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Old 30-12-2013, 11:46 AM
mbaddah (Mohammed)
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mbaddah is offline
 
Join Date: Aug 2007
Location: Sydney
Posts: 803
Help with drift aligning an Astrotrac please...

I'm still struggling to get a decent polar alignment happening with my Astrotrac at 100-200mm I can manage to get a 1-2 of minutes with focal lengths of 70mm and below, but the moment i exceed that focal length I'm tearing my hair out in frustration trying to figure out what I'm doing wrong.

My drift alignment process is as follows:

1. Set up Benro A257 tripod
2. Attach Manfrotto 410 Jr geared head
3. Attach Astrotrac on top of Manfrotto 410 and turn Astrotrac to the right for Southern Hemisphere orientation.
4. Attach Manfrotto 488rc2 ball head on top of the Astrotrac
5. Attach camera and lens to ballhead
6. Set compass N dial 12 deg to the E.
7. Rotate AZ wedge dial until N/S aligned
8. Attach inclinometer and adjust altitude dial until astrotrac is at 34 deg
9. Take a test shot with the 70-200mm lens attached at 200mm aimed at the celestial equator and meridian (0 dec) for 30 seconds.
10. Adjust az knob towards East (or West) direction, take another test shot. If drift reduced, turn slightly in same direction and take another test shot.
11. Repeat until drift completely eliminated using 1-2 minute subs.
12. Point camera to the West, at star ~20deg above horizon and 0deg declination.
13. Take a 30second test shot. Usually there is a large amount of drift here.
14. Adjust altitude knob slightly in one direction (North or South) and re-take test shot.
15. If drift reduced proceed to turn knob in same direction while taking test shots until drift is eliminated. This is a bit of hit and miss here as sometime i’m able to completely eliminate it and other times there’s a slight drift which i can’t seem to get rid of.

Now at this point, if I re-point the camera to the North and take an image (in same direction i used to adjust azimuth), It’s like I never adjusted it and the initial drift returns. If I drift align the Azimuth again, then I lose the alignment in the West direction and the drift returns there. I can't seem to maintain an alignment in one direction without it effecting the other?

I know there are astrotrac owners out there who are able to get 3-4minutes subs at 200mm unguided, which is in accordance with Astrotracs claim. I obviously must be doing something wrong ?

If anyone could assist it'd be greatly appreciated, thanks

Last edited by mbaddah; 30-12-2013 at 12:04 PM.
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