[PRejto (Peter)]

I could use some help in figuring out my results to date experimenting with an SX-AO on telescope #2 of my dual scope setup.

The largest unresolved issue I face with my system is that of differential flexure between the two scopes. I can fairly reliably go 5 min on scope #2 whilst guiding scope 1 through an ONAG. Sometimes I can go 10 min but too many subs show substantial movement in that time period depending on scope orientation.

After thinking about the issue for a long time (and after a suggestion by another IIS member) I decided to try to eliminate DF on scope #2 by using AO on scope 2 (but without any mount corrections). So, scope 1 would guide and scope #2 would have the benefit of AO corrections. Yikes, easier said than done!

My first experiments were total and complete failures no matter what combination of guide settings in TSX (scope 1) or AO settings (scope 2). The results were always a very poor image and one much worse than not using the AO. But, I know the AO is working great and properly calibrated as it will guide scope #2 perfectly if guiding is turned off in scope #1.


Thus began the trouble shooting. I decided to guide scope #1 and just watch what scope #2 shows when tracking a star (but applying no AO or other corrections). The result is uniformly the same regardless of the scope orientation unlike what I might expect to see from DF (where DF ought to be different in different sky locations, etc). Attached is a screen capture of 6 min of "watching" scope #2 in PHD2. The drift is ca -1 pix in 6 min and always in the same direction. This is an ST-i through my TEC140 = 1.56 arc-sec.


EDIT: Just to be perfectly clear I'm seeing this constant drift while I am guiding in TSX. There is zero drift in TSX with great guiding. The drift is just showing up in scope #2.

So, the question is what is this if it isn't DF? Am I just measuring field rotation because I have selected 2 different guide stars between the two guide cameras? I've yet to positively try guiding on the same star. Last night I was fairly sure both stars were quite close together but I still saw the same amount of drift. Tonight I will plate solve both guiders and try again. I think if I get no drift using the same guide star the idea of field rotation will be confirmed. And, if so, it's no wonder my intial tests using the AO failed.

Any other ideas?

Thanks for reading!

Peter