Polar alignment without pole star

[markclaire50]

2 hours ago, AndyKeogh said:

Hi Mark,

I faced your problem last night when setting up my equipment at a very dark campsite in Dumfries an Galloway.  I was just setting alignment via the polar scope when the clouds rushed in but there were a few stars visible to the south so I had to complete the task with drift alignment using PHD2. 

I only went for one iteration of each axis but that was good enough or 2 minute subs with less than half a pixel movement in either axis between subs.

My advice is place your scope where you will get the images you want, learn drift alignment, as Olly Penrice would say, it is the gold standard.  

If you set up your scope at the bottom of the garden you should be able to get your altitude setting pretty well set up as long as you make sure it is levelled first.  Move it up to your patio or location of choice, relevel, use a compass to align with north and then play with drift alignment. A nice feature of PHD 2 is that you can make some notes as you align and it will remember these for your next session. For AZ ,I record which alignment bolt to tighten depending on whether the slope is positive or negative.  For altitude adjustment I record which direction the star should move according to the sign of the drift.

HTH

Andy

Thanks Andy

I hope I have sufficient intelligence for all this! ? 

Not to mention the strength to carry the whole setup down the garden. 

I was looking at the end of my garden at the the paved area and thinking how long it would take before I fell backwards into the flowerbed! There is a 4 inch high wooden separator to stop soil going onto paved area. Perfect to forget in the dark! ?

[AndyKeogh]

7 hours ago, markclaire50 said:

 

Not to mention the strength to carry the whole setup down the garden. 

 

You could just take the mount down as all you want to do is set the altitude so that you have a reasonable start point for drift alignment. 

 

7 hours ago, markclaire50 said:

I was looking at the end of my garden at the paved area and thinking how long it would take before I fell backwards into the flowerbed! There is a 4 inch high wooden separator to stop soil going onto paved area. Perfect to forget in the dark! ?

Have a look on the net for illuminated tent pegs.  They work great on campsites to stop people walking into the scopes and they do not ruin your night vision.  

[markclaire50]

Went out today to see where polaris was according to my reliable app for live sky finding. I reckon I might just be able to see it above the roof top at one point on my patio but not the other about four foot away. But, I reckon that if I know it is just out of sight I can get a pretty good fix on it. Enough for AP? That remains to be seen. But maybe I will be OK and won't need to buy a new laptop just to do drift alignment. 

Mark 

[The Admiral]

The major mount manufacturers do have polar alignment routines for when Polaris isn't visible, and it might be worth sounding out users of this feature, and whether it is sufficiently close for AP.

I noticed also when reading the limited information currently available for the new iOptron CEM40, that:

"This mount also has an integrated electronic polar finder scope known as the iPolar. This tool ensures the accurate alignment of a telescope, even when the pole star is obscured."

Now, whether this tool is actually better than the other routines I wouldn't like to say (and it'd be too early to tell), but it does use it's own built-in polar scope, much like Polemaster I guess, but at least that's not one extra accessory you should need to buy. Does Polemaster only work when Polaris is visible? I've no experience of that, but someone will know.

Ian

[AlexK]

2 hours ago, markclaire50 said:

Went out today to see where polaris was according to my reliable app for live sky finding. I reckon I might just be able to see it above the roof top at one point on my patio but not the other about four foot away. But, I reckon that if I know it is just out of sight I can get a pretty good fix on it. Enough for AP? That remains to be seen. But maybe I will be OK and won't need to buy a new laptop just to do drift alignment. 

Mark 

The Star Drifting polar alignment method is in the toolbox of astronomers from ancient ages. If you don't have a laptop for that, just do it manually (see this guide , for example). Tedious, yes, but with the artificial TNP method I have described earlier it's needed only once, the Polar scope can be fooled well enough for your typical backyard AP subs after that.

Edited March 10, 2019 by AlexK
Narrowed terms.

[AlexK]

57 minutes ago, The Admiral said:

....

I noticed also when reading the limited information currently available for the new iOptron CEM40, that:

"This mount also has an integrated electronic polar finder scope known as the iPolar. This tool ensures the accurate alignment of a telescope, even when the pole star is obscured."

Now, whether this tool is actually better than the other routines I wouldn't like to say (and it'd be too early to tell), but it does use it's own built-in polar scope, much like Polemaster I guess, but at least that's not one extra accessory you should need to buy. Does Polemaster only work when Polaris is visible? I've no experience of that, but someone will know.

Ian

 

That's nonsense. iPolar is just a cheap camera on the end of the small telescope in the polar axis. So it cannot polar align without the clear view of the pole.

Actually, there is a simple computational way for that indeed, but in order to implement it, the iOptron CEM40 should be priced not just pathetic $2000, but $4000, as that will require two additional motors and gears installed to drive the polar axis for the "hassle-free" alignment without direct view to the Polaris...

Any even cheapest GoTo system, even Alt-Az, can adjust its motion model to compensate for bad (or none) polar alignment, but in most cases, that's insufficient for the AP due to the field rotation and overall tracking accuracy provided.

Edited March 10, 2019 by AlexK
Improved English wording

[AngryDonkey]

13 hours ago, AlexK said:

That's nonsense. iPolar is just a cheap camera on the end of the small telescope in the polar axis. So it cannot polar align without the clear view of the pole.

How do you know? It clearly says on the website that it works even if the polar star is obscured?

14 hours ago, The Admiral said:

Does Polemaster only work when Polaris is visible?

Yes, although I think it also works on the southern hemisphere as long as the southern pole region is visible.

