Polar Alignment using Polar scope

[strongmanmike]

I have mentioned this before but I just wanted to provide an example of why this might be a method for those of you with polar scopes to try.

Back in 2005 I carefully drift aligned my NJP mount with Starfire and then made a drawing and memorised the position of the cross hairs in relation to the other field stars in teh polar scope. I have since adjusted for precession (approx)

On Thursday night I positioned the cross hairs to the SCP position I know in the star field, as usual. I hadn't tested the accuracy of this polar alignment method for a while.. so I put a guide star on the cross hairs at 600mm FL and went inside for dinner (45min?), when I returned I was delighted to see the guide star had only drifted about 2 pixels and in RA only...not bad for just eyeballing through a polar scope.

Who needs Polar Align max etc?? If you have a polar scope (all it needs is cross hairs, other circles and Polaris positions etc can be ignored) I recommend you take the time to get familiar with your polar scope field, then in the future and provided you can see the SCP, you can be very accurately aligned in minutes - very useful for those who are portable :thumbsup:

Cheers

Mike

[h0ughy]

i am impressed - not for the fact that the polar scope has proved to be almost spot on but the fact you can see the SCP in Newcastle or were you elsewhere?

[Barrykgerdes]

The south celestial pole through an eyepiece FOV 30Arc minutes. Roughly a 10" SCT with a 26mm Plossl eyepiece. Taken from stellarium
but quite close to what I actually see.

The first is the J2000 view which I used originally. The second is the J2011 view showing the precession of 11 years

Barry

[multiweb]

Sounds real good Mike if you know where to look. I can't see anything south from where I am because of LP which makes using my polar scope very very hard. :shrug:

[gbeal]

Darn Mike, you have me worried now. I've been at this game longer than most and my best polar alignment routine has so far been roll it out and line it up roughly with a tree that is about a kilometer away across the paddocks. When I got real flash I tried drift aligning, but not with the steely determination it deserved.
So, I am ashamed to say, I couldn't tell you where the stars should be in the polar scope, even though I do have one (I think?) in the NEQ6.
Maybe I should take a look. I have had the mount head off the pier a while back so it could be anywhere.
Gary

[strongmanmike]

Those charts are good Bazza. When I first did the accurate drift align in 05 the location of the SCP was closer to the position in the first map ie I used to point the cross hair to a pioint that made an equilateral triangle with the two doubles (both appear singular through my polar scope though), I now point to a position that forms a slightly flattened equilateral triangle with the two doubles...hence, looking at your charts, why I get so close :thumbsup:..I think by about 2030 the SCP will sit perfectly between the two double stars, this should make for very accurate polar aligning using this method and very easy too.

Mike

[strongmanmike]

The two double stars in Barry's maps ( I see them as two singular stars though) are indeed hard to see form mums place in New Lambton (especially with a moon up!), but I guess I am so familiar with them now it is still a good method, as evidenced by the original post :)

Mike

[strongmanmike]

If you drfit align you must know here to look ie look through the polar scope after the drifting shows you have good alignment..? :shrug:..if you can't actually see the area of the SCP (trees, house etc) then yes you are unable to use this method. Would be very quick when at Wiruna for example, the reference stars are very easy to see from a dark sky, took me litterally a minute or two to get within 2' of the SCP when I last visted Wiruna with my gear :thumbsup:

Mike

[strongmanmike]

Well, if you need accurate PA and want it quick each time here's a method to try next time you are out ..and have the mount back together :thumbsup:

Mike

[strongmanmike]

What's the grid ring spacing on these charts in arc min..?

Mike

[multiweb]

You're right. I have a clear line of sight to the SCP and I'm currently relatively well aligned so I'll have a peek in the Polar scope see if I can see anything. :thumbsup: It's just the LP that is shocking. Sodium lights and what not from the industrial zone and the M7/M5 interchange... and people wonder why I do so much Ha. :lol:

[strongmanmike]

Do it next time you have drifted well at Wiruna, look in the polar scope and memorise (draw) the cross hair location in relation to the stars you can see, hopefully you will see it pointing close to where the charts Barry posted show it. When you get back home you may find it harder to see the right stars but at least you will be more familiar and have a better chance of recognising what you need.

Mike

[Barrykgerdes]

According to stellarium The south celestial pole will be almost exactly between the two numbered stars on my 100th birthday:thumbsup:

Yes that triangle apex was within an arc minute or so in 2000. I used it with my permanent mount. It got so easy to find in the end that I lined up the etx125 on my homemade wedge in the back yard.

If someone can paint the equatorial grid on the sky it will be even easier

Baz

[mithrandir]

It looks like 5' in Dec and 1 hr in RA. The orientation looks correct for around 14:30 today.

