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Polar Align without Polaris?

astrophotography beginner
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16 replies to this topic

#1 kimiwaffles

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Posted 16 September 2019 - 05:22 PM

I live in the Northern Hemisphere but my view of Polaris is always blocked by my next door neighbors huge house, whether i’m in the front or back yard! How can I polar align without a view of Polaris? I need to be very accurate for long exposure photos. I have the Skywatcher HEQ-5 mount, and a guide scope.. if that matters. 

Thanks! 


Edited by kimiwaffles, 16 September 2019 - 05:25 PM.


#2 DSOs4Me

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Posted 16 September 2019 - 05:35 PM

I have the exact same problem. Here is what I did. Go on line and find your offset to north (mine was 11 degrees east). Use a decent compass, set the offset and your north. Take a yardstick (I used a long dowel) and lay it out with your mark to be straight inline. Set you tripod's north leg on the front mark and straddle your other tripod legs evenly on each side of the yardstick (or whatever straight edge you use. Mark all your tripod leg spots so you can set up exactly on the same spots each time. I use Starguide on my iPad to align the telescope to Polaris and then to get it dialed in I use PHD2 drift align. It will take some playing around but you can get nicely dialed in with some patients. Most mportant - Don't get discouraged!



#3 DSOs4Me

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Posted 16 September 2019 - 05:38 PM

One thing I forgot - Use an online GPS to get your Altitude setting as well for your location



#4 PlanetOrion

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Posted 16 September 2019 - 06:01 PM

Like mentioned, PHD2 Drift Alignment might be your best bet. There are many tutorials on YouTube. However, it is a bit tedious, and I wouldn't want to be doing it every time I set up. If you image from your house primarily, I would prioritize having a semi-permanent setup (ie. getting a Telegizmos 365 cover for your tripod/pier and mount) so you don't have to polar align often. smile.gif


Edited by PlanetOrion, 16 September 2019 - 06:04 PM.

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#5 Michael Harris

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Posted 16 September 2019 - 06:45 PM

I could not find the manual for this mount online but I am wondering if it has an “all star polar alignment” routine similar to the standard Celestron software. That allows you to polar align without seeing Polaris, after your two or three star alignment.



#6 Alen K

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Posted 16 September 2019 - 07:06 PM

I could not find the manual for this mount online but I am wondering if it has an “all star polar alignment” routine similar to the standard Celestron software. That allows you to polar align without seeing Polaris, after your two or three star alignment.

It's in there. See page 38. But does kimiwaffles (hah!) have the Pro model (which uses Synscan) or the non-pro, non-goto model? (I don't even think you can buy the latter anymore but if bought used...)

 

That is actually a very good suggestion. It may just be accurate enough because...

 

The required accuracy depends on the focal length, the length of exposure and whether or not guiding is done. And those all interact. Kimiwaffles specified in another thread (and in her signature) a Zenithstar 73, which has a focal length of 430mm. That's going to be in her favor. In the other thread it was also revealed she is guiding, another plus as far as PA accuracy; one doesn't need to be nearly as accurate as unguided. When guided, imperfect PA causes field rotation around whatever star is selected for guiding.

 

The only variable left is (sub) exposure time. For a standard DSLR (the other thread stated a Canon - I hope it's a fairly recent model) I don't personally recommend exceeding five minutes even in really dark skies. In light polluted skies you will likely not be able to expose that long in any case. IMO exposures of one to two minutes can work in any but the most light-polluted skies, even if they are non-optimal in really dark skies. I think the HEQ-5's polar alignment accuracy using the goto might just suffice for that. The SynScan manual says "Generally, users can get up to 1 arc-minute polar alignment accuracy after repeating this polar alignment process 2 or 3 times."


Edited by Alen K, 16 September 2019 - 09:52 PM.

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#7 Alex McConahay

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Posted 16 September 2019 - 10:44 PM

You can get a decent polar alignment with just a compass and knowledge of where you are.

 

First, set up your mount so that it's altitude is set to your latitude.

 

Then, make sure the top of the mount is level. (Yes, it is not absolutely necessary that your mount be level, but if it is not, then the latitude setting will be off, and every adjustment in one axis will adversely affect the setting in the other. ----- And there is no reason to start with the mount anything but level.)

 

Now, using a compass, set your azimuth so that you are pointing to TRUE North (not magnetic as on a compass----if you need to know how to correct a magnetic compass reading to true, just ask).

 

Now, do a simple drift alignment from PHD2.

 

If this is not a permanent installation, before setting up, be ready to mark the precise position of your tripod legs. If you are on grass, put down three pavers to hold your tripod, and mark those pavers. Next night set up in exactly the same place, and do a drift alignment.

