Polar Align

[Rocket Pooch]

Hi,

I used polar align last night for the 1st time, I bought as license a year ago, but you know what its like.

It seems to work ok if you know where the setup stars are .  My goto's were bang on after I did a sync in EQ Mod.  I was observing at 2 meters FL and M27 was dead centred in the cross hairs on the test eyepiece 26mm (76x mag), then a slew to Alkaid, bang on, M57 bang on, then back to NGC891, again smack in the middle (not an easy visual target).

So I think its a good tool for £12.

However, it does rely on you getting the scope pointing to the home position correctly, so you need to do some iterations of alignment.

Chris

[Les R]

Polar align? Wassat? (got a link?)

I shocked myself last night with a first time 3 star alignment. But I still need to work out the best way to be sure of an accurate "home" park! But hey, it's improving!

[Carole]

Was going to reply to Les' question, but not getting drawn into another hijack.

Carole

[Rocket Pooch]

http://www.alignmaster.de/

[The Thing]

Hi Chris,

I use AstroTortilla to do my polar alignment. It's sort of like drift alignment but more mathematical. It's also free

I do a rough align the use it's feature which plates solves an image from your capture program( many supported) or a screen grab (very versatile), then AT knows exactly where your pointed. It doesn't matter exactly where as long as E/W or close to the meridian depending on if you are working on the altitude or azimuth position of the mount head.

AT then moves the mount a known distance and solves another plate. It knows where the mount should be pointing, and it now knows exactly where it is really pointing, it does some conic maths stuff and calculates the error in degrees up/down or east/west. This takes 60 seconds. You then twiddle the knobs and do it again until you are happy with the alignment in that axis, then do the other. I get to within 45 arcsecs in about 10 minutes with the original knobs on an HEQ5. Never that got close with the polar scope.

AstroTortilla also makes finding targets a breeze, you GoTo the target, plate solve it, AT then issues a sync to EQMOD where you are rally pointed and then re-slews the correction. You are always bang on target and your point model is refined each time. Lovely.

Les -  Google it. It's important to get it right. Also home parking is unimportant unless you have a permanent setup.

[Carole]

Also home parking is unimportant unless you have a permanent setup.

Agreed to a certain extent, but I think returning the mount to the position you started at is a good habit.  I didn't know about this when I started and just used to switch off where I left off and had no end of alignment problems in those early days.

Carole

[Carole]

Chris have you got a link to polar align?
No end of options come up when I google.

I've tried Alignmaster as well and was thinking of getting it, but would like to check out this one too.  Is there a try it out option?

Ignore
Just read the renamed post at reply 3.

Carole

[Les R]

http://www.alignmaster.de/

Just had a look at the video and it looks very good. Actually, thinking about it, I had to forget using EQMOD when I first tried alignment at home with the HEQ5 as I couldnt work out what I needed to do to get started and ending up using the handset.

Looked very good, though in the example he was using a camera and a cross hair, so not sure how to do that optically (which I assume to get it accurate "that looks about right" probably isnt accurate enough?

[Rocket Pooch]

Hi Les,

I used an eyepiece with cross hairs in it, it worked ok.

Chris

[Mike]

I also use Alignmaster. I like the fact you can use eyes, webcam or CCD to view the star and it gives you options as to which stars to use. Really easy to use, quick and works extremely well.

[Carole]

I could centre the star when I did it but the star was lower down rather than on the cross.  Some-one suggested the mount was not quite level enough.  So should I tweak the pier plate slightly or tweak the up/down bolts.  As far as I could see it was level, bubble was in the right place. 

Any thoughts on this?

Carole

[MarkS]

I have mathematical concerns about this.

I think these approaches will give you a reasonable approximate alignment (sufficient for most imaging) but also a false of security that you are very accurately aligned.   If it is only using 2 stars it cannot calculate and account for cone error (the error caused by the scope not being exactly perpendicular to the main axis of the mount) or flexure error.

I much prefer a polarscope - much quicker and possibly more accurate.  Beyond that, drift alignment or an approach that involves mapping numerous stars across the whole sky.

Just my 2 pennyworth.  I'm happy to be proved wrong ...

[Mike]

I don't know if it makes a difference Mark but it uses two stars that are very far apart and you are supposed to reiterate the procedure over and over until no more adjustments are necessary (Although for field imaging I just get it close enough, which is usually about 3 or 4 iterations. For a permanent set up it would be worth doing it till perfect).

[MarkS]

The number of iterations makes no difference.  You will still end up with an alignment that is incorrect by approximately the size of the cone error + flexure error + mirror flop error.  However, if those errors are tiny then you will have a very accurate alignment.

Unless the polar alignment software documentation tells you that it is also correcting for cone error etc then it's best to assume it doesn't.  If it is using only 2 stars then it's impossible to correct for these.

As far as I can see, accuracy can only be guaranteed by drift alignment or whole sky mapping.

[Rocket Pooch]

I have mathematical concerns about this.

I think these approaches will give you a reasonable approximate alignment (sufficient for most imaging) but also a false of security that you are very accurately aligned.   If it is only using 2 stars it cannot calculate and account for cone error (the error caused by the scope not being exactly perpendicular to the main axis of the mount) or flexure error.

I much prefer a polarscope - much quicker and possibly more accurate.  Beyond that, drift alignment or an approach that involves mapping numerous stars across the whole sky.

Just my 2 pennyworth.  I'm happy to be proved wrong ...

Hi,

Also, you can setup your scope properly on the mount that help.  With cone error the same issues would apply with drift alignment for goto's.  You should give it a go its quite good.


EQMod was sync'd with 4 points on the sky (normally), that deals with the other issues.

Chris