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Old 10-12-2017, 10:02 AM
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skogpingvin (Bill)
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Polar alignment confusion

Hi folks, Bill here

I'm in the middle of upgrading some stuff and I found I've painted myself into a corner over polar alignment.

My old system was an NEQ6 with a refractor with a DSLR and a guide scope. The guide camera is an ASI120MM. I use ASCOM with Stellarium and PHD2 for guiding. All worked pretty well. I used SharpCap 2.9 for polar alignment using the guide scope (I don't know how many people use this, but it's brilliant).

I've decided to ease my way into narrowband, so I got myself an ASI1600MM-pro, and there's an off axis guider on back order from Bintel. I plan to put the 120MM on the OAG and then go through the 1.25" manual filter wheel I have already. It's looking OK so far, although no first light yet. The only things I need now is Sequence Generator Pro, and some variable spacers for the back-focus of my flattener (also on back order).

Then I discovered the problem. Using the 560mm focal length refractor and the 1600MM I can't use SharpCap for polar alignment. You need a much shorter focal length for that - I guess it's to limit the size of the database for plate solving. I think (unless some clever person out there can help me) that I'm forced to unscrew the 120MM from the OAG and put it back on the old guide scope, polar align with that, then move it back to the OAG for the rest of the night. Not an optimal thing to be doing in the field, with dust and moisture.

A secondary problem is that I "fully extended" myself with the upgrade. I can't get a Polemaster, as that's currently out of my range. Can anyone think of a solution? SGP doesn't (yet) have a polar alignment aid, which is a bummer, because that would have been perfect.

Any thoughts?
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Old 10-12-2017, 11:46 AM
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billdan (Bill)
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Hi Bill

The only method I have used is drift aligning as my Sth Pole is blocked by trees.

As you have PHD2 there is a drift align menu you can use, it means pointing the scope to the North where the DEC 0 line crosses the Nth/Sth meridian line. This is to adjust the Azimuth bolts, and then point the scope the E or W near the horizon still at DEC = 0 to adjust the Elevation bolts.

This method is slower than your previous method, because you have to wait for the star in the OAG to drift and see if any adjustments are neccessary. Then you turn one of the Azimuth or Elevation bolts and drift again and wait and see if you have made an improvement.

If you haven't done this technique before it could take you 20 mins for the first time and then a lot faster when you are comfortable with drift aligning.

Cheers
Bill
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Old 10-12-2017, 12:53 PM
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lazjen (Chris)
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I also had to give up using SharpCap for the same reason.

PHD2 also another align tool - Polar Drift Align that you could try as well. There's also a new static polar align tool in there as well, but I have not had much luck with it as yet, since it wants me to pick a particular star and I haven't got any idea what is what there. It probably needs some form of plate solving to go with it to make it really useful.

Another option is to install Astrotortilla. It does plate solving, but also has a PA routine that does not require seeing the south pole. Can be useful for those locations where it's obscured.
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Old 10-12-2017, 03:45 PM
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skogpingvin (Bill)
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Quote:
Originally Posted by billdan View Post
Hi Bill

The only method I have used is drift aligning as my Sth Pole is blocked by trees.

As you have PHD2 there is a drift align menu you can use

Cheers
Bill
Hi Bill, Bill here. This could get confusing.

Hmm, that sounds good. I have done drift alignment with PHD2 before. It's slower but probably more accurate than Polemaster/SharpCap, especially as I'd be using the guide scope. I guess I have to get it roughly aligned first though. Any idea how roughly is practical for drift alignment?
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Old 10-12-2017, 03:51 PM
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skogpingvin (Bill)
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Quote:
Originally Posted by lazjen View Post
I also had to give up using SharpCap for the same reason.

PHD2 also another align tool - Polar Drift Align that you could try as well. There's also a new static polar align tool in there as well, but I have not had much luck with it as yet, since it wants me to pick a particular star and I haven't got any idea what is what there. It probably needs some form of plate solving to go with it to make it really useful.

Another option is to install Astrotortilla. It does plate solving, but also has a PA routine that does not require seeing the south pole. Can be useful for those locations where it's obscured.
OK, both of those sound promising - I already use Astrotortilla for synching Stellarium, and I know that SGP uses it as well - or at least the astrometry.net indices. As to the static polar align in PHD2, that I've never heard of. Is it in a new version or something?

Thanks for the suggestions!

Bill
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Old 10-12-2017, 04:02 PM
glend (Glen)
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There is no reason you should not be able to use Sharpcap PA with your refractor. I used it with my TS115 f7 APO, which is 636mm fl with the reducer. It worked perfectly.
Even if it did not work for some reason, your old guidescope can be used to align with Sharpcap, it does not have to be your main scope (as long as the guide scope is setup to be as straight as the main scope it should be fine). Your guide camera is sensitive enough to be used for alignment.
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Old 10-12-2017, 04:03 PM
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lazjen (Chris)
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The new static polar align in PHD2 is in the latest beta builds.
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Old 10-12-2017, 04:04 PM
glend (Glen)
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Originally Posted by lazjen View Post
The new static polar align in PHD2 is in the latest beta builds.
Which is an operational copy of how Sharpcap PA works.
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Old 10-12-2017, 04:16 PM
kens (Ken)
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Quote:
Originally Posted by lazjen View Post
I also had to give up using SharpCap for the same reason.

