Re: [ATM] Any Amateur Adaptive or Active Optics ?

[Andy Saulietis <iss@pvtnetworks.net>]

Matt T writes,


>Are there any amateur active or adaptive optics in use , built or at least
>being developed ?

None that actually modify the wavefront to improve atmospheric
seeing. The SBIG 'AO' system is just a tip-tilt mirror that
moves the entire image  but doesn't reduce the size of the
optical image, just makes the moving average of the seeing disk smaller.

>The key ingredients seem to be already available in an almost suitable form
>, and the technologies involved are only getting cheaper, better and more
>widely available .
>There are flex mirrors, all they need now is maybe some electric actuators,
>there are amateur built ccd cameras, cheap webcams and digicams , all they
>need is a lenslet array to become a Shack Hartmann wavefront sensor. There
>are free programs to analyze Hartmann mask ccd images .
>There are very powerful and cheap computers , so why not amateur adaptive
>optics yet ?

That's the real problem, the wavefront sensor has to have a stellar source
outside the atmosphere to get the data needed to do the wavefront corrections,
this means either a big laser like on the Lick 36" that generates its
own reference image in the ionosphere, or a conveniently placed star
within the isoplanatic patch. This kind of laser system is *not* cheap.
See a recent S+T article on the subject.


>. I'm surprised nobody has put together anything yet that could be used or
>even built by amateurs .

Mel bartels et al have disussed passive systems that use thin mirrors
(~1") of 1-2m aperture that have actuators to control the figure of
the mirror using numerical models and measurements (like real-time Harmann 
testing) to maintain the
figure in the presence of variable loads like gravity, temperature gradients,
support flexure etc. The goal here is for amateurs to have access to larger
aperture instruments at low cost. Adding active wavefront control to this
is still, IMHO, too expensive and complex for amateur or commercial
telescopes. This is not to say its impossible, since a lot of the technology
required, especially computers and sensors, is currently available. What's
needed is to solve the wavefront measurement problem in an affordable way.





Andy Saulietis
ISS Enterprises
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