Accurate polar aligning.

[johnnyt123]

Hi Everyone.

I spent 3 hours last night trying to get near perfect polar alignment but failed miserably.

I have a HEQ5 pro goto mount
I tried to use the built in polar scope but could see absolutely nothing and I did have the declination axis turned at right angle to the N-S axis of the mount to allow light through the opening.
And it was worse when the mount was turned on. a red light within the polar scope tube virtually blinded me when looking through the eyepiece.

I then decided to use the scope i have mounted to align and after spending 30 min to pin point the south celestial pole, to my dismay when i rotated the mount about the RA axis neither that point nor the nearby Polaris Australis remained stationary.

So I gave up, tucked my tail between my legs and called it a night.

Does anyone here have good experience with polar alignment and can offer some recommendations/ help.

Would it be possible to meet up some night and observe how it is done properly? I live in Belmore, Sydney.

Any help or advice would be greatly appreciated.

Thanks

John

[Lee]

Do some searching, in here, and google, on 'drift alignment'.... it isn't hard once you get used to it.
I also think that tracking at the pole successfully is nigh on impossible.

A better test of your alignment is to centre a star near Dec 0, and watch if it drifts in the eyepiece.... (which is the premise underlying drift alignment too).

[RockHound]

If you use a laptop to connect to the mount and have a basic webcam/ccd camera try EQAlign

[Steffen]

Here's my procedure for quick setup and polar alignment with the HEQ5 Pro:


Upgrade the hand controller to firmware version 3.35.
Set down the tripod, use a compass to make the South leg (labelled "N") point south, compensate for the magnetic declination at the location.
If the ground is reasonably level don't bother with levelling the tripod.
Add the mount, counter-weights and scope. Adjust the mount elevation using the azimuth scale.
Turn on the mount, enter location, date, time and DST flag, be as careful and accurate as possible.
Perform a two-star alignment. After successful alignment the hand controller will display the polar alignment error in azimuth (Maz) and altitude (Mel).
If the azimuth error is larger than a couple of degrees yank the tripod around a bit. If the displayed Maz error is positive the South leg needs to be pulled to the West (right), if negative, to the East (left).
Likewise for altitude error, but the error is shown with the wrong sign (Southern hemisphere bug I presume). If the Mel error is positive the mount needs to point higher, if negative it needs to be adjusted lower.
Perform another two-star alignment to a) confirm that the adjustments have been in the right direction and b) that the mount is within a couple of degrees in alt and az. If not, repeat the previous three steps.
Use the Polar Alignment function in the Alignment menu. Refer to the SynScan 3.35 manual for details. Repeat until the polar alignment error is acceptable.
Do a final two-star alignment and start observing!


This works for me every time, and I get to sub-minute alignment errors within minutes after setting up the mount and scope. That's as far as I take it for my visual use. For imaging you can go nuts and repeat step 10 for as long as you like :)

Cheers
Steffen.

[alistairsam]

Drift alignment is the way to go if you're imaging.
I use the ccd drift alignment method which I find very accurate.
http://www.observatory.digital-sf.com/Polar_Alignment_CCDv1-1.pdf

A member here, Robin has written a cool program that automates it using Maxim and EQAscom.

If you're using the hand controller, you can adjust the brightness of the polar scope light with the hand controller settings.

These articles in the the projects section are good as well

http://www.iceinspace.com.au/63-405-0-0-1-0.html
http://www.iceinspace.com.au/63-466-0-0-1-0.html

you can try out the Drift Alignment simulator here
http://www.petesastrophotography.com/

Cheers
Alistair

[DJT]

Hi John

I used PHD's method for drift aligning after getting a rough alilgnment first. Its pretty quick and I got good results.

Also this link has been posted on some threads before and covers a number of methods

http://njstargazer.org/PolarAlignment.asp

I also practised using Petes Astrophotography simulator early on as drift alignment is tricksy first time out.

I live in Sydney and gave up on using the polar scope really early on as with the LP where I am I didnt have a hope.

Drift alignment (either manual or using software like EQalign or PHD or many others come to think of it is the way to go) is the way to go though by all accounts the synscan functionality in the handset for the mount once the software is updated should sort you out.

[Camknox]

I've got an iEQ45 and suffer the same problems with trying to get an acurate Poalr Alignment. I just can't make out what I'm meant to be seeing through the polar scope.

iOptron has roughly the same all star alignment as Celestron (apparently) but after an hour of back and forth iterations it just starts going wrong and I end up with the ALT set almost to the horizon from adjusting it as it tells me.

I've tried drift alignment but well that sucks worse.

[Camelopardalis]

I think I might be investing in an alt/az mount before long... polar aligning was so much easier in the northern hemisphere :D

[naskies]

Drift aligning definitely works, but I find it a bit time consuming and not intuitive if your initial polar alignment is extremely far out.

Software-based approaches use star pairs - you choose a pair of stars, slew to the first one, centre it, the software slews to where it thinks the second one should be, you correct any errors, and the software then "de-centres" the star by the amount that you have to adjust the polar alignment by. It's very, very quick even if your initial polar alignment is off by many degrees.

I personally use AlignMaster because it's what I started on, but popular alternatives include PolarAlignMax (based on plate solving) and the PA routine built into the latest firmware revisions of the SynScan handset.

For example, I can plonk my EQ6 down on the tripod and roughly eyeball south (phone compass during the day, or with the Southern Cross at night). The first star pair iteration might tell me that I'm off by 8 degrees in az, and 3 degrees in alt. I do the correction and repeat, and then I'm off by 30 arc min in az and alt. On the third iteration, I'm down to < 1 arc min PA error, which is fine for my imaging.

