Mirror Alignment: Keck Telescope Instrument Accuracy

[wolram]

I saw part of a documentary about the keck telescope, they used an instrument that vibrated if any thing came near it to align the mirror segments, this instrument has fantastic accuracy apparently, can anyone tell me what it is called please.

 

[Integral]

I am not 100% on this but try searching on "adaptive optics".

 

[mgb_phys]

The keck mirror uses lead screws with an encoder on the motor to position the segments.
There was a laser interferometer to set the initial positions (same one as the JCMT) then you use normal optical tests ( shack-hartman etc) to fine tune it.

For normal imaging operations the mirror only has to be aligned so all the elelments point in the correct direction - for interferometry you also have to have them all in phase, ie. the mirror-focus distance is the same fo rall elements.

There was some tests of a resonant inductive position sensor but it doesn't have any moving parts.

 

[wolram]

I am sorry i only saw part of the program, i think it was Richard Hammond demonstrating how this thing worked, it looked like a vertical rod connected to some electronics, as soon as he put his hand near it it produced a musical note.

 

[MrPickle]

The instrument measured the change in the electric field (not sure it was electric, but it was some sort of field :P) around it.

I saw that program too.

 

[mgb_phys]

Didn't see it but you could imagine a capacitance position sensor, don't know if the mirror coating would be thick enough to give you much of a signal but you could sense the support metalwork.

Shoudl work well on Keck, a big problem on Mauna Kea (and most astronomical sites) is that it's so dry you get huge static build-up. You kill a lot of hardware and learn to touch car doors with the key before your fingers!