Quote:
Originally Posted by multiweb
Oh wow. Is the whole telescope design a Ritchey Chrétien or other? Must be a manufacturing nightmare. How do they independantly test segments that have those "exotic" asymetric shapes I imagine yet focus each area of light to the same point? Do they use some kind of scafold in the factory with the elements in their respective position from the optical axis for figuring and testing?
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Hi Marc,
It is an RC design.
As I understand it, to fabricate a segment, the clever part was to polish
a blank as a sphere whilst applying specific differing forces around the
edge of the glass. Apparently polishing a sphere is relatively easy
(Mark Suching was here a short while ago and I could have asked him).
When they then released the forces the glass which had been under stress
magically popped into the right shape and was then ready for final figuring.
When they built the AAT back in the 70's it was the first large digital
computer controlled telescope. We take computer control of telescopes
for granted now but at the time the AAT was built it was regarded as a risky
decision. However in the case of the AAT the computer is just performing
the task of pointing and tracking.
With the Kecks, not only is the mount itself computer controlled but
the optics are computer controlled. In order to maintain its figure,
sensors can measure multiple positions on each segment with micron
precision and actuators then in realtime change its position or shape
to compensate as the primary shifts its position as a function of gravity.
It's funny thinking of the actual optics of your telescope being
computer controlled but without it the Kecks would not be able to
achieve their incredible optical performance. These are the telescopes
that first detected extrasolar planets.
One other notable characteristic of the Kecks is their ability to image
into the infrared. The optics, instrumentation and siting so high
up in the dry atmosphere were all designed to achieve this. So a lot
of their observations are done at infrared wavelengths which is precisely
what you want for deeply red-shifted targets.