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Your 2 cents Martin is great info. It gives me more confidence in the F ratios I'm using for considering a GSO mirror.
Now having come back from further star testing. I seems that my primary has settled down a little. I have elongated donuts inside and outside focus now but still in perpendicular directions.
I moved the mirror twice, 40deg and further to 60deg and the "pie section triangle" stars I found, pretty much stayed in the same orientation on all the frames. It was a bit hard to determine because my focus point is vague. A Batinov mask on a small star that gets best focus makes large stars deform out of focus, and vice versa. Also simply rotating the batinov mask on any star also causes big changes in the focus point. Too much going on at once......Very interesting to interpret the data.
I'm thinking, surely all this astigmatic spot and out of focus donut behaviour cant just be the secondary....Can it? Has anyone seen this sort of thing before with a secondary?
Or is it most likely that both mirrors contribute to the mayhem?
cheers
Dan
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