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Polarscope reticule misaligned on heq5


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Hey everyone, i know this is a question that has probably been asked a million times but i need some help with it.

When my scope is in the home position with DEC axis at 0° and perpendicular to the RA axis, the clockface reticule in the polarscope is twisted clockwise 2 hours too far i.e. showing 12oclock where 2oclock would be on an upright clockface and 6 oclock where 8oclock would normally be. 

My question is where should i position polaris using its hour angle for my long/lat/time to get proper PA?

This is causing my grief as take this example- say i use my current clockface where 12 oclock is where 2oclock should be, if polaris hour angle was 8oclock say, I'd positon it at 8oclock on the clock face. If i rotated my RA axis so that 12oclock was at the 'top' and 6oclock at the 'bottom', that same alignment of 8oclock on the twisted reticule would mean polaris would be at 10oclock on the upright clockface - a difference of 2 hours.

Should i position polaris using an upright clockface (i.e. rotating my RA axis slightly so 12 is at the top) or position it on the wonky clockface where 12 is at 2? I have already calibrated my polarscope so that objects stay centre if you rotate the RA axis.

Hope someone can shed some light on this, thanks.

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The instructions on our EQ6 say to rotate the RA axis until 12 o'clock is at the top. To me this seems a bit crazy, given the cost of the mount & the risk in not getting the reticule rotation aligned perfectly.

Once the RA is rotated, I use the alt/az bolts to check the horizontal/vertical are aligned on the axis' as best I can, before positioning polaris at the required time on the clock face.

Cheers
Ivor

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1 hour ago, Aramcheck said:

The instructions on our EQ6 say to rotate the RA axis until 12 o'clock is at the top. To me this seems a bit crazy, given the cost of the mount & the risk in not getting the reticule rotation aligned perfectly.

Once the RA is rotated, I use the alt/az bolts to check the horizontal/vertical are aligned on the axis' as best I can, before positioning polaris at the required time on the clock face.

Cheers
Ivor

Thanks Ivor - will try that way next time I'm out. I agree it seems odd as to why they wouldn't just align the clockface reticule upright in the first place. It's an extra thing to fumble about in the dark with.

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Having just been outside to align a finderscope, I noticed that I've made a mark on the mount with a Sharpie pen to show approx. how far round I need to rotate the RA in order to orientate the polarscope reticule correctly. (i.e. I rotate RA until the "0" is on the Sharpie mark)

Not terribly accurate, but might be something to consider...

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1 hour ago, eikie said:

Pardon my ignorance, but if polar aligning is all about pointing the RA axis of the mount towards the NCP, what effect is there when I rotate the mount around that axis?

The stars appear to rotate around the Earth's axis of rotation.  If the RA axis is aligned with that of the Earth then they will also appear to rotate about the RA axis in the same way, so if you now rotate the mount about the RA axis at the same speed as the stars appear to rotate then as far as the view through the telescope is concerned, the stars appear to stay still.

James

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5 hours ago, JamesF said:

The stars appear to rotate around the Earth's axis of rotation.  If the RA axis is aligned with that of the Earth then they will also appear to rotate about the RA axis in the same way, so if you now rotate the mount about the RA axis at the same speed as the stars appear to rotate then as far as the view through the telescope is concerned, the stars appear to stay still.

James

I do get that, however, if you are polar aligning, you align the RA axis of the mount. Does rotating the mount in it's RA axis make a difference for polar alignment?

 

If I look at my polar scope while the mount/telescope is in the home position, the reticle shows the numbers (0/3/6/9) not in the correct position (i.e. the 6 is almost on top).

The only way to get the 0 on top, is to rotate the mount in the RA axis, in my case untill the counterweigth bar is pointing up.

Is that required though?

 

Lets say my handcontroller or Polaris finder app tell me to put Polaris at exactly the bottom of the reticle, does it matter if I leave the mount in the home position, showing the 0 (almost) at the bottom of if I turn the mount so the 0 is at the top?

Assuming the polar scope is properly calibrated, in both cases, I put Polaris at the same physical spot on the circle, only the corresponding numbers change.

 

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No I don’t suppose it does matter as long as the view through your polar scope and the position of Polaris matches that of your app.

To callobrate your polar scope place Polaris at the centre of your polar scope. Then using the altitude bolt only lower the mount until Polaris is on the outer ring at the top, then rotate in RA to put 12 o clock at that point. Your scope is now perfectly calibrated and you can go onto polar alignment. This method does depend on the mount being level

Edited by Jiggy 67
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I'm new to this and I may be talking rubbish but I have a recent HEQ5 which I'm just getting used to. The one I have has the new reticule which does not show Ursa Major or Ursa Minor.

I'm not sure if your definition of home position is the same as mine. When using the polar scope I put the RA such that the counterweight bar is pointing down the North leg of the tripod. The dec is rotated such that hole in the shaft allows you to see through the polar scope.  Then when I look through the polarscope  the 0 on the reticule is roughly in the 2 o'clock position. In order to set up the PA you have to rotate the RA such that the 0 is at the top. The mount is no longer in what I call the home position.

Then when you put all the time and position data in the handset it will give you HH:MM for the correct position of polaris with the mount in that position. SO you adjust the mount to put polaris in the correct place on the reticule. It seems to work. I'm not sure what's going on but I think what's happening is that it's simply using the circle on the reticule with the zero at the top as a convenient kind of fixed reference not related to where the scope is actually pointing.  You know polaris should be somewhere on that circle. The easiest way to say where it is is to always have the reticule in the same position with 0 at the top.

 

 

 

 

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So long as the position of Polaris on the ring in your PA scope matches that of the app it really doesn’t matter. 
 

I think PA reticules would be better off just being a plain circle for the northern hemisphere - would save so much confusion. 

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I think it's just a convenient to get the "0" at the top, so that it's easier to position Polaris at the correct time. Here's a picture of my polarscope taken through a DLSR right-angled viewfinder which I temporarily attach when setting the position. It's got a 2.5x magnification switch for fine tuning.
Obviously once Polaris is in the right place, you rotate the RA back to it's home position...
 

polar_1.jpg

polar_2.jpg

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2 hours ago, dannybgoode said:

So long as the position of Polaris on the ring in your PA scope matches that of the app it really doesn’t matter. 
 

I think PA reticules would be better off just being a plain circle for the northern hemisphere - would save so much confusion. 

That is what I was thinking, but as a beginner I wasn't sure.

 

Rotating your mount around the RA axis just to get the numbers right can't have any effect on polar alignment on that same axis (assuming the callibration is done correctly), at least that seems logical, but I might be very wrong.

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I asked a similar question here: 

 

As others have said, it's convenient and reassuring to have zero at the top but ultimately it makes no difference where the numbers are provided you assume that the top of what you can see is zero and align accordingly.

Mark

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On 30/11/2019 at 08:58, Aramcheck said:

Once the RA is rotated, I use the alt/az bolts to check the horizontal/vertical are aligned on the axis' as best I can, before positioning polaris at the required time on the clock face.

 

great tip! I like that.  Another suggestion it aligning with something vertical in the daytime (i.e. side of your house) and making a note on the RA clock where it is to rotate to in the dark.

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