 

Another trick.....after you have aligned as well as you can with the compass, and aded the altitude, put the scope in  "Home Position" (usually  at 90 d dec and counterweight down). Start the system and do a "goto" to a known bright star 40-60 degrees above the horizon in the east, near the celestial equator. When the scope goes there, center the star USING THE ALTITUDE AND AZIMUTH ADJUSTERS before doing your Drift Alignment i PHD2. This may save you some adjustment time. (It may not be possible with some mounts.)

 

Alex   



#8 jiawen

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Posted 17 September 2019 - 10:20 AM

Can you do star trail images? Because if you can, you can use the star trails and some geometry to work out where the celestial pole is. Find a few good, clear star arcs. Find the mid-point of each star arc, then draw a line exactly tangential to that point (or parallel to that line). Now, draw a line at a right angle to the tangential/parallel line, through the mid-point. The place where several of those right angle lines cross should be the celestial pole. A perhaps-clearer diagram:

 

polefinding 1a 448x400

 

'Course, even if that works, you then have to use the same position for your rig each time. But maybe worth trying.



#9 Phil Sherman

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Posted 17 September 2019 - 10:54 AM

Do a search on cloudy nights for "D.A.R.V" by Robert Vice. I use a modified version that I described in entry 38 of the following topic. I also use a slew rate of 1x sidereal. You can use this technique to validate your polar alignment. The 4-5 minutes it takes is time well spent.

 

 https://www.cloudyni...t/#entry9465080

 

I don't locate a star in the fov because there's always a few stars in it.


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#10 ajaymandke

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Posted 17 September 2019 - 11:02 AM

There are couple polar alignment methods (in addition to drift alignment in PHD2) when you dont have view of polaris. 

 

1) DARV - https://www.cloudyni...bert-vice-r2760  (supported in APT and N.I.N.A.)

2) Polar alignment using astrometry/plate solving - (astrotortilla or N.I.N.A.)  https://nighttime-im...n/tabs/imaging/

 

I have been using APT/Astro tortilla for Polar alignment but recently tried N.I.N.A and both are very fast using astrometry.

 

Ajay


Edited by ajaymandke, 17 September 2019 - 11:04 AM.

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#11 kimiwaffles

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Posted 18 September 2019 - 11:23 AM

It's in there. See page 38. But does kimiwaffles (hah!) have the Pro model (which uses Synscan) or the non-pro, non-goto model? (I don't even think you can buy the latter anymore but if bought used...)

 

That is actually a very good suggestion. It may just be accurate enough because...

 

The required accuracy depends on the focal length, the length of exposure and whether or not guiding is done. And those all interact. Kimiwaffles specified in another thread (and in her signature) a Zenithstar 73, which has a focal length of 430mm. That's going to be in her favor. In the other thread it was also revealed she is guiding, another plus as far as PA accuracy; one doesn't need to be nearly as accurate as unguided. When guided, imperfect PA causes field rotation around whatever star is selected for guiding.

 

The only variable left is (sub) exposure time. For a standard DSLR (the other thread stated a Canon - I hope it's a fairly recent model) I don't personally recommend exceeding five minutes even in really dark skies. In light polluted skies you will likely not be able to expose that long in any case. IMO exposures of one to two minutes can work in any but the most light-polluted skies, even if they are non-optimal in really dark skies. I think the HEQ-5's polar alignment accuracy using the goto might just suffice for that. The SynScan manual says "Generally, users can get up to 1 arc-minute polar alignment accuracy after repeating this polar alignment process 2 or 3 times."

Wow Alen, thank you for researching my prior posts! This is super helpful. I do have the Pro model, and I looked in my paper manual and found the directions you specified. This will help me a great deal! My plan tonight is to: 1. set my mount up facing north 2. set my altitude at my location on the mount 3. complete the 3 star align and polar polar alignment 4. drift align for better accuracy. Thoughts? 

 

Thanks again :) 



#12 Alen K

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Posted 18 September 2019 - 11:56 AM

Wow Alen, thank you for researching my prior posts! This is super helpful. I do have the Pro model, and I looked in my paper manual and found the directions you specified. This will help me a great deal! My plan tonight is to: 1. set my mount up facing north 2. set my altitude at my location on the mount 3. complete the 3 star align and polar polar alignment 4. drift align for better accuracy. Thoughts? 

