Drift Alignment

[Exfso (Peter)]

Here is a handy program from Andy's shot glass, called star targ, it costs $19.00usd, it is brilliant, makes drift aligning a doddle.

http://www.andysshotglass.com/StarTarg.html
They have all sorts of tutorials on this site as well.

[CarlJoseph (Carl)]

Thanks for a great thread. Wish I had read it before last night.

After 2.5 hours trying this yesterday ... I gave up. It's starting to make sense, but I'm not quite there yet. Actually practicing though helped a few things to click ...

We pick two stars because their positions show off the drift/movement more noticeably:

• A star right above you (near the equator and meridian) = Azimuth - mount's position on the ground.
• A star in the lower east/west (still near the equator) = Latitude - mount's position up/down.

But I still had a big problem ... I could not for the life of me get the star to sit still. I could barely even get it to slow down. Oh and yes, I did have the drive running.

Is the intention to get the star to stop in the cross-hairs or just to have it not drift off the line? I could get it to stay right on the line but never dead still. It was like the stars moved faster than my EQ6 could keep up with.

Should the star movement become slower the closer you get and eventually reverse once you've gone too far?

Cheers,
Af.

[Chancellor (Jeff)]

Hi Carl
Yes, the star movement should get slower the closer you get to alignment, and eventually reverse direction if you have gone too far.

The aim is to get the star to sit on the crosshairs for as long as possible.

Also, make sure that you have set the tracking to sidereal rate as this could also be causing issues if you select the wrong one. (I only mention it because I was bitten by this once).

[Octane (Humayun)]

+1 for StarTarg. That is the reticle that I use.

Carl, when you're pointing the scope at a star at the meridian, you are correcting for drift in ONE direction, only. Your goal is to minimise/eliminate drift in just ONE direction. That is to say, that you will still have drift in the uncorrected axis. When you swing over to the eastern/western horizon, you are now correcting for drift in one direction, again.

The goal is to iterate several times until you get no drift in either axis.

A good way to tell if you're making the right adjustment is to time how long it takes for the star to move a known distance (if you don't have access to an on-screen reticle, then, open an application or bring something up on screen which you can use as a marker or a reference gauge).

Example:

Azimuth adjustment: time how long it takes for the star to move. If it takes, say, 30 seconds, to move 3 centimetres, make an adjustment in azimuth, one way or another -- it usually helps if the first adjustment is a relatively big adjustment rather than a small one -- it is a lot easier to perceive movement after big adjustments. Measure the drift again. If it now takes 60 seconds to move 3 centimetres, then, you know you've made the right adjustment. Keep making those adjustments until you can get around 5 minutes without any drift.

Now, point the scope to the horizon and do the same thing, except, this time you'll be making adjustments to your altitude. Once you can attain 5 minutes without movement, swing the scope back to the meridian, and check again. Unless your mount is 100% perfectly level (spirit levels lie!), when you make an adjustment in one axis, it affects the other axis, too. Hence the iterative process.

H

[CarlJoseph (Carl)]

Originally Posted by Chancellor

Also, make sure that you have set the tracking to sidereal rate as this could also be causing issues if you select the wrong one. (I only mention it because I was bitten by this once).

And I'm soooo glad you mentioned it because this was the biggest part of my problem the other night. Apparently the Synscan doesn't start tracking in sidereal until you have it slew to a star (or do a 1/2/3 star alignment). I set it manually when I switched it on last night and it made a huge difference.

Originally Posted by Octane

A good way to tell if you're making the right adjustment is to time how long it takes for the star to move a known distance

Such a simple concept but this helped me a lot too. I set it up on a known point on my screen, sat down and watched the skies for a few minutes, came back to the screen to check where things have moved.

Originally Posted by Octane

Once you can attain 5 minutes without movement, swing the scope back to the meridian, and check again. Unless your mount is 100% perfectly level (spirit levels lie!), when you make an adjustment in one axis, it affects the other axis, too. Hence the iterative process

Another great tip for me. I only worked for 2 minutes without movement (impatient I know! ) but it was good for my second real practice at it.

Cheers,
Af.

[Octane (Humayun)]

Carl,

Top stuff -- the important thing is that you've learned the concept. The next time you go out to do it, it'll be a no brainer.

I guess the important thing is that you begin by pointing roughly due south (I love my iPhone for this purpose; I use its inbuilt compass as well as an app called Declination which lets you know how far east/west off south you need to be to be pointing to true south) and have the mount reasonably level.

Happy to hear you've made progress.

H