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What method do you Polar Align with?

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#26 orion69

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Posted 09 April 2013 - 11:34 AM

Well, it's all about final result, if polar scope works for you, that's fine.

#27 David Pavlich

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Posted 09 April 2013 - 09:21 PM


In addition I don’t believe that you should do a precise orientation align along with an all-star align. The all-star align has error tolerances that in my experience have always been greater than when I do the Precise Polar scope alignment.

I have never been able to get the All-star alignment to improve on my visual Polar Alignment. However, I can get the All-Star alignment to equal my visual alignment by doing a rough estimate first instead of taking the time to do the precise alignment.


I presume you are talking about ASPA? In that case you must be doing something wrong because you should get much better polar alignment with ASPA compared to polar scope. That may not be noticeable in short subs but over 15min it becomes very noticable.


Show me any unguided 15 minute sub with an 800mm or more scope that doesn't have significant star trails. I don't believe you can do a perfect 15 minute sub unguided with ANY of the Polar Alignment methods. Even with perfect Polar Alignment you will still get star trails after 5 minutes unguided.


My friend, Paul Burke (f29pc), posted a 20 minute unguided image at 2400mm focal length using his MI250. Now, he has a Gurley encoder on the RA axis but none on Dec. Less that good PA shows on the Dec axis. He has it polar aligned to the nth degree and add to that the Gurley encoder and you have the makings of a very good mount that can produce incredible results.

Edit: I dug up the thread Paul posted about his MI250. This.

David

#28 gavinm

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Posted 10 April 2013 - 01:52 AM

Polealignmax or PEMPro pretty much do it perfectly. Never used a polar scope (southern hemisphere) and only use drift alignment for a rough alignment before I use software...and even then, latitude and compass are good enough for software to take over...

#29 Jeff2011

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Posted 10 April 2013 - 09:22 AM

I think part of the problem is that some people have not figured out how to do a precise Polar scope alignment so they just assume it can't be done. Once a few people say that it isn't accurate then it gets the stereo-type of being inaccurate. You have to be extremely precise when doing a Polar Scope alignment for it to work. You also have to be willing to bend down and look through it. In addition you have to be able to shine a light in the front of it and hold your head straight up and down to line it up properly.

All of those things typically make people shy away from doing it that precisely and those are legitimate reasons.

However, that doesn't mean that the Polar Scope cannot be used for a precise Polar alignment without ever doing the All-star align or even a drift align. It can be done. All I am doing is trying to show everyone the procedures for doing it precisely and accurately with the Polar Scope.




Travis,

I for one applaud your post. :goodjob: I often find myself on the unpopular side of a discusion like the 8 inch vs 10 inch Dob question.

I always enjoy reading posts like yours were someone puts in the effort to try to make something work were others have given up on it. I currently do not own a polar scope, but your post is a refreshing change from the typical, don't get one, its is a waste of time.

How does that old Monty Python sketch go. The king thought I was daft to build a castle in the swamp, so I built one anyways.... and the third one stood. :)

Jeff

#30 Footbag

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Posted 10 April 2013 - 11:04 AM

I have the AP PASILL4 and only give it a so-so rating. When I rotate it, I get a slight bit of movement on the centered object. The adjustments seem a bit dangerous. If the RAPAS continues to get good reviews, I'll pick one up eventually.

My favorite PA method is PHD drift method. It probably takes 20m. But I've also been using the AP Quick Drift method. There are a few more things that can go wrong, but the results are amazing.

mpgxsvcd,
Have you tried calibrating your images with darks? I'm wondering whether the noise and hot pixels will calibrate out.

#31 Raginar

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Posted 10 April 2013 - 11:08 AM

Footbag,

Have you tried PEMPRO's polar alignment wizard? It's pretty good too.

To the others, I don't think a polar scope or one of the software alignment routines is going to get you to 15 minute unguided subs. But they do put you in a position to perform a simple drift alignment that will allow you to perform within the specs of your mount. Some are better than others... but you can get your polar alignment that you can do unguided photography. Just depends on the mechanics of your particular mount and the image scale of your CCD/telescope combination.


#32 mpgxsvcd

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Posted 10 April 2013 - 11:39 AM

I tried comparing my visual Polar Aligning with the Polar Scope to the All-star aligning last night. The first image below is a 4 minute exposure with the Aligning done visually with the Polar Scope only.

There were no stars that were directly horizontal or vertical so you can see that my tracking was not good for this setup.

The second image below was taken after I did an extremely precise All-star Polar Alignment with my Cg-5 mount. As you can see tracking is still an issue with that image. All it did was change the angle of the drift but it really didn’t decrease the magnitude of it.

