Imaging on grass

Tom Blahovici

Being in Canada, last night would have been a good night to take this literally....However...
Last night I tried out my portable "wheely bar" setup for my FSQ106 and AP600 GTO mount.  I used 1 foot by 1 foot, 2 inch thick concrete blocks under the leveling screws and did a polar alignment with the polar scope in the AP600.
My first image, 30 minutes O3 on NGC7000 was amazing.  The tracking, was 0.25" with pretty well no corrections at all. Granted the seeing was really special last night, very rare.
My imaging uses Voyager and I typically focus each 30 minutes where the scope does a goto to a nearby star in the Voyager database and then continues imaging.
After the first image I started to get large gradual swings in the dec and RA, up to 4" of arc errors after which Voyager would abort and start over. After two or so tries I then managed to get another nice sub.  Likewise for the third sub.  After this, I was no longer really successful.
So I took a look at the polar alignment through the polar scope and polaris had moved quite a lot. Probably a good 1/8 to 1/4 of the field of view.
So my thinking is that as the night progressed, and the scope changed position, the blocks started to shift.  This happened during the exposures.
So, how do you image on grass?  Is 30 minute subs out of the question?  Do you polar align frequently?
Thanks for any insight.

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