Polemaster questions

[Adam1234]

Hi all, I've got a couple questions regarding the QHY Polemaster.

On the step where you do the rotation (after double clicking on polaris, aligning the circles to the surrounding stars, selecting a star other than polaris and rotating the mount at least 30 degrees a couple times then you have to make sure the star stays in the green circle as you rotate back to the home position), I have trouble with getting it to stay on the green circle, it's either just off the circle straight away before even getting back to the home position, or off the circle by time it's back in the home position. I've never been able to get it to stay exactly on the circle. 

Has anyone got any tips on this bit? I've got the cable pointing East, and I use the hand controller for rotating the mount rather than using the clutches, and I try to click as centre to the star as I can, though that is very difficult and can't seem to always get right in the middle. 

Not entirely sure the stars are in perfect focus, perhaps adjusting the focus would help?

Also I normally have the tracking turned off while doing the polar alignment, is this correct or should it be turned on?

Any help appreciated.

Adam

[spillage]

Hi Adam,

I would suggest trying to get a better rough polar alignment and then try it again. I think this is caused by poor initial alignment.

cheers,

[Adam1234]

Cheers! I'll try that! So maybe if I run through the whole process a couple time then?

[spillage]

Not sure what kit you have but using alignment using the polar scope should be enough, or running drift align then fine tune in polemaster. So far the only issue I have had with polemaster is my monitor cable is VGA over Ethernet and for some reason I have a massive magenta hue which cancels out all green so cannot see the circle or the final green box for adjustment. I will not go into my way of dealing with it as its a bit bizarre....

Edited April 4, 2020 by spillage

[Adam1234]

9 minutes ago, spillage said:

Not sure what kit you have but using alignment using the polar scope should be enough, or running drift align then fine tune in polemaster. So far the only issue I have had with polemaster is my monitor cable is VGA over Ethernet and for some reason I have a massive magenta hue which cancels out all green so cannot see the circle or the final green box for adjustment. I will not go into my way of dealing with it as its a bit bizarre....

I'm using the SW EQ6-R Pro mount, and imaging, so alignment with just the polar scope is not enough, hence why I'm using polemaster. 

Bit confused with your issue, do you not just plug the polemaster USB into your laptop? 

 

[spillage]

If you are having to set up every time just run a rough alignment with the polar scope first.

I run a pc at the mount but have my keyboard, mouse and monitor about 5m away in the shed. It is probably a wiring issue in the cat5 but I'm too lazy to sort it.🤣

[Anne S]

I've used a Polemaster for several years mostly on my travelling mount. I use a compass to set the mount slightly east of magnetic north in daylight. When I start the alignment with the Polemaster, I don't bother with the handset, just loosen the ra clutches and move a generous 30 degrees each time. I probably move more than I need! I always end up with the stars on the green circle. Have you tried rotating further each time. I would expect it to be more accurate over the longer distance.

[Adam1234]

46 minutes ago, Anne S said:

Have you tried rotating further each time. I would expect it to be more accurate over the longer distance.

Yeah I tend to rotate about 45 degrees or so each time. Any more than that and the star ends up going out of the fov after the 2 rotations 

[Anne S]

9 minutes ago, Adam1234 said:

Yeah I tend to rotate about 45 degrees or so each time. Any more than that and the star ends up going out of the fov after the 2 rotations 

I find I need to zoom out to see enough on my laptop. Pity laptop screens aren't square!

[MarkAR]

Could it be that your mount isn't level ?

[Cornelius Varley]

2 minutes ago, MarkAR said:

Could it be that your mount isn't level ?

Whether the mount is level or not doesn't affect an equatorial mount. The RA axis just needs to be aligned with the NCP.

 

[MarkAR]

In that case all I can think of is that the Polemaster is either sitting askew in the holder, the holder is askew or the Polemasters optics are askew.

Also wondering if doing a 360º sweep will show up anything. If the star ends up in the same place at 0º and 360º but off the line everywhere else then that should bean the Polemaster isn't sitting aligned to the axis.

 

Edited April 5, 2020 by MarkAR

[Adam1234]

On 05/04/2020 at 11:59, MarkAR said:

In that case all I can think of is that the Polemaster is either sitting askew in the holder, the holder is askew or the Polemasters optics are askew.

 

 

I had a look at how the Polemaster sits on the mount and it does look more snug to some parts of the mount than others, but after taking it off, I noticed this is because the part of the mount that is attaches to (where the polar scope cap normally goes) is not itself level (with respect to the mount) - it is slightly raised at the top end where it's more snug with the Polemaster adapter. 

Do you think this affects the alignment much?

All in all, the star is only just off of the green circle, not miles off, but I'm a bit of a perfectionist and want to get it as best as I can. I've still been able to get reasonably good 3-minute subs without guiding, but difficult to tell properly how good the PA is when I have comet shaped stars (waiting for field flattener to arrive which will hopefully sort that out).

I've got some pictures below to show how the polemaster sits.

From the bottom:

From the left side:

 

From the right side:

 

From the top:

[MarkAR]

Well it could very well be the surface on the mount in the last picture it looks suspect. Ideally that surface would be machined perfectly square with the axis.

