QHY PoleMaster

[Shelster1973]

Am rather tempted by getting this to help with my PA, but feel I may not get the full use out of it as I am using a fixed pier.

I do take the head off the pier a couple of times each year for maintenance of head and pier, so would get used then I suppose....one other option would be to loan out the camera to tohers who want to use it and try and get some funds back that way....

[iapa]

Thanks @StuartJPP

 

[animaal]

Is it necessary to have an unobstructed view of the sky below Polaris? If so, how much of the sky? I have a view of the star with a roof directly below it

[PeterCPC]

You need to be able to see both above and below Polaris because you need to align several stars in the area with a template as part of the process. See the post on page 2 of this thread for field of view.

Peter

[Mav359]

I finally got to play with mine during the week and i have to say i am so pleased, having watched the earlier video i knew what to expect but it was very simple anyways & the whole thing was done in a few minutes, then did a star align and away she went. In less then five minutes i had polar alignment that allowed me expose unguided for just under 5 minutes before i just began to see faint star trails. Thats 3mins better then any previous effort.

I was fighting fires during the week, a dodgy cable was preventing pulse guiding so i couldn't use PHD or Labs to put a number against how good or bad the PA actually was & along with dodgy collomation of my Hyperstar and then slightly unbalanced mount. I was only putting the OBs back together but all those niggles have been fixed.

Very pleased, even knowing that my setup wasn't quite right 100% i was getting good results and knowing that i can re-check my PA in a matter of minutes at any point now is just bliss.  Now that everything is 100% i'm really looking forward to the skies clearing and just going out & have a proper test, i'll have another go (just because i can) and then really push the exposures to see how far i can get, not to mention put a number against the PA

Absolutley worth every penny, THE BEST TOOL i have spent money on since buying the scope.

[StuartJPP]

On 17/03/2016 at 16:43, animaal said:

Is it necessary to have an unobstructed view of the sky below Polaris? If so, how much of the sky? I have a view of the star with a roof directly below it

A similar question was asked on CN and I will answer it here too...

You basically need the following FOV around Polaris (the red square), a little less will do, it depends on the time of day and the position of Polaris and the alignment stars (LST). They can be in any position rotating around the NCP. You may need some extra space around this for initial error and correction, but if you place Polaris in the middle of the screen you shouldn't be too far off to begin with.

If you can only just see Polaris peeking over the roof then I think you will struggle, especially at certain times (not so bad in the 1st image but more so in the 2nd).

At point 't' in time.

 

12 hours later.

[knobby]

 Polaris will be very jumpy on screen if its near the roof too, workable but erratic.

[animaal]

12 minutes ago, StuartJPP said:

A similar question was asked on CN and I will answer it here too...

You basically need the following FOV around Polaris (the red square), a little less will do, it depends on the time of day and the position of Polaris and the alignment stars (LST). They can be in any position rotating around the NCP. You may need some extra space around this for initial error and correction, but if you place Polaris in the middle of the screen you shouldn't be too far off to begin with.

Thanks, I think I get it. All six alignment stars must be visible. The farthest from the celestial pole is 2UMi, which is approx 3 degrees, 40 minutes from the pole. So if there's that much clearance between the roof and the pole, we're good.

 

 

[alexW]

I have a couple of things to add to the discussion of the PoleMaster and to polar-alignment in general. First, believe it or not, measuring alignment error with a procedure that interprets drift is fraught with difficulties. Cross-talk between the errors in azimuth polar alignment and the altitude polar alignment make it difficult, probably impossible, to make a single measurement that reveals total polar-alignment error, in general. Drift alignment works because it can iteratively reduce alignment error, pass after pass. If a single measurement could quantify alignment error, then why do we have to make more than one drift measurement at all?

Second, the single thing that accurate polar alignment adds to imaging is the reduction of image rotation. A program like PHD2 can keep the target star round and untrailed. But poor alignment can make the other objects in the field show rotational paths around the guide star. Think of Alt-Az mounts, like the big one available from PlaneWave or that operate in professional observatories. Obviously, they have no polar alignment. Yet they can take very long exposures. WHY? because the have image de-rotators. Image rotation is the only down side to imaging using a mis-aligned mount. For modest exposures over most of the sky, image rotation itself is insignificant even with shoddy polar alignment.

While being preachy, I'll add one more thing. The PoleMaster has pixels covering about 1/2 arc minute. By the Nyquist-Shannon theorem, we would expect alignment qualities not better than 1-1.5 arc minutes. Throw in some uncertainty in matching the overlay to the star field and the creep when mount knobs are tightened, and one is probably lucky to reach 3-5 arc minutes. Reports of alignment qualities as low as 1.5 ARC SECONDS, must be regarded as indicative of the general inadequacy of current alignment-error measuring techniques, and not at all indicative of true values.

 

Alex.

 

[StuartJPP]

What amazes me the most about some of the comments from people using PoleMaster are the ones that indicate that those users were obviously not polar aligning properly prior to using a PoleMaster. PoleMaster isn't more accurate than (a proper) drift alignment, and probably only on par with or perhaps a slight bit better than a decently collimated polar scope. It doesn't perform miracles.