This is why I say that if you are able to achieve a very good Polar Alignment with the scope then just leave it alone. Using the All-star Alignment will not improve on a “Precise” visual alignment. However, if you do a rough visual alignment then by all means do the All-star alignment because it definitely can correct most of your original error.

In my experience you can get roughly the same results by doing a very precise visual Polar scope alignment or an All-star alignment. However, doing a good visual Polar Scope alignment requires much more attention to detail than doing a good All-Star alignment.

Anyone can do a good All-star alignment. Not everyone will have the patience to do a good visual alignment. Once you get enough practice at both methods they take about the same amount of time to do.

4 minutes unguided. Not a very precise Visual Alignment because no stars were horizontal or vertical.

Attached Files



#33 mpgxsvcd

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Posted 10 April 2013 - 11:39 AM

I have the AP PASILL4 and only give it a so-so rating. When I rotate it, I get a slight bit of movement on the centered object. The adjustments seem a bit dangerous. If the RAPAS continues to get good reviews, I'll pick one up eventually.

My favorite PA method is PHD drift method. It probably takes 20m. But I've also been using the AP Quick Drift method. There are a few more things that can go wrong, but the results are amazing.

mpgxsvcd,
Have you tried calibrating your images with darks? I'm wondering whether the noise and hot pixels will calibrate out.


Yes darks definitely works great with the GH3. I was just trying to show that you can track fairly well with the CG-5 even without guiding so I just attached the cropped out of camera image. It cleans up very well if you either do in camera darks or stack with darks in DSS.

4 minutes unguided after precise All-star alignment.

Attached Files



#34 Peter in Reno

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Posted 10 April 2013 - 12:00 PM

In order to get round stars with 15 minutes unguided, I believe you need a pointing model that will take care of refraction and other irregularites in the sky. The only time the stars move at sideral rate is at the Meridian +/- 1 hour (or less) of each side. Even with perfect polar alignment, I don't think you can get good unguided results at least 1 hour from the Meridian without a pointing model.

For example, one night I was finished with polar alignment and slewed to a star in the East which was nearest to my target DSO for imaging, centered the star with imaging camera. The sky was not dark yet so I went insdie and watch TV until the sky got darker. 30 minutes later, I went outside to check on the star, the star drifted in RA instead of Declination. I wondered why drift in RA and later figured out that my mount was tracking in sideral rate and the star was about three hours from the Meridian. If I had pointing model already done, the star would have remained or very close to the center. Drift in RA instead of Declination was an indication of good polar alignment because bad polar alignment will show drift in Declination. If the star was near the Meridian, then the star would have stayed closer to the center of my camera.

My setup is always portable, so I think pointing model would have been too time consuming. In addition to good polar alignment, autoguiding should be good enough for any mount. I would not try to work too hard on getting good images unguided. You are better off to add a guidance system using guide scope or Off Axis Guider and you will be happier using autoguiding.

My method of polar alignment is Astro-Physics (A-P) Quick Drift Alignment using A-P Meridian Delay found in all A-P mounts. With experience, it takes less than 15 minutes and it's quite accurate that I can image at 30 minutes sub-exposures, autoguided of course. I also have A-P polar scope which is the same as Losmandy polar scope and found it to be inaccurate for long exposure imaging. It's good enough to get started and help to finish accurate polar alignment quicker.

Peter

#35 mpgxsvcd

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Posted 10 April 2013 - 12:27 PM

These are definitely the type of posts I wanted to see. I just want to know what works and what doesn’t and what works for some people may not work for others.

I totally agree with the sentiment that guiding is the optimal solution. However, I simply don’t want any wires attached to my mount. My camera allows me to do everything wirelessly and I would like to keep it that way if at all possible. If someone made a standalone auto guider that didn’t require a second larger scope I would be willing to pay a lot for it.

I tried the Celestron NexGuide Autoguider with my finder scope and it simply didn’t work. It couldn’t find any stars with the small finder scope. It looks like the scope they recommend for use with it is too heavy for my mount with my rather heavy AT8IN.

Does anyone have a good auto guider solution that doesn’t require wires or another heavy scope? Is there any way to use the NexGuide Autoguider off axis?

http://www.amazon.co...VRUGRG/ref=s...

http://www.amazon.co...n/dp/B004IB2...

#36 Footbag

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Posted 10 April 2013 - 12:36 PM

There aren't many fans of standalone guiders here, and I only know that I've seen a lot of people send them back. Is it the wires you don't want or the laptop?