I recommend you try to see how low you can get the PA error using the goto procedure (iterate at least twice) and then do a few test exposures at various exposure lengths at whatever PA error you achieved. That will tell you if you really need to drift align. Obviously, if you don't need to drift align I think you would save some time (assuming two or even maybe three repeated goto PA procedures don't take you as long as a drift alignment would).


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#13 artem2

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Posted 19 September 2019 - 08:40 AM

Hello kimiwaffles, I have the same problem, from my Balcony and no view to POLARIS.. I use PHD2 and DRIFT ALIGN.. it is a time consuming matter when you start but the more you practice the quicker you get to align the mount..

 

https://openphdguidi...ment-with-phd2/

 

Best wishes

 

Martin


Edited by artem2, 19 September 2019 - 08:40 AM.


#14 kimiwaffles

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Posted 19 September 2019 - 12:39 PM

Now, using a compass, set your azimuth so that you are pointing to TRUE North (not magnetic as on a compass----if you need to know how to correct a magnetic compass reading to true, just ask).

Would love to hear how to correct a magnetic compass. In my mounts user guide it gave me this formula to calculate my offset to north— does this have anything to do with it?
time zone offset (-7 during daylight savings) x 15 = 105 ; actual longitude (-121, but in the example they drop the - sign and use 121) 121-105= 16. It doesn’t give much information on what to do with that number.
Anyway, your help would be appreciated :)

#15 the Elf

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Posted 19 September 2019 - 02:35 PM

Kimi,

 

watch this video: https://www.youtube....h?v=zQB6UnrTEEM

At 34:00 Forest shows how to do drift alignment without any special program, just a long exposure. He uses BYEOS to take and view the image, but the method just needs an image, no matter how you take and watch it. The first time it may take long, but once you have it, put three markers on the ground where to place the tripod legs and you will be much faster next time. Chris Woodhouse (author of the book "The Astrophotography Manual") suggests to jam some spikes or tubes into the lawn and place the tripod legs in the holes, shown in the appendix of that book.

If you use an auto guider polar alignment is not critical. The guider nails the guide star in place and the polar error cause a very small field rotation. If you are not guiding polar alignment is critical because the error causes a huge drift. I tried the "all star polar alignment" with my AVX (meanwhile happily replaced by an EQ6-R) and it was poor. So I agree to you, use the mounts procedure for a starting point and continue with drift alignment.



#16 kyle528

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Posted 19 September 2019 - 03:36 PM

Now, using a compass, set your azimuth so that you are pointing to TRUE North (not magnetic as on a compass----if you need to know how to correct a magnetic compass reading to true, just ask).

Would love to hear how to correct a magnetic compass. In my mounts user guide it gave me this formula to calculate my offset to north— does this have anything to do with it?
time zone offset (-7 during daylight savings) x 15 = 105 ; actual longitude (-121, but in the example they drop the - sign and use 121) 121-105= 16. It doesn’t give much information on what to do with that number.
Anyway, your help would be appreciated smile.gif

Check here: http://www.magnetic-declination.com/   For San Jose, you need to add about 13 degrees to the east of magnetic north to find true north. I'll also second (or third) the recommendation of PHD2's drift align method. The tutorial here: https://openphdguiding.org/PHD2_Drift_Alignment.pdf   is quite helpful. It may take a few minutes to get the hang of it, but once you do it a couple times it's quite quick, easy, and super accurate. It's my preferred way of aligning and (since I have a permanent setup) checking my alignment periodically. 

 

A couple ideas that may help with future alignment. If you have an area where you can, consider leaving at least the tripod set up. You can carefully take the mount off and set it back on and already be close, just some quick fine tuning. Ideally, you would leave the mount set up all the time, protected from the elements. Many folks don't have this option though. At the very least, find a spot (or spots) in your yard that have the best views of the sky, and once everything is aligned, mark as precisely as you can the positions of the tripod feet, and again this will get you close, and likely just some fine tuning will be needed. I'm not sure how much lighter the heq-5 is than the eq-6r, but I don't think my eq-6 would be all that pleasant to carry in and out for each session grin.gif



#17 Alex McConahay

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Posted 20 September 2019 - 12:43 PM

Kimiwaffles,

That is one weird formula with all those time zones and such. Easier way is to follow the advice already given and look it up (google magnetic north correction for xxxxx and put in name of city or some such thing).

Or if you are using a phone compass, just go to the apps setting and tell it to use true instead of magnetic.

Just remember that true north is in the Arctic Ocean (at the North Pole) and magnetic is south and substantially east on Hudson’s bay.

And where you are changes the correction, and not ina purely predictable way. Furthermore, it changes, and those corrections must be updated every few years. It has changed by four degrees since I first learned it as a kid.

Alex


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