With regards to your comments Alex, PHD2 is not aware that you polar aligned using PoleMaster, a polar scope or performed a drift alignment, so the polar alignment accuracy reported by it (or others) has to be taken with the same pinch of salt (which you noted). I posted the results previously using PHDLab, does it calculate it correctly? I don't know but it is a reference point for others to measure against. With respect to the error introduced by tightening of the knobs, surely that applies to either drift or PoleMaster alignment?

But I take your point, if the focal length was 130mm (like on their miniGuideScope) then it would be a lot more accurate (~6 arcseconds per pixel). The choice of 25mm was most likely done to get a decent FOV that was easy to identify Polaris in the star field and you can basically point it in the general direction and Polaris will be visible and obvious.

It is much more convenient to use than either a polar scope or drift aligning, that is where I and many see its value. It is certainly accurate enough for my focal lengths, it may not be for others.

 

[themos]

6 hours ago, alexW said:

 If a single measurement could quantify alignment error, then why do we have to make more than one drift measurement at all?

Because drift alignment is inherently only sensitive to one component of PA error, it depends on where the chosen star is relative to celestial equator/meridian. When we didn't have the technology to plate solve what we see or to insert markers in what we see, drift alignment was a good choice. Not any more.

[Mav359]

All i know is that with the PolarMaster i got polar aligned in under 5minutes to a point better then i had achived previously and that coupled with guiding is more then good enough, i had one chance last night  and i got to 20min exposure without star trails before the cloud rolled in, another first for me.

The other thing to remember its great for those us us that don't have unrestricted views of the skies to do an accurate drift alignment.   Its quick, easy and produces results that (for me at least) are good enough. For me the time it saves alone makes it worth while

[nightster]

Another aspect of this that I hadn't thought of was my personal stress level.  Looking back as I attempted subs longer than 600s (where I suspected the Field Rotation issues to appear) I would get more and more frustrated trying to get good PA before I began a run. After spending more time then I wanted drifting, using PHD2 drift or one of the other software solutions, I would then feel rushed when moving to the next step. Then I spent more time than I wanted trying to manually focus, stress levels increased again. At this point if something went wrong with PHD2 calibration I was no longer thinking clearly and would make more mistakes. So then the really important stuff would suffer, framing might be off or maybe I forgot to refocus for a filter change or temp drops. A host of issues would pop up and my stress would keep me from making good decisions.  This device actually had quite a calming affect for me as it demystified one of my ongoing problem skills, good PA. A Moonlite and Stepper helped me with the other stress inducing task.

[PeterCPC]

Version 120 is now on the QHYCCD website.

Peter

[George 47]

I hate Polar Alignment. Yes, I hate Polar Alignment.

So having seen these good reports (and those on CN) I bought a Polemaster from RVO with the IeQ 30/45 adaptor for my G-11. It fitted the screw thread with no problems.

And guess what a clear night last night.

So I set it up and ran the software to get used to it without adjusting the mount. I had used a compass to find North. It was really simple and easy. So I re-ran it but this time adjusting the mount. The software guides you through the whole process step by step. It took 5 minutes and was very easy to do. As I was using the ZWO for Jupiter imaging I ran PHD2 to try and measure the errors. I set up the drift alignment routine and let it run for 25 mins to get a reasonable baseline. It reported errors of 0.23 arcminutes. I have never got that low an error with a polarscope including the RAPAS on my AP900. The errors on the PMX using TPoint with a 50 point model are worse (but TPoint may be more accurate) and that took hours.

So for me this is a real boon because of the speed and ease of process. Hopefully the adaptors for AP900/PMX will be coming soon.

I recommend it.

[alexW]

Just a little perspective on polar alignment accuracy. Say your mount has about 200mm's from the pivot (adjustment) point to the N. end of the polar axis. That's about what my EQ6 has. Say you want to reach the alignment accuracy claimed by QHY: 30". OK, a little trig shows that you have to adjust the height of the front end of the polar axis to within 0.03mm. If you want to claim you have accuracy at something like 5", than that means you were able to adjust the height of the front of your polar axis to within 0.005mm. Wouldn't that be nice? But, everything from sinking a leg into the grass to differential thermal expansion are against you; not to mention the pitch on the adjusting screws and the backlash when they are tightened down. So, what might reasonably be predicted for the level of accuracy most of us can expect to obtain AND RETAIN, particularly for a portable rig (and that's the domain of the PoleMaster)? My guess is somewhere around +/- 1/2mm--optimistically--and that's about 1/4 degree. Obiter Dicta: PHD's (and other drift-align tools I'd guess) estimates of alignment error are unreliable or misinterpreted.

Happy to be persuaded otherwise by a strong argument countering this simplistic analysis. It would have to include evidence that adjustments of polar-axis elevation can be made, and retained, down in the 10ths or 100ths of a mm!

