Re: Imaging on grass


Dale Ghent
 

How bad this gets for any one person depends on ther soil type and moisture and all that. I use pavers sunk into the ground but major shifts aren't really anything noticeable with my clay soils. I'll start the evening guiding around 0.3" and it'll get to about 0.4 or 0.5". I'll touch up the PA every night, though. It's usually off by around 5-10" over the course of a day or two. I PA using sharpcap through my main camera.

On Jul 11, 2021, at 13:01, Tom Blahovici <tom.va2fsq@videotron.ca> wrote:

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.
Tom

<wheely.jpg>

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