sometime in the next day or two .... It if stops raining that is.

[Ouroboros]

OK. I've checked my AZ-EQ6 and I do not see the effect you see. The image of the scene rotates concentrically, to use your words.

If it were me I would not be happy with your mount. Technically it may well not matter, but I reckon if you've paid 1300 quid for a piece of kit it should be right. Just my view.

[Mark_C]

OK. I've checked my AZ-EQ6 and I do not see the effect you see. The image of the scene rotates concentrically, to use your words.

If it were me I would not be happy with your mount. Technically it may well not matter, but I reckon if you've paid 1300 quid for a piece of kit it should be right. Just my view.

Unfortunately, the mount was bought used so there is no comeback. :-( It is one of those things that you tend not check for as you assume it will be fine. I imagine the PA will be slightly out due to the wobble as Polaris during RA shift, by how much is difficult to tell. I suppose if it gets me rough alignment, I can use the built in handset polar alignment feature to increase alignment accuracy, or use Alignmaster. Unfortunately it has been cloudy here pretty much every day since I bought the mount, so have no way to test. :-(

[Mark_C]

Hello all,

I thought I would follow up on this thread with new info. I emailed the guys at skywatcher.ca at the beginning of the month (took them 3 and a half bad weeks to reply!) and here's what I got as a response to my observations above.

 

"Dear Mark, 

 

Thank you for choosing Sky-Watcher. 

The polar scope’s optical axis does not need to be perfect parallel with the RA axis of an EQ mount for polar alignment. 

Slightly off axis will not impact polar alignment, if the reticle in the polar scope’s FOV has been properly aligned as shown in the video."

 

 

 

So there we have it from the horses mouth. It seems that regardless of how much the image wobbles, as long as the reticule is centred within the polar scope then polar alignment shouldn't be affected.

[neil groves]

I just posted a thread about this very issue, I have focused on a brick on a chimney, the brick in question stays on the crosshairs yet the image seems to 'move' as I rotate the mount RA 180 degrees.....clear skies for me tonight so i'm going to try it out with some 1 -2 minute subs and see what happens.....

Neil.

[neil groves]

made no difference whatsoever......have to investigate further

Neil.

[wxsatuser]

made no difference whatsoever......have to investigate further

Neil.

As well as aligning the reticule you still need to nail the polar alignment.

Even though my PA is about as good as it gets, unguided is rather poor, I don't see

much more than 60secs without detecting trials, I don't run without guiding.

If you want to see visually how good you alignment is, the DARV method will show you in about 5minutes.

Here is a star just East of the meridian and near the celestial equator, the nearer the better but don't get OCD about it.

This is for the azimuth adjustment on a GEM.

This is a 3minute DARV each way with the slowest speed in EQMOD.

See the out and in legs overlap, this is near perfect.

Here is a star to the East about 20degrees above the horizon near the celestial equator, again no OCD on this.

This is for the altitude adjustment on a GEM.

The DARV here is 3minutes each way, this time you will notice that the return leg is just starting to drift.

These two DARVs were completed in less than 15minutes, they can be cutdown to about a minute each way

but there will be a loss in accuracy, three minutes each way seems a good compromise and I easily get 10minute subs.

[jambouk]

Mine does the same. I suspect it is a machining error in whatever the RA rotates around. It might have a small impact on the polar alignment, but i suspect the error introduced by the operator looking up the polar scope and trying to polar align would be far greater than this causing mis-alignment with the NCP. You could always do the handset version of polar alignment once roughly polar aligned which i an now finding really good; a couple of cycles and the reported PA is under 5minutes out in elevation and azimuth; one or two more and you can get it to under one minute.

I suspect the imperfect machining (or whatever causes this odd rotating artefact) may also present some "periodic error" in the RA as the RA shaft sags a little as it passes this point, but it would be an infrequent error as only occurs once every revolution of the whole RA axis.

So i don't worry about it - yet.

Jd

[wxsatuser]

Yes it's quite noticeable on my HEQ5 but once the reticule is aligned there seems to be no problem.

I suppose I spent a good hour or more aligning the reticule on a neighbours tv aerial.

[jambouk]

Wxsatuaer - is yours now the same as mine? When the weight bar is pointing left, the cross hairs are directly over the target, when the weight bar is pointing right (after a 180 degree turn) the cross hairs are still directly over the same target, but when it is rotating between the two, the cross hairs drift off the target?

Jd