[Davey-T]

Tricky thing to do anyway, considering Polaris is something like 430 light years away and you're trying to poke it with a long stick stuck through the RA axis, doesn't take much error to miss it 

Dave

[George 47]

Alex,

The issue for me was I can get a certain accuracy with a polarscope. Using that alignment I used PHD2 which reported a certain polar alignment error.

Using the Polemaster and PHD2 I get lower reported errors.

In an absolute sense it does not matter as long the Polemaster does the job (better?) and far more quickly. I had to add a note of caution for the TPoint comparison as I used  2 very different ways of measuring the errors. Overall though if I can let a 1.1m focal length scope run for 25 minutes and only get 1 pixel drift in the worst part of the sky then for me, that will do.

I agree with your main point though as some of the reported numbers are becoming unbelievable and a little irrelevant as the aim is to get very close polar alignment and minimise errors and drift. That is the key thing not the absolute value of the numbers.

Despite that I still regard the product as a good one that does the job quickly.

[wigggyy]

Used my polemaster last night and really made things very easy a great piece of kit

[themos]

20 hours ago, alexW said:

Just a little perspective on polar alignment accuracy. Say your mount has about 200mm's from the pivot (adjustment) point to the N. end of the polar axis. That's about what my EQ6 has. Say you want to reach the alignment accuracy claimed by QHY: 30". OK, a little trig shows that you have to adjust the height of the front end of the polar axis to within 0.03mm. If you want to claim you have accuracy at something like 5", than that means you were able to adjust the height of the front of your polar axis to within 0.005mm. Wouldn't that be nice? But, everything from sinking a leg into the grass to differential thermal expansion are against you; not to mention the pitch on the adjusting screws and the backlash when they are tightened down. So, what might reasonably be predicted for the level of accuracy most of us can expect to obtain AND RETAIN, particularly for a portable rig (and that's the domain of the PoleMaster)? My guess is somewhere around +/- 1/2mm--optimistically--and that's about 1/4 degree. Obiter Dicta: PHD's (and other drift-align tools I'd guess) estimates of alignment error are unreliable or misinterpreted.

Happy to be persuaded otherwise by a strong argument countering this simplistic analysis. It would have to include evidence that adjustments of polar-axis elevation can be made, and retained, down in the 10ths or 100ths of a mm!

Good point. It will be interesting to measure my PA after a long imaging session and see what happened to my initial 1-arcminute error.  We all know what happens to focus after a few hours, don't we?

[George 47]

3 hours ago, themos said:

Good point. It will be interesting to measure my PA after a long imaging session and see what happened to my initial 1-arcminute error.  We all know what happens to focus after a few hours, don't we?

True, especially in the field. Even in an observatory I suspect there will be settling. However, the key is that it looks like we are getting close to having a polar alignment method that may be better than what is needed or better than the mechanics of the scope's adjusters.

On that, if you look at the Paramount manual (and the Astrophysics ) then the scales they have on their azimuth adjusters have minor scales that represent 1 arcminute between lines. Looking at the scales I would guess you could adjust them to a half way point so 0.5 arcmins looks feasible. In fact it is the TPI of the thread that would control what is possible plus the engineering of the adjuster. So some of the numbers are feasible.

Also whilst I appreciate that if the scale of the camera is 0.5 arcmins per pixel,  does that represent the limit of the system? If the star is spread over a set of pixels and the software uses the centre of weight method to identify the centroid to a precision of 0.1 pixels then it should be possible to measure intermediate values.

[Mav359]

the point of this system is ease of use & time......

Are there more accurate methods, maybe. With more time can you get better results, probably but if you are out in the field or tear down every night then this system just works, at least it does for me.  I go out, PA with it and in 5mins & guiding i and getting upto 25min subs, better then i have ever previously gotten & i don't feel that my subs are any worse at the end of the night.

The point of the thread is the polemaster and whether its any good, for me its a big big yes and i think anyone who has got one will agree. I think the majority of people just want to be getting the most AP out of their limited time & skies

 

[StuartJPP]

As mentioned above, I am not interested in actual polar alignment error/accuracy as long as it is better than other methods using the same measurement method.

There are wild claims in astrophotography, occasionally bordering in pseudo science, and to me the only proof is in the unadulterated full sized subs, which hardly ever get posted.

The PoleMaster is better, easier and faster for my imaging rig, it may not be for all though.

[PeterCPC]

Version 130 is now on the QHYCCD web site http://www.qhyccd.com/PoleMaster.html

Peter

[PeterCPC]

I have noticed that, when you do the precise PA, the image of the two circles (red/green) is not exactly the same between the image in the PA panel on the left of the screen and the magnified view you get at the top if you hover the mouse over the 2 circles.

I raised this issue on the QHYCCD Forum and have been told that you should use the smaller image on the PA panel (the one on the left) rather than relying on the magnified view at the top of the screen. They say that this will be more accurate.

Pity, I found it much easier using the magnified image at the top.

I hope that all makes sense as it's difficult to describe.

Peter