Optical Interferometry?

[chiltonstar]

Big aperture performance (resolution) from small refractors.

I'm sure that someone will know the answer to this one: if you combine the light from two small, identical refractors placed say 1 metre apart, will the resolution of the combination not be equivalent to a scope of 1 metre aperture (obviously the light grasp won't) if you look at the difference signal from a ccd placed at the focus of each? Alternatively, split the light coming into the small scope with a right angle prism and two front-surface mirrors.

Chris:icon_scratch:

[lunator]

Hi Chilton I'm no expert but I beleive this is the case.

The issue you have is that the atmosphere will limit the resolution so you would need a method to overcome this.

Also the light grasp may limit the objects you can go for.

Cheers

Ian

[Ben Ritchie]

In theory, yes, in practice, it's really rather difficult.

[FraserClarke]

if you look at the difference signal from a ccd placed at the focus of each?

No. You need to combine the light before you detect it; so you need to bring the light from the two telescopes together, overlap it, and detect the resulting interference pattern (to be technical, you destroy all the phase information when you detect the photon, so you need to interfere before you detect). You would get the resolution of a 1m telescope only in one direction. In the other direction you still have the resolution of the single telescopes. So you end up with elongated stripes, rather than a round star with airy rings.

You can do an experiment on a larger telescope (say 12") to show the effect; Make a cardboard cover for the mirror, and cut out two small holes (2--3") on either side of the cover. Then look at a bright star with the cover on. You'll see the airy disc of the star, crossed by series of black lines. The size airy disk is the resolution of the holes, the spacing of the black lines is the resolution of the separation of the holes. Nice bit of eyepiece interferometry The lines will come and go as the atmosphere changes the phase between the two holes; but your eye can track it.

I think I posted a video of this somewhere on here...

Edit: Here;

http://stargazerslounge.com/equipment-discussion/79689-how-do-you-build-optical-array-telescope-2.html#post1390899

[ollypenrice]

Isn't the real problem the unhelpfully short wavelength of light as compared with the more tolerant wavelngth of radio emission in which interferometry works wonders?

Olly

[chiltonstar]

Many thanks for these replies.

Shame, looks as though I will have to build a light bucket after all and move somewhere with more clear nights per year than the UK to make it worthwhile!

;)Chris