Andrew

[Octane]

In 45 minutes, I usually have one axis done via drifting. :whistles:

H

[Barrykgerdes]

yes the rings are 5 arc min spacing and I think the time was closer to 15:00 for the other screen shots I just scolled the time back to 2000

Baz

[gregbradley]

Nice writeup Mike and thanks to Barry for the position post that makes it
easier to follow.

I'll try that next time I am at my dark site. I guess you have to let your eyes adjust to the dark for a while. I find the polar scope very very dim even at a dark site. Perhaps I am too impatient.

Greg.

[Barrykgerdes]

If you want to get familiar with the view you can do it how I did it initially using the LX200 in alt/azm mode aligned accurately on two stars.

Just slew directly down to the south till you get to -90 (the GPS model will hit a software stop). Use your widest angle eyepiece to see the view. It is very recognizable.

Barry

[strongmanmike]

Is your NJP permanetly set up at your dark site? If so I guess it must be at least reasonably well aligned already so just look through the polar finder and you will see the two doubles in Barry's map easily and they should be near the centre of view. They may look singular though unless the seeing is excellent? You will be able to see Sigma in the FOV too somehwre near the outer 1/3 of the field, you need to place the cross hair on the Sigma Octans side of the two (double) stars, point the cross hair at the point indicated on Barry's 2011 map and you will deffinitely be within at least 2' of the pole but probably closer to 1' I'd say :thumbsup:

Mike

[avandonk]

If I was out in the wilds I would use this for a quick setup. You can attach it to a small monitor from Jcar that people use for reverse view in their car.

Not cheap but a lot easier for us old blokes than waiting for dark adaption and cricking your neck.

http://www.myastroshop.com.au/products/details.asp?id=MAS-071M2

Bert

[Barrykgerdes]

That camera idea is worth investigating (and investing in). Once correctly set on your polar axis (telescope) it should make centering quite easy. The polar scope on my G11 was salvaged from another mount (EQ3) and is pretty usless for Bert's reasons (and Polaris graticle). However I think I could build one using camera with a home made "telescope". I must look into it. It might be a worthwhile project.

Baz

[avandonk]

Barry all the EQ range have a north hemisphere graticule as well as south hemisphere. The image is from the GstarEx site and has a field of ten? degrees.

What I would do is accurately drift align the mount and then note the position of the SCP in the GstarEX or other video camera. You could also then align the polar scope very accurately.

When out in the dark sky sites setting up should be trivial.

Bert

[strongmanmike]

Excellent idea there Bert :thumbsup:...polar aligning ease for sure!

Mike

[Barrykgerdes]

Hi Bert

The polar scope I have only has a north graticle. It came out of a mount that only looked like an EQ3. I had hoped it was like the one in your picture but alas it is not. I adapted it to the G11 just to see if it could be adapted but using it as you say is a "pain in the neck"

Your method of alignment is the method I would use.

Barry

[coldlegs]

Does anyone have any long exposure pictures of the scp (at park) after accurately drift aligning? I would be interested to see the different field of views of the different scopes.
Stephen

[Barrykgerdes]

This can be synthesised very easily with stellarium.
Use the ocular plugin.

Set the telescope and eyepiece paramaters to suit your scope and eyepiece. (don't forget the X,Y settings if the image is on a newtonian.

To give calibration rings use the equatorial grid display.

Centre the display on the SCP .
Select the SCP and then ocular.

The display will show a view window of what the SCP will look like with that particular telescope set up.

If there are too many stars go to the main menu (F4) and reduce the absolute magnitude so only the brighter stars show.

By the way, the meade telescope at park will not park on the SCP. They will park at AZM 0 and Alt 0

The sample views are for an 80mm refractor, 500mm Focal length and 26mm plossl eyepiece (52deg FOV)

Barry

This particular configuration has a FOV of almost 3 degrees
Note that Sigma Octans is visible in the lower right. Time about 4:PM 17-5-2011

view as seen............. view with 1deg ring.............. view with star names

[mithrandir]

Barry is there any way to get Stellarium to display the SAO catalog numbers? It's a pain to convert HIP to SAO for use in my Gemini.

Andrew

[Barrykgerdes]

Not at the moment Andrew

One day we hope to have an assortment of star catalogues that can be used. I am sure there will be one somewhere that uses SAO numbers.

Barry

[coldlegs]

Barry
I'm talking about real images from something like an F10 scope looking through suburban light pollution. I did one last night which I think showed I was close but no prize.
Stephen

[Barrykgerdes]

It's a big at hard to know what you are pointing at with only two stars and no details of the focal length, camera or date/time but I doubt if that is anywhere closer to the SCP than 1 degree.

If that star is Sigma Octans the SCP would be in the direction you have indicated but about 50% further from the star than you have shown

Barry

[coldlegs]

Barry
The field of view is about 10 arc minutes, the scope is an F10 SCT with a toucam at prime.
Stephen

[Barrykgerdes]

Hi Stephen

If the FOV is only 10 arc minutes identifying the stars will be almost inpossible. You will need at least 30 arc mins FOV to get a recognizable view and that star in your picture is hardly likely to be Sigma Octans.

