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Old 06-08-2014, 09:26 PM
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Shiraz (Ray)
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Location: ardrossan south australia
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Quote:
Originally Posted by Peter Ward View Post
Interesting result.

I'd question whether all AO's are created equal.

The groundwork to SBIG's devices was done by Brad Wallis (Awarded a NASA prize his programming skills during the Cassini mission) and Benoit Shillings, ( BeOS creator and Software engineer with few equals). SBIG went through a very thorough evaluation process to determine what benefits an AO might offer, some time prior to offering it to the amateur market. ( I recall being asked to provide data for this early assessment some 15 years ago)

If the system hysteresis, acceleration and dampening is not well understood, modelled and controlled, it would not surprise me in the slightest to see tip/tilt systems making images worse.
(BTW AO acceleration and displacement is user/software adjustable with SBIG's systems)

But this has not been my experience using AO7, AO8, AOL and AOX units. I have always found stellar footprints were as small and intense with AO enabled as without. When the seeing has been good, I have constantly seen 30-50% improvements in both. As has been pointed out earlier, one need only look at Martin Pugh's recent AO data and compare that to his earlier, non-AO, images to see the benefits.
I rather think that you have completely missed the point Peter. The testing was done specifically to show that the concept of guiding on a star outside of the isokinetic patch can in some circumstances lead to negative results - AO's cannot be expected to "fix" sub-standard seeing because they suffer from this problem, although it is often claimed that they can. If I had used an SBIG AO I would expect the same result - unless they have somehow managed to bypass the physics of the atmosphere. As an SBIG distributor, you will naturally favour that product, but it seems a bit offside that you view this evaluation in terms of a shootout between competing AOs, when only one is being tested.

As was pointed out, if an AO is used under good seeing conditions, it should be able to fix residual mount/wind errors - I presume that is what Martin Pugh is finding, although I doubt that I will ever get seeing that is anything like good enough to confirm that idea.

Quote:
Originally Posted by Octane View Post
Would an AO unit be of any practical significance imaging at 530-850mm focal length?

H
Should be useful for correcting major mount errors (eg wind) in good seeing H. My testing was done at 800mm fl and the AO did what any AO would have done under the circumstances. The fl is immaterial (provided there is enough back focus) - what matters is the angular pixel scale, since the job of an AO is to modify the angles of the light rays. If you use small pixels at these focal lengths, AO should be advantageous under some circumstances - if you use big pixels and undersample, AO will be of less use.

Last edited by Shiraz; 07-08-2014 at 12:59 PM.
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