How important is physical positioning in polar alignment?

[Ash2020]

Hi again. I'm still trying to get my head around polar alignment. It seems to me there are 4 variables:

1. The North leg of the tripod.
2. The bubble level
3. The Dec clutch position
4. The R.A. clutch position

What is the order of importance of these? I know they're all important but, for instance, what would give more accuracy, a perfect North on the leg but not quite level or absolutely level but a degree or two out on the leg position? Likewise, if the weight bar isn't precisely 90 degrees to the horizontal, is it a problem if it is counteracted on the other axis?

Sorry if I'm being pedantic, it's just about my understanding.

Cheers

Andrew

 

[Davey-T]

Don't worry where the weight bar is, you may have to rotate it to get a view through the polar scope.

Dead level is not necessary.

Don't worry about the clutches you're only aligning the RA axis not the clutches.

Basically ignoring everything get a view of Polaris through the polar scope, you may have to move the tripod legs to achieve this then refine with the bolts.

Dave

[Uplooker]

As Dave says, position of the leg is irrelevant, does not need to be level, the adjustment of the alt and Az bolts take care of everything.

Definitely make sure that you rotate the Dec axis so that it is at 90 deg to the mount so that the holes inside the mount align properly so that you actually get a view through the polar scope.

Also make sure that the counterweight bar is extended out sufficiently, again so that holes inside the mount are clear to allow a proper view through the polar scope.

[MartinB]

Ian is spot on.  The only thing that matters for polar alignment are the altitude and azimuth axes.  It has nothing to do with RA or dec other than you might need to move these to use the polar scope.  If you want a quick, rough and ready alignment for a visual session you might want to line up the RA with the north point of the azimuth and then line it up with polaris.  You can set the alt using your known latitude before hand but if you do this then you will want the mount to be level.   If performing a drift alignment it is nice to have the mount level so that the drift direction is straight up and down.

[brantuk]

Yup - the polar alignment is more important than any of your 4 variables.

[Ash2020]

2 hours ago, Davey-T said:

Don't worry where the weight bar is, you may have to rotate it to get a view through the polar scope.

Dead level is not necessary.

Don't worry about the clutches you're only aligning the RA axis not the clutches.

Basically ignoring everything get a view of Polaris through the polar scope, you may have to move the tripod legs to achieve this then refine with the bolts.

Dave

Thanks Dave. So it doesn't matter where the leg is, or how level the head is, as long as I can see Polaris?

[Ash2020]

1 hour ago, Uplooker said:

As Dave says, position of the leg is irrelevant, does not need to be level, the adjustment of the alt and Az bolts take care of everything.

Definitely make sure that you rotate the Dec axis so that it is at 90 deg to the mount so that the holes inside the mount align properly so that you actually get a view through the polar scope.

Also make sure that the counterweight bar is extended out sufficiently, again so that holes inside the mount are clear to allow a proper view through the polar scope.

Thanks for that. After I've got Polaris in the right place in the polarscope, how do I know where to put the weight bar?

[Ash2020]

1 minute ago, Ash2020 said:

Thanks for that. After I've got Polaris in the right place in the polarscope, how do I know where to put the weight bar?

 

1 hour ago, MartinB said:

Ian is spot on.  The only thing that matters for polar alignment are the altitude and azimuth axes.  It has nothing to do with RA or dec other than you might need to move these to use the polar scope.  If you want a quick, rough and ready alignment for a visual session you might want to line up the RA with the north point of the azimuth and then line it up with polaris.  You can set the alt using your known latitude before hand but if you do this then you will want the mount to be level.   If performing a drift alignment it is nice to have the mount level so that the drift direction is straight up and down.

That's what I was asking really. If the mount wasn't level, would it matter if it was compensated with the latitude? The effect through the polarscope would be the same.

[Davey-T]

4 minutes ago, Ash2020 said:

Thanks for that. After I've got Polaris in the right place in the polarscope, how do I know where to put the weight bar?

To carry out star aligning then you need the weight bar straight down north with the scope in the home position.

Polar aligning and star aligning are two separate things.

Dave

[Ash2020]

8 minutes ago, Ash2020 said:

Thanks Dave. So it doesn't matter where the leg is, or how level the head is, as long as I can see Polaris?

Dave, when you say refine with the bolts, is that refining the polar scope view, or the actual view through the telescope? If you align the polar scope view to Polaris there's nothing to say that when you mount the telescope, Polaris will be in the middle.

[Davey-T]

22 minutes ago, Ash2020 said:

Dave, when you say refine with the bolts, is that refining the polar scope view, or the actual view through the telescope? If you align the polar scope view to Polaris there's nothing to say that when you mount the telescope, Polaris will be in the middle.

Use the bolts to get Polaris in the right place in the Polar scope, if you then put the scope in an up / north home position you may be able to see Polaris in the main scope depending on its focal length.

If Polaris in in the middle of your scope it's NOT polar aligned properly.

If your polar scope is the sort with a continuous clock face circle you can check occasionally during a session to see if Polaris is tracking round in the circle and give it a little tweak to realign it.

Dave

[Ash2020]

1 minute ago, Davey-T said:

Use the bolts to get Polaris in the right place in the Polar scope, if you then put the scope in an up / north home position you may be able to see Polaris in the main scope depending on its focal length.

If Polaris in in the middle of your scope it's not polar aligned properly.

If your polar scope is the sort with a continuous clock face circle you can check occasionally during a session to see if Polaris is tracking round in the circle and give it a little tweak to realign it.

Dave

Thanks Dave. I'm starting to understand a bit better.

