Polar alignment for cluttered backyards

[RobF (Rob)]

Originally Posted by lazjen

Another solution is provided using Astrotortilla (plate solving software). It has a routine that takes using through PA using plate solving. You don't need to see the SCP for it - lowi(ish) east or west plus zenith to align the axes. Assuming you start out roughly close (using compass, say), it doesn't take too long to dial in the PA with it.

I'd be interested to hear more about this option Chris?

As an aside, it is fantastic how many PA solutions people have provided to the community, even in just the last 5 years! What a time to be an astro-nerd

[lazjen (Chris)]

Originally Posted by RobF

I'd be interested to hear more about this option Chris?

Here's a tutorial on setting up Astrotortilla (AT): http://www.lightvortexastronomy.com/...e-solving.html

I'll quote the manual as it describes the process:

4.3.2 Polar Alignment

Using a plate solver eliminates the waiting that’s distinctive in polar aligning your mount with the traditional drift method. Just solve a frame, turn the scope along RA and solve again. The difference in solved declination values is equal to the amount of drift in declination observed when tracking a star for a time equal to the amount turned.A tedious 20 minute drift can now be done in way less than a minute!

A pair of frames shot at the east/west meridian is used to determine the altitude error of the polar axis, and a pair shot at the southern meridian (assuming northern hemisphere observation) gets you the azimuthal error.

To use the tool, select Tools → Polar Alignment. Choose the correct hemisphere and point your mount roughly at the meridian to measure azimuth error or to the east or west to measure altitude error.

Then press the according button to let AstroTortilla shoot and solve the pair of frames. When done, your polar alignment error in degrees is shown on the screen. Use this to correct your alignment by turning the alignment knobs on your mount.

When measuring azimuthal error, be sure not to point within a half a degree or closer to the meridian to avoid meridian flips! Pointing on the west (right) side of the southern meridian is the safest bet.

I use AT with APT to acquire the images, but there are a few other choices available.

Since I can see SCP, I've switched to using SharpCap's PA routine and will be trying a new PA tool in PHD2 (not the drift align tool) sometime in the future. However I will fall back to this tool if I'm at a location where I can't use SCP.

[RobF (Rob)]

Thanks Chris - will have to try this.

[gregbradley]

I now use TPoint in the SkyX. It has an accurate polar alignment tool. I haven't found anything that can match it in accuracy. Its really accurate. But it takes about 30 minutes to do and you have to get plate solving to work (it can be fussy to setup but once done it should work every time).

Accurate polar alignment in TPoint will give you a PA that is more accurate than PemPro. Pempro I assume is more accurate than PHD2 (which only uses trend lines on autoguiding graph which Pempro also does but Pempro takes it further.

Accurate Polar Alignment also takes into consideration the fact that there is a refracted SCP.

You could probably get the time down to 15 minutes once you were familiar with it.

I doubt anything out there can match it. Its very refined. But you need Sky X and you need Tpoint.

Greg.

[Atmos (Colin)]

Originally Posted by gregbradley

You could probably get the time down to 15 minutes once you were familiar with it.

I doubt anything out there can match it. Its very refined. But you need Sky X and you need Tpoint.

+1

I got it down to 15 minutes with 16-25 point models. Also, as long as you know your pixel scale and get the exposure time right (2s 2x2 bin works brilliantly for me) it’s rsally easy.

The only package I’ve found that will rival it is the software package for the ASA mounts. It’s a little slower than T-Point mostly because TSX plate solves faster than PinPoint but it also doesn’t need as many points for accuracy. Still, TSX is blisteringly fast with its plate solving.

[04Stefan07 (Stefan)]

Originally Posted by peter_4059

+1 for PHD2 drift align.

Does the polar alignment need to be within a certain distance for this to work? I gave it a go last night but had no idea what was going on.

Think I need to re watch that tutorial I found online.

[kens (Ken)]

Originally Posted by 04Stefan07

Does the polar alignment need to be within a certain distance for this to work? I gave it a go last night but had no idea what was going on.

Think I need to re watch that tutorial I found online.

Its not essential but it helps. The hardest thing is to work out which way to adjust depending on the trendline. The next thing is how much to adjust. Once you work it out (e.g. left knob clockwise 1 turn = 5 arcmin or whatever you can write that in the notes for future reference.
If you are seeing big errors at first its worth making a big adjustment to work out which way to turn. Remember that when you are poiting t the hoizon you adjust altitude and when you are pointing at the meridian you adjust azimuth.

[xelasnave]

Originally Posted by kens

Its not essential but it helps. The hardest thing is to work out which way to adjust depending on the trendline. The next thing is how much to adjust. Once you work it out (e.g. left knob clockwise 1 turn = 5 arcmin or whatever you can write that in the notes for future reference.
If you are seeing big errors at first its worth making a big adjustment to work out which way to turn. Remember that when you are poiting t the hoizon you adjust altitude and when you are pointing at the meridian you adjust azimuth.

Now you tell me

I had this mixed up the very first time way back years ago.

I have been trying to get polar back since I moved the mount onto a pier and have started building the box ob around it all... but between much cloud...and a night or two ago having got it half reasonable after further adjustment completly stuffed it...

I hope its cloudy tonight so I dont have to bother with it...but if its clear I cant help myself..and that is crazy cause the mount will have to moved when I do the next stage of the ob box...

alex