I think if you try rotating the RA axis 360º next time you polar align and see at which point the star is furthest from the green circle. That might give you an idea of which side to either tilt the red holder or place a small shim under it. Then repeat the 360º ad nauseam till you're happy.

At a guess it looks like a gap where the thumbscrew is on the right.

[Adam1234]

9 hours ago, MarkAR said:

I think if you try rotating the RA axis 360º next time you polar align and see at which point the star is furthest from the green circle. That might give you an idea of which side to either tilt the red holder or place a small shim under it. Then repeat the 360º ad nauseam till you're happy.

That's a good idea thanks, I'll try that.

 

[Pompey Monkey]

It doesn't matter if the polemaster is perfectly aligned with the mount.

The entire point of the device is to locate the RA axis of your mount (by rotating stars on the green circle), and then aligning this axis to the NCP.

[Adam1234]

1 hour ago, Pompey Monkey said:

It doesn't matter if the polemaster is perfectly aligned with the mount.

The entire point of the device is to locate the RA axis of your mount (by rotating stars on the green circle), and then aligning this axis to the NCP.

If it is slightly tilted relative to the RA axis though, would it not calculate the centre of rotation incorrectly? Or perhaps by the amount it is titled in my case the error would be so small it's irrelevant?

As an example, if for some really strange reason one decided to attach the Polemaster on its side then obviously the centre of rotation would clearly be wrong (it probably wouldn't even be able to calculate it).

Just trying to determine why I'm finding it hard to get the star to stay on the green circle. It seems that after I have done the 2nd rotation, the star is just outside the circle, and is still off the circle by approximately the same amount by time I rotate back to the home position.

[Pompey Monkey]

1 minute ago, Adam1234 said:

If it is slightly tilted relative to the RA axis though, would it not calculate the centre of rotation incorrectly? No, this is exactly why the software asks you to rotate the mount twice - to determine the axis of rotation (RA).

As an example, if for some really strange reason one decided to attach the Polemaster on its side then obviously the centre of rotation would clearly be wrong (it probably wouldn't even be able to calculate it). Obviously the Polemaster needs to be pointing roughly in line with the RA axis, or it won't be able to find it.

Just trying to determine why I'm finding it hard to get the star to stay on the green circle. It seems that after I have done the 2nd rotation, the star is just outside the circle, and is still off the circle by approximately the same amount by time I rotate back to the home position. If the star starts on the circle, but then is off it after rotating back to the same position, then it suggests that the whole mount is moving while you rotate the RA axis. Are the altitude and azimuth adjustments moving while you rotate the RA axis? Is the ground/tripod solid?

 

[Adam1234]

56 minutes ago, Pompey Monkey said:

If the star starts on the circle, but then is off it after rotating back to the same position, then it suggests that the whole mount is moving while you rotate the RA axis. Are the altitude and azimuth adjustments moving while you rotate the RA axis? Is the ground/tripod solid?

It never even starts on the circle most of the time, and stays the distance from it as I rotate back to the home position.

It looks like there might be some clear skies tonight so I'll probably be getting the scope out and I'll take some screen shots. 

I think everything is pretty solid, I'll double check when I set everything up tonight

[CraigT82]

Have you tightened up the mount/tripod bolt before doing the rotations? Could be moving around if it's not tightened up after adjusting the alt/az mount adjusters

[Adam1234]

22 minutes ago, CraigT82 said:

Have you tightened up the mount/tripod bolt before doing the rotations? Could be moving around if it's not tightened up after adjusting the alt/az mount adjusters

As far as I'm aware. I'll double check everything when I set up tonight

[jimjam11]

6 hours ago, Adam1234 said:

If it is slightly tilted relative to the RA axis though, would it not calculate the centre of rotation incorrectly? Or perhaps by the amount it is titled in my case the error would be so small it's irrelevant?

As an example, if for some really strange reason one decided to attach the Polemaster on its side then obviously the centre of rotation would clearly be wrong (it probably wouldn't even be able to calculate it).

Just trying to determine why I'm finding it hard to get the star to stay on the green circle. It seems that after I have done the 2nd rotation, the star is just outside the circle, and is still off the circle by approximately the same amount by time I rotate back to the home position.

Have you run the PhD guiding assistant for a few minutes to actually measure your pa error after aligning with the polemaster? You might be trying to fix something which doesn't need fixing...

[jimjam11]

I have never used a polarscope with the polemaster. The pm has a wide field of view so you only need to be pointing vaguely north for it to work. In practice I try to get polaris somewhere near the middle of the screen before starting otherwise you can easily run out of az adjustment.

[Adam1234]

34 minutes ago, jimjam11 said:

Have you run the PhD guiding assistant for a few minutes to actually measure your pa error after aligning with the polemaster? You might be trying to fix something which doesn't need fixing...

No as I don't have PhD yet, or a guide camera. I've got a guide camera on order from FLO so when that arrives I will learn how to use PhD

[Adam1234]

Managed to get the star to stay on the green circle tonight, yay!!! No idea exactly what I done, but I'm happy. Capturing some subs of the Owl Nebula now, and stars are looking more or less fine with a 3-min exposures unguided 😀

Let's try not to overwrite the axis of rotation next time I align