Polar Aligning

[sheeny]

Hi guys,

After a break of about 20 years I'm getting back into astronomy again, and I have to say notice a few things have changed! ...mainly goto scopes and CCD cameras!

With my old manual scope (home made 8" f6 newt on a samson eq mount) I used to polar align by setting the declination of a star close to the horizon and adjust the mount in azimuth to align. It was simple, quick and acurate enough for casual observing.

These days I have new (fandangled) scope and I'm starting to play about with piggy back photography (with a view to progressing to other methods as I develop).

My question is, what methods do other people use to polar align accurately enough for photography on a portable scope? Do you simply find and align on sigma octantis, or do you get more sophisticated than that (I know you would for prime focus deep sky stuff)?

Primarily I'm just interested in eliminating field rotation in piggy back wide field shots, but eventually I'll need to get more accurate.

Thanks in advance,

Al.;)

[beren]

Gday Al ...welcome back....i go through the dift aligning procedure , was a chore at first but its straight forward now that when i have the scope set up for imaging i always do it . I have never tested how a relatively rough polar alignment affects piggyback shots with different lens , i think to at different points in the sky you get bizzare feild rotation rates so i think to avoid frustration getting your dift alignment to a point where a star doesnt move off a reticle line for 5 minutes will yeild good results for you.Good luck with the endevour and update your progress here to and welcome again.

[Robby]

If your mount has a polar scope then aligning that on SigmaOctans will be fine for piggyback. Failing that the drigt alignement technique that you already seem to know how to do is the way to go.
Here's a very detailed site on drift alignement. You can skip all the technical rubbish and go striaight to the instructions!
http://members.aol.com/ccdastro/drift-align.htm
Cheers

[johnno]

Hi all,
Just reading this thread,and noticed the link to Polar Alignment.
Very good info,Thanks Robby
Regards.John

[seeker372011]

who can see Sigma Octans ? Maybe once every three months.
there oughter be a law

[acropolite]

I'm with you Seeker, I've never even been able to find it; am I right in assuming that once I mount my wedge it will be an easier task as at least I'll have a field of reference once my setup is pointed roughly south and 42 degrees up. :confuse2:

[sheeny]

Thanks, guys. The drift technique sounds like the go. I have been lazy since getting my new scope... a rough alignment by compass/eye, and the goto system does the rest - fine for observation by eye, but not good enough for photography.

I was out last night, and I think my site is pretty dark (22ks from the nearest street lights) but I have to admit I had some difficulty seeing and identifying sigma octantis! Part of that is my lack of familiarity with Octans, and partly because they are just dim stars (I won't mention my eyes if you don't)...

So, question for you Goto scope users... if I do a rough align by compass/eye say, then autoalign, then check and correct drift, should I do a full auto align again after messing with the lat/az? I assume I should, but I'm not entirely clear on what maths the goto actually does.

Thanks,

Al.

[beren]

http://www.users.bigpond.com/lansma/art_sh_polar_alignment.htm this may help

[mch62]

Octans can be a challenge to find if you have never seen them before or live in the city as there only 5-6th mag stars.
I did find them in Strikers EQ6 polar scope when I set it up and he's right bang in the middle of Brisbane and can't see the Magellan clouds or most of the milky way.
Once you have used them a few times it becomes easier to locate them , but I wouldn't want to do it in Brisbane again.
You need to use a compass first and know the deviation for you area ( look on the web) and adjust the RA axis to point to that deviation position for true south.
Magnetic south from a compass is not true south.
Then you will need to set the altitude of the RA to your latitude. Best done using an adjustable bubble level on the tube as some latitude scales on scope mounts are not very accurate or the scale was not put on with care.
mine was out by 4degs.
Also the same can be said about the polar scopes.
My EQ6 polar scope was initially out by the width of the four main Octans stars.
It is able to be collimated like a finder scope , but be aware of the Chinese polar scopes and check them with a drift alignment .
If you can get these steps pretty accurate they will usually be in the field of view and just a matter of rotating the polar scope to the correct orintation.
Even if drift aligning these initial steps done accuratly will shorten the driftprocedure.

This is good enough for short wide field imaging or planetary imaging and visual use but then you need to fine tune it with a drift alignment for longer exposures and higher power imaging.
.
This can be done the old fashion tedious way with an illuminated eyepiece or better still get a copy of K3CCD tools and use the polar alignment tool included .
You will require some form of CCD camera like a cheap web cam (ToUcam)
This later method is so much quicker and easier and less frustrating.
With practice either way you will get it down to sub 15minutes or the later 5.

Mark

[Thiink]

Hey, another central west person! Welcome sheeny. :)