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  #1  
Old 22-02-2016, 02:17 PM
kens (Ken)
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Electronic Polar Alignment Scope

No, not the PoleMaster although it does apparently now work in the Southern Hemisphere.
But inspired by the idea I rummaged around in my spares box where I had two polar scopes. One for the Super Polaris and the other for the SW EQ6.
Both are pretty much identical with the exception of the screw thread for the eyepiece, slightly different focal lengths and therefore slightly different reticles. In fact the SP reticle is epoch 1980 as well I think.
And of course both are pretty much useless especially under light polluted skies.
But tinkering about I discovered that the thread for the screw on ring for the month dial is exactly the same as that on my DBK21AU04.
But to make it work I'd have to cut off the tube where the eyepiece screws in to expose those threads. So which scope to sacrifice? The SW scope drew the short straw. I'm keen to keep the SP in as close to original condition as possible and its polar scope is decidedly better quality than the SW.
I hacksawed off the tube then filed it down smooth. I had a couple of goes at it as at first it was still too long to focus.
I tested the focus first on the Dandenong TV towers and then on the moon. When the stars finally came out I refined the focus further. To do this I was using a camera tripod so I had to point close to the pole to reduce the star movement.
Next step was to take a pic and plate solve. This told me FOV (2x1.5 degrees) and pixel size (11 arc-seconds) from which I could calculate a 105mm focal length.
Checking against Stellarium I could see that the dimmest stars visible in the image were around mag 8. Then looking at the FOV around the pole in Stellarium I could see that the stars there are mag 7 to 8 so I should be able to get a usable image.
The theory is that I can take an image and plate solve. Then rotate the RA axis 180 degrees and do the same again. Taking the midpoint should account for any collimation error and tell me where the mount is pointing. Then I can adjust accordingly and iterate as required.
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Old 23-02-2016, 09:08 AM
Stefan Buda
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Yes, but wouldn't it be easier to use the afocal method and not having to cut the polar scope? You only need a cheap Jaycar lens and a 3Dprinted adaptor sleeve.

http://www.thingiverse.com/thing:1144293
http://www.thingiverse.com/thing:1102513
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  #3  
Old 23-02-2016, 12:41 PM
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multiweb (Marc)
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Sounds good. Regarding LP I actually find it easier to polar align when there are less stars visible in the polar scope. I have the Losmandy one on my G11. The reticule is probably outdated but it still gets me very close and I know how and where to offset the two stars I'm looking for.
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Old 23-02-2016, 02:42 PM
el_draco (Rom)
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Great idea, especially if you have a buggered up neck and live way South. Be interested in whether anyone has adapted a G11 polar scope like this.

Rom
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  #5  
Old 23-02-2016, 06:08 PM
kens (Ken)
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Quote:
Originally Posted by Stefan Buda View Post
Yes, but wouldn't it be easier to use the afocal method and not having to cut the polar scope? You only need a cheap Jaycar lens and a 3Dprinted adaptor sleeve.

http://www.thingiverse.com/thing:1144293
http://www.thingiverse.com/thing:1102513
This way is free and collimation should be more reliable.
It's not like the polar scope is useful. It is unnecessarily accurate for visual with a lot of effort to use it, or it is not accurate enough for imaging.
I usually jump straight to drift alignment but the plate solve method can potentially get the PA down to 30". This experiment should tell me one way or the other.
Besides, I've got another one still in the spares box.
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  #6  
Old 23-02-2016, 07:52 PM
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RobF (Rob)
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Be interested to hear updates Ken. Was cogitating over something similar recently. Key thing is to make it worthwhile time-wise for the benefit in an initial set up (I'm thinking astrophotography).
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  #7  
Old 23-02-2016, 09:23 PM
Stefan Buda
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Recently I made an adaptor for a Losmandy polar scope and just a few minutes ago a published the design on Thingiverse:

http://www.thingiverse.com/thing:1363374
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Old 25-02-2016, 07:55 PM
el_draco (Rom)
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Quote:
Originally Posted by Stefan Buda View Post
Recently I made an adaptor for a Losmandy polar scope and just a few minutes ago a published the design on Thingiverse:

http://www.thingiverse.com/thing:1363374
So this adapter slips over the polar scope in situ?
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  #9  
Old 25-02-2016, 09:41 PM
Stefan Buda
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Yes it does and it relies on the elasticity of the plastic to get a grip.
The Thingiverse site lets you rotate the model and look inside it without having to download it. If you do that then you'll understand how it works.
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Old 26-02-2016, 01:10 AM
kens (Ken)
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So tonight I started to use the scope to polar align experimentally. Plate solving was good to get close to the pole. But then I hit a snag as I was looking at Stellarium with JNOW coordinates whilst astrometry was giving the position in J2000. Until I realised what was going on I was puzzled as to why I appeared to be at the pole visually in Stellarium while astrometry wsa telling me I wasn't. The difference is about 4 arc-minute which is signficant. It seems it would be easiest to just use the nearest asterism and visually centre on the pole in relation to that. BQ Octanis is almost exactly 10 arc-minutes from the pole and was easily visible in the scope. I was about to try that when the clouds rolled in.
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  #11  
Old 01-03-2016, 03:48 PM
kens (Ken)
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Finally got to do a serious test last night even though it was a bit rough and ready. I just plonked the tripod down and took a pic and plate solved it. I needed about 8 seconds exposure to get a solvable image. The astrometry program gives results in J2000 so I plugged the results in Stellarium and it gave me back the Azimuth and Altitude. So all I had to do was adjust Azimuth to be 180 and Altitude to be my Latitude. I ended up getting close to the SCP. However, I knew that was illusory as the next test was to see how much collimation error there was. To do this I took an image with the mount rotated 6 hours west and 6 hours east, Plate-solving each one. Rather than calculate the results outside with the mozzies I then retired indoors for some analysis.
Using the plate-solved images with significant objects highlighted I could plot the centre of each image (all 3) onto a single picture. Then joining the dots gives a circle whose centre is where the mount is really pointing. This coincides with the centre of the line joining the East and West images but is useful for future reference.
Next step is to get an image with the mount actually pointing at the SCP as a reference for alignment. Basically the idea is to be able to say if BQ Oct and HIP42708 are horizontal on the image then the image should be centred at...
Alternatively, any ideas for collimation are most welcome
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  #12  
Old 01-03-2016, 04:08 PM
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For reference.

https://www.youtube.com/watch?v=5L6IvfievRE
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Old 10-03-2016, 03:55 PM
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It seems that PoleMaster software works only with PoleMaster hardware.. and that hardware is just USB camera with some specific ID that enables PoleMaster software.

Is there equivalent application, that will worlk with any camera?
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Old 10-03-2016, 10:04 PM
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Quote:
Originally Posted by bojan View Post
It seems that PoleMaster software works only with PoleMaster hardware.. and that hardware is just USB camera with some specific ID that enables PoleMaster software.

Is there equivalent application, that will worlk with any camera?
Writing an ASCOM-based application to work with any camera would be a simple enough task, but the QHY PoleMaster is covered by Chinese patent. Aside from that, PoleMaster and the supplied software costs around the same as a low-end guiding camera.

The software needs a couple of minor tweaks for usage at the SCP, but why hack something together and disregard patent when you could be supporting a company which is delivering affordable imaging products to the Australian market?
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Old 10-03-2016, 11:41 PM
kens (Ken)
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Quote:
Originally Posted by bojan View Post
It seems that PoleMaster software works only with PoleMaster hardware.. and that hardware is just USB camera with some specific ID that enables PoleMaster software.

Is there equivalent application, that will worlk with any camera?
That's more or less what I'm working/playing on. Thus far I have put together a spreadsheet to calculate Alt and Az from a plate solved image taken along the polar axis. Much easier than using Stellarium to do the calcs. I'm taking two measurements 180deg apart in RA so as to calculate the midpoint to account for collimation error.
From alt and az it's trivial to work out the adjustments needed for PA.
In due course it should not be hard to write up a program to do the calcs and read the FITS file header for the correct time when the image was taken, for more accurate calculation of alt and az.
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Old 11-03-2016, 07:44 AM
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Quote:
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....but why hack something together and disregard patent when you could be supporting a company which is delivering affordable imaging products to the Australian market?
Brett, I don't think US$268 is affordable at all. Not for me, and I am sure I am not alone here.
And, we are not professionals... IMO, DIY and free sharing of the knowledge is always preffered approach for us amateurs, and I wish it to be adopted much wider in our community, and actually encouraged - it is beneficial for our AU economy in the long run.