Andrew

 

[Davey-T]

When you consider what you're trying to do is aim a tube a few inches long accurately at a star some 430 light years away it's a miracle if you get anywhere near 

Dave

[Ash2020]

22 hours ago, Ash2020 said:

Thanks Dave. I'm starting to understand a bit better.

Andrew

 

One final question. Once I have the mount perfectly aligned with the NCP through the polar scope, I then put the telescope onto the mount. Assuming it doesn't quite line up with NCP because of mechanical inaccuracies in the dovetail, what do I do then? Do I start the GoTo alignment from there or do I centre the NCP in the telescope with the motors first? Am I right in thinking that I don't touch the screw adjusters?

Thanks

Andrew

 

[Davey-T]

You may or may not be able to see Polaris in the main scope doesn't matter,  start from the up north home position Dec 90 degrees weight bar straight down (unless your mount has different instructions) then do the star alignment routine starting from there, don't touch the bolts.

Normally you slew to a star centre it with the hand control then do the same on one or two more stars, the mount then knows where all the stars are in the sky from these reference points.

Dave

[Uplooker]

Hi Andrew,

I may have missed it in the previous post, but what mount are you using and secondly have you aligned the polar scope to the mount axis?

please note that proper alignment of the polar scope is critical to achieving good polar alignment and should be done to the best of your ability before even attempting polar alignment?

Have a read through you manual and or ask back here

[Uranium235]

Just getting the north leg pointing roughly north is good enough - it helps so you can get polaris in the polarscope without too much twiddling (more for speed than anything else), a compass will help you out there.

One side note though, if setting up on soft ground with a heavy mount it helps to make "feet" for your triplod legs. That way the setup wont sink into the soft soil over the course of the night (and affect your PA slightly over time). And of course, avoiding the all time #1 schoolboy error... kicking your tripod accidentally in the dark...lol

 

[N3ptune]

1 hour ago, Uranium235 said:

 avoiding the all time #1 schoolboy error... kicking your tripod accidentally in the dark...lol

 

I am not going to graduate, ever,  from school I fear.

[ronin]

Although the mount does not need to be level, there is the use of the latitude dial on the mount, this will assume that the mount is level. So if you put the mount down and set to say 50N by the dial to place you at the right latitude of your location then that 50 mark presumes that the mount is level. So locating Polaris is made easier if the mount is level.

Situation of it is not necessary to be level but it likely will help make life a little easier if it is.

[Ash2020]

On 31/01/2017 at 21:40, Davey-T said:

You may or may not be able to see Polaris in the main scope doesn't matter,  start from the up north home position Dec 90 degrees weight bar straight down (unless your mount has different instructions) then do the star alignment routine starting from there, don't touch the bolts.

Normally you slew to a star centre it with the hand control then do the same on one or two more stars, the mount then knows where all the stars are in the sky from these reference points.

Dave

Thank you Dave. One of the problems I've had so far is that the mount will slew to an alignment star but I can't always tell, if there are a few, whether I'm centring the right star. Also, if its not already in view, I don't know which way to manually move to find it. I guess practice makes perfect. I've just got a Telrad red dot finder which I think will make everything much easier.

 

[Ash2020]

On 01/02/2017 at 08:07, ronin said:

Although the mount does not need to be level, there is the use of the latitude dial on the mount, this will assume that the mount is level. So if you put the mount down and set to say 50N by the dial to place you at the right latitude of your location then that 50 mark presumes that the mount is level. So locating Polaris is made easier if the mount is level.

Situation of it is not necessary to be level but it likely will help make life a little easier if it is.

Thanks, that makes a lot of sense, although the pointer on the latitude dial is very hit 'n miss.

[Ash2020]

On 31/01/2017 at 22:11, Uplooker said:

Hi Andrew,

I may have missed it in the previous post, but what mount are you using and secondly have you aligned the polar scope to the mount axis?

please note that proper alignment of the polar scope is critical to achieving good polar alignment and should be done to the best of your ability before even attempting polar alignment?

Have a read through you manual and or ask back here

Hi there. I'm using an EQ5 with Synscan. Only just bought it so I didn't even know there was any adjustment on the polar scope. I will study the instruction manual.

By the way, I see you have an SPC900. I have one that I modified years ago for long exposures. It has a USB and an old parallel port cable. I can't for the life of me remember anything about it, but I certainly don't have a laptop with a parallel port any more. (Macbook pro). Is yours modded and if so, how do you control exposures? Thanks

Andrew

[Ash2020]

On 31/01/2017 at 22:50, Uranium235 said:

Just getting the north leg pointing roughly north is good enough - it helps so you can get polaris in the polarscope without too much twiddling (more for speed than anything else), a compass will help you out there.

One side note though, if setting up on soft ground with a heavy mount it helps to make "feet" for your triplod legs. That way the setup wont sink into the soft soil over the course of the night (and affect your PA slightly over time). And of course, avoiding the all time #1 schoolboy error... kicking your tripod accidentally in the dark...lol

 

Haha! yes! Or tripping over the wires like I did the other night!

Cheers

Andrew

[Uplooker]

Hi Andrew,

I do indeed have an SPC900 webcam but not modded for long exposures. I normally use SharpCap to control it although I have not use the camera in a while.

With regard to aligning the polar scope read from page 10 in the HEQ5/NEQ6 manual, particularly the bit entitled "Step 2:Aligning the Polar Scope Reticule"

[Ash2020]

14 minutes ago, Uplooker said:

Hi Andrew,

I do indeed have an SPC900 webcam but not modded for long exposures. I normally use SharpCap to control it although I have not use the camera in a while.

With regard to aligning the polar scope read from page 10 in the HEQ5/NEQ6 manual, particularly the bit entitled "Step 2:Aligning the Polar Scope Reticule"

Thanks Ian, that's very helpful.

Andrew