Polar alignment - polarscope off axis

[Gomtuu]

After tearing my hair out trying to polar align, I've come to the conclusion that the polarscope in my EQ5 is not actually aligned to the mount's rotational axis, as it seems to be coning, even when it's as finely adjusted as possible.

Is there any way to correct this?

[E621Keith]

The current EQ5 uses a newer polarscope design than my EQ4, but there should be three sets screws that will allow you to adjust the reticle position. Adjust it until the centre of the cross hair don't move when you rotate the RA axis, this will centre the reticule to your scope's axis. It does not matter if the edges of the AFOV moves, as long as the centre of your reticule is stable then you will be fine.

[Gomtuu]

I understand how to adjust the reticle, but I find that although it will stay centred relative to the image in the FOV, the image wobbles/cones as the mount rotates, suggesting that the polarscope itself is off axis.

Are you saying that this doesn't matter?

[brantuk]

It sounds to me like the polarscope wants collimating. To do this take it out and use an "L" frame. I wouldn't adjust it whilst in the mount cos you can't be sure it's still collimated after adjusting. Once you've set it right - thread it back into the mount and it should be aligned to the rotational axis of the mount.

Can I ask - how are you polar aligning? Just want to be sure you aren't aligning the center of the polarscope on the pole star but rather the small circle on the circumference of the larger circle. Then when you turn the RA axis the pole star should follow the circumference of the large circle. I wanted to be sure you're not mistaking this for "coning". HTH

[E621Keith]

I understand how to adjust the reticle, but I find that although it will stay centred relative to the image in the FOV, the image wobbles/cones as the mount rotates, suggesting that the polarscope itself is off axis.

Are you saying that this doesn't matter?

The AFOV image wobble doesn't matter as long as the reticle doesn't move (note the reticule doesn't necessary have to be in the centre of the AFOV). Best thing to do is to find a distant object in day time and centre the reticle on it. When you rotate the RA axis, the centre of the reticle should stay on the object and not move, once that is achieved then you reticle is centered on the mount axis of rotation.

[cantharis]

Good luck with all that. Excellent advice guys.

[bigbox]

Hi, heres a video i think might just help you out a little

regards Ady

[Gomtuu]

Thanks Keith, that's what I was trying to find out

[Gomtuu]

Hi Brantuk, I'm doing it in daylight on a static object, as I can only get out with the scope occasionally. I don't heve a problem with the main part of aligning, it's just that I wanted to be sure that the polarscope being slight off-axis doesn't matter, provided that the reticule is centred in the image (even if the image wobbles slightly!).

cheers, Mark

[brantuk]

Glad Keith sorted you out Mark

[glowjet]

There may be a reason for this, from an engineering aspect, if your mount has been levelled and in manufacture the mounts Polar access hole has been machined square with the vertical axis, then when turned through 180° the FOV should not alter, however, if in machining the threaded part of the tube for the Polar scope is not concentric with the hole, then when you screw in the scope it will revolve slightly off centre, your cone effect I think, as your FOV will appear to wobble, or it maybe your Polar scope is not seating properly when screwed home. I do not think there is any cause for concern, as you can take out the slight off centre by adjusting your reticule accordingly till it spins on centre, your FOV may wobble but your scopes central axis will be square to your mount which is what you set out to achieve in the first place. If I am wrong on this I am sure someone will comment, hope you sort it out

John.

[Gomtuu]

Hi John,

I suspect it was machined slightly off, but I wasn't sure about how significant it was for really accurate polar alignment. I think you've described what I'm seeing perfectly!