I don't know anythign about them but, TS sells the LVI guider. That may allow you to go laptop-less, but not wireless.

#37 mpgxsvcd

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Posted 10 April 2013 - 01:21 PM

There aren't many fans of standalone guiders here, and I only know that I've seen a lot of people send them back. Is it the wires you don't want or the laptop?

I don't know anythign about them but, TS sells the LVI guider. That may allow you to go laptop-less, but not wireless.


It is the laptop that I want to refrain from using. I don’t mind the wires as long as they move with the scope. I have wires from the mount to the scope and from the scope to a dew fan. I just don’t want wires that go from the scope/mount to anything that is not moving with the mount.

#38 HowardK

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Posted 10 April 2013 - 01:32 PM

SBIG. SG4

Stand alone guider...set up one time with laptop for focus then no more laptop needed.

Comes with its own tiny lens...mine is attached to a tiny 50mm hutech scope.

#39 orion69

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Posted 10 April 2013 - 02:01 PM

@mpgxsvcd

You can't evaluate precision of polar alignment by doing unguided subs. Your mount is simply not good enough for that. Even with high end mount you'll need precise star model and absolute encoders for long unguided subs and that is not achieved with polar scope.

I'm not saying that polar scope is useless, of course not. But for longer guided subs in most cases you'll need better PA (drift is the best).
I can say from personal experience that you can get 30min guided subs with ASPA using OAG. As for stand-alone autoguider I would not recommend it. Best option is to get OAG for subs 15min and longer.

Forget unguided imaging.

Cheers

#40 mpgxsvcd

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Posted 10 April 2013 - 02:33 PM

@mpgxsvcd

Forget unguided imaging.

Cheers


Sorry I don’t agree with that sentiment. I understand that most people require guiding because their focal lengths are too long and their focal ratios are too large. That is precisely why I bought the scope I have.

I don’t need to track for super long durations. In fact I start to blow out the sky in my back yard in about 8 seconds at my max usable ISO(6400). At 4 minutes I have to use my minimum ISO(200) to avoid blowing out the sky. Going any longer than that would be of no benefit to me.

However, I would like to be able to accurately track from 1-3 minutes without guiding. I have found that I can achieve that with the Polar Finder Scope and I thought I would share that with anyone else who would like to do the same.

In my experience things like wind and uneven cooling affect my tracking more than the error in my Polar alignment do if I have done a precise Polar Alignment.

As I have said before. I am not trying to say that using the Polar Finder is the best method. However, if you choose to only use a Polar Finder then trying to line up stars horizontally or vertically will help you get enough precision to do 2-3 minute subs.

One thing I haven’t seen mentioned here is the use of apps like “Polar Finder” to aid in aligning with the Polar Scope. I just bought the app for about $1 for my Android phone. It looks good so I am going to try it tonight.

Does anyone else use this app instead of the diagram’s of UM inscribed on the Polar Finder?

It is important to remember that you have to set the image orientation to “Telescopic” in the app to accurately find out where Polaris should be in the finder scope. However, that also means that UMA will be on the opposite side of where it appears to be when you look at the etching on the Polar Finder.

If you use the app it is best to just ignore the UMA etching in the Polar Finder altogether.

Ideally you want Polaris to be either vertical or horizontal even with the app because estimating angles in-between those is much more difficult. I really wish that the polar finder had the 15 degree increment marks like the app has. It would be so much easier to be more precise if it did.

http://www.appbrain....ead.polarfinder

#41 Raginar

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Posted 10 April 2013 - 03:06 PM

Travis,

What he's trying to tell you is that it is very difficult for very experienced people to do what you're asking. Your mount doesn't have the mechanical fortitude to perform in a manner you think it can. If it did, why would most of us APers spend several thousand dollars on our MI250s, G11s, and AP mounts?

The real problem is your mount is overloaded. I had trouble with my AT8IN on my CGEM. I imagine you will run into similar issues with your CG5.

I know, it sucks. You could try hypertuning, but you're shining a *BLEEP*. A *BLEEP* that works with light weights (which your AT8IN isn't) and widefield refractors. But a *BLEEP* nonetheless.

Good luck!

Chris

#42 mpgxsvcd

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Posted 10 April 2013 - 03:30 PM

Why would most of us APers spend several thousand dollars on our MI250s, G11s, and AP mounts?


That is a great question. So what did make you choose one of those mounts over a less expensive model? Was it because someone told you it couldn't be done with anything less or because you tried other mounts and no matter what you did they wouldn't meet your expectations.

Sure we would all love to have those mounts that you listed. However, some of us simply do not have the means to purchase them. Instead we make compromises and purchase lesser mounts and then spend extra effort on optimizing them to get the results we are after.

