Re: Imaging on grass

Don Anderson

Hi Tom I'm in Calgary and image on grass as well with my AP900GOTO and a Televue NP127is on an AP portable pier. I tried cement blocks as well but found they move too much as the weight of my rig compresses the grass under the blocks. I have since gone to  three steel plates with two 8" pieces of rebar rod welded to the bottom of each plate. I pound these into the ground and leave them there. As the grass dies under them, they sink down to the dirt and are reasonably, but not totally, stable. I minimize movement by setting up my rig several hours before imaging which gives the plates a chance to settle in a stable position. This works ok since I image at between 525 and 660mm f/l. This wouldn't be very satisfactory at longer f/l. My next thought is to set up a permanent pier to which I would install my rig every time I image or drill three 6" holes 4' deep and pour concrete pads level with the ground. 
Hope this helps.
Attached is a pic of my setup.

Don Anderson

On Sunday, July 11, 2021, 11:01:26 a.m. MDT, Tom Blahovici <tom.va2fsq@...> 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.

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