[ZiHao]

After months of experimenting and practicing, I finally managed to achieve pretty decent polar alignment for my eq3 mount by doing drift alignment by Robert Vice plus drift alignment tool on PHD2. Make sure you choose the correct stars on the required portion on the sky, and use a good compass to roughly aim your tripod leg to North or you could use this method https://www.youtube.com/watch?v=rPdQ9pU9GJA , it really helps a a lot, trust me. Get ready to sacrifice a lot of imaging sessions just to master all the techniques to polar align  . At first I feel that living on the equator was very troublesome, but it provides a mixture of deep sky objects from both southern and northern hemisphere, which is the reason of why I love here now haha..

 

[AlexK]

7 hours ago, AngryDonkey said:

How do you know? It clearly says on the website that it works even if the polar star is obscured?

Yes, although I think it also works on the southern hemisphere as long as the southern pole region is visible.

 

Just looking at the image of the new mount provided. The iPolar is nothing more than the factory-integrated Polemaster. There is no pole finding eyepiece but USB ports on that end, and there are no other possible openings for a camera not looking at the pole. Website? The Polaris star is a very small object, so yes, it can be obscured, but the polar region must be visible in a good vicinity anyway. The FOV of the Polemaster camera is 10 deg, so the Polaris could be no more than 5 degrees below the edge of the roof (palm width, which is nothing), otherwise, there are no stars visible for the camera to plate-solve. Yes, it is possible to make a wider FOV camera for that, but that will degrade the alignment accuracy which is already just 5 arcmin (the stated 30 arcsec max is just the camera's pixel pitch).

Edited March 11, 2019 by AlexK
typos

[AngryDonkey]

12 hours ago, AlexK said:

Just looking at the image of the new mount provided. The iPolar is nothing more than the factory-integrated Polemaster. There is no pole finding eyepiece but USB ports on that end, and there are no other possible openings for a camera not looking at the pole. Website? The Polaris star is a very small object, so yes, it can be obscured, but the polar region must be visible in a good vicinity anyway. The FOV of the Polemaster camera is 10 deg, so the Polaris could be no more than 5 degrees below the edge of the roof (palm width, which is nothing), otherwise, there are no stars visible for the camera to plate-solve. Yes, it is possible to make a wider FOV camera for that, but that will degrade the alignment accuracy which is already just 5 arcmin (the stated 30 arcsec max is just the camera's pixel pitch).

Yes you are probably right, shame that would have been groundbreaking ?. 

[The Admiral]

2 hours ago, AngryDonkey said:

Yes you are probably right, shame that would have been groundbreaking ?. 

Best to keep an open mind until we have more information and user reviews I think. But it is true that Polemaster is also licensed to iOptron to market under their own brand.

Ian

Edited March 12, 2019 by The Admiral

[noah4x4]

On 04/03/2019 at 20:09, Filroden said:

+1 this

I don't know about Skywatcher mounts, but the Celestron mounts can polar align using any three stars. It does not need a view of Polaris. It does some wizardry and works out how other stars would move and you adjust your alt/az bolts to centre your chosen star (e.g. something close to meridian).

I echo this. I can't see Polaris due to obstructions but Celestron mounts have a feature called All Star Polar Align (ASPA). Works brilliantly with just HC or Starsense aided. Has also been added to Celestron's new CPWI software now in beta test.

[AlexK]

That ASPA is a much more viable idea, indeed: https://www.celestron.com/pages/all-star-polar-alignment#

Thank you for sharing!

Though, not helpful for the OP.

Edited March 12, 2019 by AlexK

[noah4x4]

6 hours ago, AlexK said:

That ASPA is a much more viable idea, indeed: https://www.celestron.com/pages/all-star-polar-alignment#

Thank you for sharing!

Though, not helpful for the OP.

Why not helpful to the OP that said he is planning to buy a mount? If his original choice can't meet his needs due to being unable to see Polaris his best option is to choose another mount that does offer a solution. 

[AlexK]

Just now, noah4x4 said:

Why not helpful to the OP that said he is planning to buy a mount? If his original choice can't meet his needs due to being unable to see Polaris his best option is to choose another mount that does offer a solution. 

Ahh! I've missed that turn. Then, sure thing, this is prob. the best solution.

[The Admiral]

I read a new post on the CN forum:

"Contacted iOptron about the iPolar and it will need a computer to work, so pretty well built in polemaster. It will be available for retrofit on other iOptron mounts though. "

That's disappointing, I was rather expecting that as it's using the iOptron branding that it would have been integrated into the handset, rather than requiring subsidiary computing power. If Celestron can do that with the Starsense, then in theory it ought to be possible. I guess it comes down to intellectual property rights.

Ian

Edited March 14, 2019 by The Admiral

[AlexK]

Wait a sec, but the Polemaster (QHY and Celestron) has the USB connection too. It should go into a real computer as well to make it work. The handset is just a microcontroller and has not enough computing power to plate solve images. And that's logical as otherwise, the price of the mount with it should be bumped for the price of a decent smartphone.

[The Admiral]

42 minutes ago, AlexK said:

The handset is just a microcontroller and has not enough computing power to plate solve images.

Well Starsense with it's associated hc seems to be able to do it, no additional computing power necessary. It identifies stars in each image and builds a model of the night sky. Of course, the Starsense is there for alignment, but it can be used in Polar alignment when Polaris isn't visible. I've never tried that feature as I've only ever used it with an Alt-Az mount, so I can't vouch for its success, but possible others can.

And given the price of the Starsense, I think it would fulfill your smartphone comparison!

Ian

Edited March 14, 2019 by The Admiral

[AlexK]

Wow! I didn't know that. Will study the Starsense's tech. Thank you for the tip!

[Ricker]

Do you need to be worried about how level your tripod is for polar alignment. Seems to me the altitude adjustment tips the mount anyway...