Of course - if someone is able and willing to pay for particular off-the shelf commercial product for whatever reason, I have no problem with that.. I bought my EQ6 because I didn't have time/tools to build my own.

Last edited by bojan; 11-03-2016 at 12:38 PM.
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Old 11-03-2016, 09:24 AM
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I think what PoleMaster does is much simpler, no plate solving is involved - actually, IMO the app first follows the alignment procedure for polar finder (by using the changing position of one star near the pole and rotating the mount for 180 it is easy to determine where the mount axis is pointing at - this is exactly between the two positions of the star on the screen, before and after rotation).
The next step is leaving the star to drift for a while without tracking.. Which will determine the position of the pole on the screen.
All that is left then for app to do is to tell you where to place the image of the star on the screen to align the mount.
The math involved in this process should be very simple... Definitely worth the effort.

Of course, the sensitivity of the camera and the size of the polar finder lens will be the issue.
The modified webcams (with long exposure times) will be a preferred option.

Last edited by bojan; 11-03-2016 at 09:47 AM.
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Old 11-03-2016, 09:37 AM
kens (Ken)
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Speaking of patents: http://www.google.com/patents/CN204269938U
As I read it the principal claim is the mechanical configuration integrated with the electronic alt-az sensors. But I am no patent attorney.
The software could be based on this work by Rick Kellogg. http://www.syracuse-astro.org/pdf/20...ment_Scope.pdf
I need to study Kellogg's paper as I might be able to do something similar using BQ Oct and HIP 42708
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Old 11-03-2016, 01:59 PM
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I am looking again at the method I described earlier (believing it was what PoleMaster is doing), and the patent..
In patent they are mentioning all sorts of things, and this reading is additionally confused by bad translation into English.. I am sure even patent attorney would have been puzzled (or maybe not..).

Anyway, I am not sure the existence of patent is relevant for amateur activity at all – firstly, because the aligning method of two rotating axles is nothing new and basically a common sense issue, and in public domain for a long time. Secondly, no one here is trying to copy, manufacture and/or sell the product as competitor.

Finding the point where the polar axis is pointed at is accomplished with rotation by 180 all right.. mechanical setting circles can be used for better accuracy, or perhaps the bubble level on the DEC axis .

To find the celestial pole, however, it is better to use couple of stars, located around the pole (it is easy to recognize the asterism around sigma Octantis, and all those stars should be used, perhaps others at the other side of the pole as well).
They should be marked on the screen (and their positions stored) at their starting positions and then the tracking should be stopped. After some time the image on the screen will rotate… and the same stars should be marked again as end positions.
Software needs to place the joining lines between stars start and stop positions, calculate the mid points and then place the lines through those points perpendicular to joining lines. The intersection between all perpendicular lines is true celestial pole.

The vector defined by the point where polar axis is aimed (start) and the abovementioned intersection point (end) determines the amount and direction (negative) to move the star image (by adjusting the mount elevation and azimuth screws) from current marked position to the new one (indicated by software).
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Old 12-03-2016, 01:29 AM
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Quote:
Originally Posted by bojan View Post
And, we are not professionals... IMO, DIY and free sharing of the knowledge is always preffered approach for us amateurs, and I wish it to be adopted much wider in our community, and actually encouraged - it is beneficial for our AU economy in the long run.

Of course - if someone is able and willing to pay for particular off-the shelf commercial product for whatever reason, I have no problem with that.. I bought my EQ6 because I didn't have time/tools to build my own.
Bojan,

You're right, we're not professionals and I apologize if I came across as though I'm against the DIY aspect. I am all for the concept of home-brew and respect that it is and always has been an integral part of the amateur movement.
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