Drift Alignment Problem

[rainwatcher (Peter)]

I carried out my first drift alignment exercise with my C8 on a standard wedge mount. In the drawing below are my results. I am concerned about an apparent EW drift that corrects itself. I have no idea what the periodic error of my C8 is but I would be surprised if it were as large as the diagram indicates. The diagrams are of the drift screen in BYE.
Explanation:
The top two are Altitude drifts using Alphard 09h28m13.127s -08°42'51.96" – about 9:30 pm. They are both 221 second drifts.
The first is my raw setup, the second is after I raised the altitude by adjusting the tripod leg. I repeated step 2 and got pretty much the same result. Since this was a test of my setup and procedure I did not attempt any further correction.
The lower diagram is of Azimuth, Cursa 05h08m28.651s -05°04'24.90" – about 10:00 pm. 230 second drift. I must have been good on the compass, but again the EW drift was large. The movement was uniform in that it went east to west and then west to east at the same rate.
I read that a slippy clutch can do it, but I retightened it before the second test and it felt pretty firm.
I am going to repeat the exercise tonight and run for at least 10 minutes, this time I will snapshot the screen, but in the meanwhile can anyone advise if they have had a similar problem and what steps I can take.

[Octane (Humayun)]

If you raise your tripod leg, you screw up the alignment in the opposing axis.

Refer to my posts here:

http://www.iceinspace.com.au/forum/s...ad.php?t=72389
http://www.iceinspace.com.au/forum/s...ad.php?t=73263

H

[rainwatcher (Peter)]

[QUOTE=Octane;813710]If you raise your tripod leg, you screw up the alignment in the opposing axis.

Hi, Octane, thanks for this response and I have read the posts you noted and yes it must be done in baby steps.

I accept that adjusting legs will normally screw up the other axis, however in my case the leg I adjusted is pointed True north, and the other two are aligned East-West. Now I understand that any slight deviation here will stuff up accurate polar alignment but in my case by adjusting the front leg I am only adjusting the latitude. I can not see why it would alter the EW alignment to the extent it would produce such an odd drift pattern as my azimuth attempt.

Please note I am not contradicting you , you are correct in your comments and I always read your posts with interest. I am just confused as to why it would drift East and then back at a uniform rate.

I will be trying again tonight. I must have kicked it or left the clutch loose . Maybe the camera I used (Canon 1000D) moved on its T mount, I actually found a little slop in the bayonet fitting when I checked it a minute ago.

This is not a permanent method for me as I will be installing a fine altitude adjuster to the wedge soon. I am just practicing my drift alignment skills using BYE and my Camera.

[Barrykgerdes]

When you do your drift alignment the parameter that is being tested is the dec drift (North south). The first step is to drift around the zenith adjusting only the east/west azimuth angle of your wedge. Ignore any cyclic E/W drift just make sure there is no N/S drift.

Next you do the same test with stars at the East and west horizon and adjust only the Altitude of your wedge. Once again ignore the cyclic E/W movement.

Repeat these steps til there is no drift anywhere in the N/S plane.

Now you can look at the E/W drift. If it is cyclic and returns to the same position every few minutes it will be PEC. If it does not return to exactly the same position there will be another problem as well as PEC. could be backlash, flexure, balance etc.

Barry

[alistairsam]

Hi,

I've been learning to drift align as well. can phd or guidemaster or any software be used to show you the drift of the guidestar in a graph when you're not guiding?

since the goal of the drift alignment process is to stop drift in the N/S direction or Dec, is guiding in Dec necessary as in theory, we've arrested that movement and only RA is bound to drift which the guiding will correct?

[[1ponders] (Paul)]

Peter do yourself a favour and download K3CCDTools (free for the first month or use the Ver 1 that is free but needs a new key each few months). Using its drift explorer you can measure your PE much more accurately. Its also fantastic for doing drift alignments. Just make sure you input your scope and camera details.

[adman (Adam)]

Originally Posted by alistairsam

can phd or guidemaster or any software be used to show you the drift of the guidestar in a graph when you're not guiding?

Yes. in the Brain button there is an option that says something like "Disable Guide Output" - so once you have calibrated, check that box, find a star and click the guide button then enable the graph. One trace will show your periodic error, and the other will show the DEC drift - if you are way out it drifts very quickly one way or the other. One line on the PHD graph equals one pixel, so you can use something like CCDCalc to calculate your periodic error etc.

Cheers'
Adam