To calculate the FOV I need the focal length of the telescope F10 gives nothing about focal length just the ratio of the aperture to the focal length. I need one or the other to find the focal length.

With the tucam I need the chip size to calculate its FOV when coupled to the telescope. However at a guess I would expect from my experience the FOV would be about 1/4 of what I see using a 26 mm eyepiece and you would get about 9 arc minutes FOV if it was couple to an 8" SCT of the Meade or Celestron size.

Barry

[coldlegs]

Barry
The focal length is 2500mm and the chip size is 4.6mm X 3.97mm.
I'm fairly sure the field of view is somewhere around 9-11 arc minutes
but just wanted to verify the view from a real picture as well as stellarium.
I think there are two maybe three stars in the view..1-easy to see..2-dim...3 very furry and very dim but this maybe an effect of light pollution. Still it would be good to see someone else view of the scp, maybe from a dark location.
Stephen

[Paul Haese]

Legendary stuff Mike. With the EM400 I never got to use the polar scope because of the sky being blocked by the observatory walls and roof. I did note though that the view was a little hard to get right with lighting. Always have respect for anyone that can get polar scopes to work.:thumbsup:

[Barrykgerdes]

Hi Bert

I ordered from your description but that is only the bracket. The camera costs another $500 odd. However I have adapted a webcam ($40) to fit the bracket that might just be sensitive enough to work and is USB compatable.

I will test it sometime



Barry

[steve000]

I took this pic may 9 2010 from mums place, I have marked the near approximate location of the SCP

I often find it easier to locate things on an actual image rather than a star map.

the red dot inside the circle

[Barrykgerdes]

That's pretty close. You are about 3 or 4 arc mins out. The pole is, reference to your picture about 3 or 4 pixels up and to the left.

Look at the star just above your marker. Move about 1/4 of that distance up and to the left.

Barry

[Barrykgerdes]

Here is Polar Scope Mk2.
I re-boxed the Web cam and made a new mounting bracket.

[RobF]

Another way of doing this of course is turn on the crosshairs in your camera software and use the finder or main scope cameras.

I've always worried my scope mounting wasn't totally orthogonal with the mount, so recently I drift aligned my heart out in alt and az then tweaked the mounting assembly best I could to get close to the SCP.

Anyway, I've also attached some guider (SSAG) and CCD (QHY9) pics respectively for those interested. My FOV for the finder is about 2.5 degrees and the CCD about 1 degree. Hope these are of some use. Obviously you have to make sure your finder is very well centred on the CCD field (I used a bright star to do this). My finder in normally at PA180 (upside down versus the CCD when that is set up for N/S East/W i.e. PA 0 degrees).

p.s. I didn't say I was perfectly aligned here either for you perfectionists, but Maxim hardly even nudges my dec with this sort of alignment, so its not too far off. ;)

Actually I'm getting the best Polar alignment I've even had by pigging-backing some home made VB.NET off Maxim that monitors the average subpixel drift with tracking turned off and converts it to an arcmins value. I find with just 20-30secs of drift data I can get a pretty good indication or where I am for iterative adjustments. The monitoring time is left to increase of course the closer I get to the pole. Program also converts arcmins into "standard skywatcher azimuth knob turns" which is now an internationally metrologically sound unit for expressing PA error at my house......:whistle: :lol:

[Astroman]

I will most likely try mod the webcam idea also, I thought about doing this from this youtube video http://www.youtube.com/user/astronomyshed#p/u/24/5L6IvfievRE

I will most likely drift align to get it closer to perfect though.

[netwolf]

I tried using my friends polarscope on his G-11 once and found it a royal pain to do. But I must admit, that with some paitence i am sure it can be done. Hats of to you Mike and all those that use there polar scope, it would take a lot of paitence to do. Especially in surburban skies.

I saw that bracket on myastroshop and wondered if it would with the Qhy5 guide camera. The Qhy is quiet sensative and you could use PHDguider to do a few seconds exposure to see whats there. Just wonder if a Qhy5 will fit intot this bracket and weather it will work with a G-11.

BTW has anyone used any alternative Polar scope succesfully in a G-11? Is the Losmandy one the only option that will fit the G-11 or is there another option out there.

[Barrykgerdes]

Hi Fahim

That bracket could be made to fit most small CCD's with suitable lens and some attachments. but it would probably need some workshop facilities. I fitted the polar scope out of a eq3 mount to the G11. It went straight in. However it was an early version and did not have the southern hemisphere stars.

Whether the bracket will fit a G11 is something I can't check as Trevor has commandeered the G11.

The polar scope has about a 6 degree FOV so sigma octans should be located fairly easily with a bit of practice depending on the sensitivity of the CCD. However I doubt whether you could get closer than about 10 arcminutes with any consistancy and so final alignment would need a drift alignmnent.

Barry