In the end we both are happy with our equipment. What gets me is when people say "It can't be done" and what they really mean is that "It is really hard to do".

#43 Footbag

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Posted 10 April 2013 - 04:10 PM

However, I would like to be able to accurately track from 1-3 minutes without guiding. I have found that I can achieve that with the Polar Finder Scope and I thought I would share that with anyone else who would like to do the same.


If you are happy with your results, then nobody can tell you otherwise. I suspect that as you improve, you will look back at the images you took and not be as impressed as you were previously. This hobby is a moving target. As you improve your images, you realize there are other aspects to improve.

I switched to the Mach 1 because my last mount couldn't do what I wanted. Track 30m guided for narrowband @ 2032FL. At that point, I knew my equipment very well. It wasn't somebody telling me it couldn't be done, it was me trying it over and over. The new mount makes it easy.

As far as the "it cannot be done". In this hobby, one can do anything. That's not to say everyone would be happy with their results. Keep in mind, most imagers throw away their images that show drift, but not all. ;)

#44 psu_13

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Posted 10 April 2013 - 06:51 PM

Here is my experience with mounts.

I started out trying to use a Mallincam on my 8SE alt/az mount. Here is maybe a 20-30 second frame from that

http://www.flickr.co...157629128096583

Notice how the stars are already trailing.

Here is a shot I look later on after I moved the telescope (an 8inch SCT) to a CG5

http://www.flickr.co...57629128096583/

This is at around a minute. I found that with the scope at F5 (1000mm focal length) I could get 60 to 90 seconds out of the CG-5 without a lot of jumpiness. I always used the all-star polar align scheme.

As a comparison here is a shot at 300mm focal length (a refractor) at almost 2min

http://www.flickr.co...N00/6788830992/

After using the CG-5 for a while I decided that I was serious enough about taking pictures and had the money to get a "serious' mount. More on what I think "serious" means later. But I bought a Mach-1. Here is a stack of 2min exposures with the Mach-1 at 1200mm focal length:

http://www.flickr.co...N00/6835654848/

They register well enough that stacking worked. And there is less trailing than in the short focal length shot above. This is why people buy expensive mounts. They are mechanically more accurate, smoother, and more reliable than the cheaper stuff. This is not to say that you can't make the cheaper stuff work, of course you can. It is just to say that the expensive stuff does have value and it makes everything easier.

I'll also say that even having spent thousands of dollars on the Mach-1, I never managed to do better than about 3min unguided without the stars trailing too much. Here is such a frame, also at 1200mm

http://www.flickr.co...57629550839360/

There is enough jitter in even the best gear train to require that you do some kind of guiding or other computer-enhanced tracking (modeling, encoders, whatever). For the Mach-1 I have used the same meridian flip based scheme at Peter from Reno, and more recently PEMPro. My experience with the mount pretty much matches his.

Later on I finally decided I had to investigate guiding, so I bought an SBIG camera with a guider in it. Here's 4 minutes guided without even thinking too hard. Note how everything is rock solid:

http://www.flickr.co...57631169684214/

I sympathize with the desire to keep things simple, but we are talking about holding a camera and telescope exactly in sync with the earth's rotation for hundreds of seconds. You can't buy that with just polar alignment and a relatively cheap mount IMHO.

My longer thoughts about mounts:

http://atelescopeint...1/05/mount.html

and the Mach-1

http://atelescopeint...-for-money.html

Oh, and, FWIW, the control box of the Mach-1 does not move, so you can hook wires up to it without worrying about it. :)

Cheers and good luck

#45 jsines

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Posted 11 April 2013 - 10:58 AM

Hi Travis: try using your camera to assist you in getting a better polar alignment once you have used your polar scope. It is a modified drift alignment which is best explained by this link: http://www.observato...ent_CCDv1-1.pdf
A camera such as yours is just as capable to do this method.



Question on this method - I've been trying it for a few weeks with good results, but I'm not sure I'm doing it right. Should I polar align, then find a star, then turn on sidereal tracking, then image and move the scope east/west at the lowest speed? Or, should I keep sidereal tracking off?

I'm doing it with tracking on right now, and I'm getting spot-on solid lines every time the first time, with up to 2 minute exposures. I'm wondering if I'm doing something wrong, or if I'm doing something right. :p

#46 psu_13

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Posted 11 April 2013 - 12:48 PM

Since you are moving the mount by hand it doesn't really matter if it's tracking or not. The sidereal tracking only tracks in RA anyway, and you are using the scheme to look for drift in DEC.






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