PHD2 also another align tool - Polar Drift Align that you could try as well. There's also a new static polar align tool in there as well, but I have not had much luck with it as yet, since it wants me to pick a particular star and I haven't got any idea what is what there. It probably needs some form of plate solving to go with it to make it really useful.

Another option is to install Astrotortilla. It does plate solving, but also has a PA routine that does not require seeing the south pole. Can be useful for those locations where it's obscured.
I'd recommend starting with Polar Drift Alignment to get within about 10arcmin. It's quick and easy. Once you can reliably point near the pole the Static PA star map helps you identify the stars you can use for a more accurate PA. Traditional drift alignment is the most accurate of all of them.
I've described the process I use at http://www.iceinspace.com.au/forum/s...d.php?t=163216
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Old 10-12-2017, 04:34 PM
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billdan (Bill)
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Quote:
Originally Posted by skogpingvin View Post
Hi Bill, Bill here. This could get confusing.

Hmm, that sounds good. I have done drift alignment with PHD2 before. It's slower but probably more accurate than Polemaster/SharpCap, especially as I'd be using the guide scope. I guess I have to get it roughly aligned first though. Any idea how roughly is practical for drift alignment?
You don't have to use the guide scope to drift align, if you paid for an OAG use that and ditch the guide scope.

To get it roughly aligned from scratch at a new site, you will need a compass and get the mount pointing as close to the Sth pole as possible. The compass points to Magnetic Sth so you will need to point East a further 11 degrees to get the Celestial Sth Pole.

I think the range of adjustment of the AZ bolts on the EQ6 is +/- 3 degrees so you will have to get the tripod pointing within that range.

If this site is going to be repeatable then put some markers on the ground for your tripod to align to. I used some old drill bits and hammered them into the ground with just 10mm showing (I also used fluoro paint so I could see them in the dark) and then butted the tripod legs up against them next time I used that site.

You can use an inclination meter for Elevation but that shouldn't have changed from the last time you used the mount.

Hope this helps
Bill
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Old 10-12-2017, 07:17 PM
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Quote:
Originally Posted by kens View Post
I'd recommend starting with Polar Drift Alignment to get within about 10arcmin.
10 arc min? That is the distance of the +6.9 BQ Oct to the pole. So center that star in the polar scope which is much easier.
And then refine until the required accuracy.
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Old 10-12-2017, 09:28 PM
kens (Ken)
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Originally Posted by skysurfer View Post
10 arc min? That is the distance of the +6.9 BQ Oct to the pole. So center that star in the polar scope which is much easier.
And then refine until the required accuracy.
That's perfectly fine but if you are a long way out on PA it can be hard to find. Once you are within 10' you can just centre the centre of rotation in the middle of the sensor and BQ Oct and the other possible reference stars are easily visible.
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Old 11-12-2017, 09:08 AM
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skogpingvin (Bill)
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Quote:
Originally Posted by glend View Post
There is no reason you should not be able to use Sharpcap PA with your refractor. I used it with my TS115 f7 APO, which is 636mm fl with the reducer. It worked perfectly.
Really? That'd be great! (Of course I can't go out into the back yard to try it yet - the OAG is still yet to arrive from Bintel, so it's still in bits on the study floor).

I do have a couple of different observing sites, the LMDSS in Victoria as well as my back yard, and I've been up to Wyperfeld a few times (the dark skies there blow the LMDSS away), although power is a problem.

My refractor is a 107mm flattened to a focal length of 560mm, so slightly wider than yours. In a new location, do you find it hard to get it roughly aligned close enough for SharpCap to take over?

(I guess there's only one way of finding out...)

Thanks for that!

Bill
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Old 11-12-2017, 09:20 PM
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skogpingvin (Bill)
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(I guess there's only one way of finding out...)
Grrr, sunny all afternoon, got home and had it all set up waiting for dusk and as soon as we started to see the first stars, Melbourne clouded over. Don't you love it?
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Old 15-02-2018, 02:56 PM
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skogpingvin (Bill)
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Just for completeness, I guess I should tie up this thread by saying yes! It does work. I can get a good polar alignment using nothing but the scope, the main imaging camera and SharpCap 2.9's polar alignment tool. It's cost me nothing. Of course, if you have a narrow field it's probably not going to work for you. My FOV is about 1.3 x 1.8.
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Old 15-02-2018, 03:23 PM
AstroApprentice (Jason)
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Hi Bill,
FYI, you mentioned you use Sharpcap 2.9. Although version 3.1 now requires purchasing the Pro license for 10 GBP, you can download 3.0.4076 for free.
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Old 15-02-2018, 03:35 PM
Imme (Jon)
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I agree with Bill, Sharpcap (V2.9) polar alignment tool is awesome to use.
I aligned my HEQ5 the other night down to 5 arc seconds within 10 minutes....awesome piece of kit.

.....although I did then misalign out to about 30 arc seconds to allow my guiding to operate better.....bounced back and forth across the arc across the pole otherwise!
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Old 15-02-2018, 03:36 PM
Imme (Jon)
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Originally Posted by AstroApprentice View Post
Hi Bill,
FYI, you mentioned you use Sharpcap 2.9. Although version 3.1 now requires purchasing the Pro license for 10 GBP, you can download 3.0.4076 for free.
You may still find 2.9 in the downloads section of their website....I grabbed it off there approx. 2 months ago
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Old 15-02-2018, 04:41 PM
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Merlin66 (Ken)
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SharpCap V3.1.5027 is still available for free download.
Some "advanced" features are now only available in the $$$ pro version, but everything works 100%
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