The most important thing with any technique, however, is to make sure that your tripod is horizontally level *and* whatever it's standing on is firm enough that it doesn't move while slewing. Tripod on soft grass/soil is a no no, in my experience. If the mount isn't level / moves, then you'll spend hours in frustration because every correction in one axis will mess up the other axis.

[Steffen]

I agree, soft or wobbly ground is a recipe for frustration. If all you have is a lawn then embedding three bricks or something may be a good idea.

I don't find levelling that important, though. The ground on my patio slopes by 2-3 degrees, this isn't a problem for polar alignment. Sure, alignment of the two axes will become dependent, but only by a small amount and the alignment will always converge quickly. I've never done more than three runs of the SynScan PA routine.

Unless it looks obviously crooked I wouldn't lose sleep over levelling the tripod.

Cheers
Steffen.

[Wavytone]

Steffen is right - levelling the mount doesn't really matter since we're on a spherical earth - any tilt is analogous to being at some other location on earth.

However it is helpful in a practical sense - especially if you want to be able to repeatedly set up an equatorial in the backyard using a reference point for azimuth and an inclinometer (to get the altitude of the polar axis set correctly).
If you have some bricks or concrete pads set in grass, and record which tripod leg goes where, the setup should be reasonably repeatable which will save you a lot of fiddling each time.

For alt-az mounts with encoders or GoTo, especially dobs, levelling also matters as it helps if the flexing of the mount is consistent in all azimuth directions.

[johnnyt123]

wow

thank you everyone for your rapid assistance.

Looks like drift aligning is the way to go.

Well i just updates my Synscan version from 3.32 to 3.35.
and am going to be practising drift aligning hopefully tonight.

Just want to ask if in order to verify drift aligning has been successful, can you ask the scope to goto the SCP and rotate the scope about the RA axis and see whether the SCP moves anywhere?
I really want this to be as accurate as possible as i want to spray paint where the tripod legs will be to save me setup time in the future.....

[Lee]

In a perfect world, with a perfect mount, yes - unlikely though, due to cone error etc etc.

Have a look into plate solving - this lets you accurately, to within arc seconds of determining where you are pointing. Slew to Dec 0 somewhere, solve the co-ords, then slew a couple of hours in RA only, if you are perfectly polar aligned, the new location's Dec should still be zero, polar misalignment will show as Dec drift....

[Steffen]

Not sure about that, the SCP isn't something you can see. If there are visible stars in the field then those should simply rotate around the centre, without shifting in any other direction.

That said, after polar alignment you'd have to do another two-star alignment of the mount anyway, and that will tell you your polar alignment error.

Cheers
Steffen.

[tlgerdes]

Johnny, one thing you didn't say was why you were polar aligning, is it for visual or photographic?

[johnnyt123]

I wanted to polar align for astrophotography.

I wanted it to be as perfect as possible so I could mark the position of the tripod's legs so that setting it up next time wouldn't take too long.

[tlgerdes]

Drift aligning then is the easiest and most reliable. I put together a Powerpoint presentation explaining it here ftp://www.sarcasmogerdes.com/download/Drift-alignment-using-PHD-graphs.pptx

You will of course need a guidescope and autoguider ;)

I field setup each month when I go to ASNSW Wiruna. I can be drift aligned in about 20mins using PHD's graphs. I don't have a permanent mount, I have 3 stone pavers I have embedded into the ground up there that I place my tripod on. This give me a rough south pointing position, then I set my altitude scale to about 32.5deg and start my alignment routine. Usually takes about 4-5 adjustments (about 1-2mins apart) in each direction (alt-az) to get me on the mark.

[johnnyt123]

Trevor,

That is an excellent guide to drift align with PHD

Thanks for that.

[tlgerdes]

Yeah, none of this, if the star drifts this way in the next 10 mins, then turn yourself to the left and hop up and down on one foot. :lol:

[Camknox]

This looks extremely cool! I'm heading away this weekend so I fully intend to try this as nothing else I am doing appears to work. Here's hoping for insane 5 minute guides!

[gregbradley]

Not sure if you are using a camera but if so you can use Star Targ which is an overlay with instructions for your computer screen. You use the camera to do the drift aligning. Its easy and fast plus it has instructions built in.

Polar alignment can be a source of frustration so whichever method you adopt plan on being expert at it as its the basis of future imaging and without it as a skill good images will not be possible. So its worth spending some serious time mastering it.

Greg.

[johnnyt123]

Greg do you have a link to download Stat Targ from?

[Tandum]

Don't waste your time with startarg, if you have a guide camera, just use PHD.

Get set up with a compass and level, and turn the scope east (90 degrees to the mount). Start PHD, connect to the guide camera and the scope if you pulse guide and start capturing (1 sec exp). Raise the scope slowly on RA to about 20 degrees or until you see a star in PHD. Lock that star and press the phd button to get it to calibrate. Let it calibrate.

Once it calibrates, press stop, now press the brain button and disable guiding output, it's a tick box. Start capture again, click that star again, click tools / enable graph on the overhead menus. Move the graph as you see fit and then click PHD again for guiding.

Watch DEC on the graph, ignore RA, not important. If it starts to go up or down, adjust altitude to shoot the line in the opposite direction in which it's moving. Stop and repeat. Eventually the line will start going the other way, you have turned it too far. Get it close then :-

Move RA, not DEC, and point scope straight up. It should be pointing a little north and more or less straight up. No need to calibrate again but do the same as before, find a star, clear the graph, start guiding. Now if the DEC starts going down turn left/right knobs to make it go the same way faster, off the screen. Reacquire a star and repeat. It will eventually go the opposite way so you have gone too far there.

Repeat step one and two if you want otherwise close enough.