SL3telescopes

[T3D Peter Abrahams <telscope@xxxxxxxxxx>]

(thread abruptly yanked from its warm fuzzy photo home & thrust under the
inquisitorial glare of the technoids)

>With stereo, the brain can separate an object from the surrounding flack.
>Could that be any different than viewing an object through turbulence?

They certainly have a lot in common.  I hesitate to correlate the two
because the eye/brain flak is so many different noises:
--noise in the eye, floaters etc
--camouflage effects
--dust, glare, anything in the air that degrades images
But the air turbulence is a limited effect. The refractive index of the air
varies between cells of air, that measure 4 to 8 inches on the average.  A
larger aperture gets light from a bunch of these cells, and detail &
contrast are washed out.  An aperture about the size of a cell will have
moments of clarity, a larger scope will always have a cell or two in motion.
I believe that two small apertures would suffer from this same averaging.

>>...and two+ small holes show less turbulence than one hole of the same 
>>area

>How does this affect overall resolution?

When I said 2+ holes show less than one, I was either wrong or grieviously
mistaken.  Overall, reducing aperture reduces the visibility of turbulence,
and there is a critical point at somewhere around 4 to 8 inches.
A pair of one foot aperture scopes, placed 10 feet apart, can indeed mimic a
10 foot scope, and provide resolution that rivals the 10, but under severe
constraints, including precision in assembly on the order of a fraction of a
wavelength of light.  The Keck telescope has a twin, and they will be used
in this fashion, and there is a "Large Binocular Telescope"  being built,
with similar goals. (Two, 8.4 meter f1.14 mirrors on one mount, light
gathering power of one 11.8 meter mirror, resolving power of a 23 meter
mirror.  In Arizona.)
But to take a one foot scope & make a pair of two inch apertures out of it
would enhance resolution only if viewing conditions were horrible, and the
full aperture couldn't be used.  

>Can these several portions be added to advantage?

With telescopes, given decent optical quality, the limits to resolution are
mainly set by aperture.  Increasing aperture improves resolution
dramatically.  The influence of 'seeing conditions' is the complicating
factor, with turbulent conditions, a smaller aperture is often better. So,
yes they can be added, both to increase light grasp & contrast; and to mimic
a larger aperture & sort of attain its resolution.
As far as comparing a single small aperture to two small apertures, the pair
is at a disadvantage because of diffraction from the edge of the aperture,
the less edge per area, the better. 

>Can some sort of interferometry be used here? 

To 'stop down' a larger scope so you can get two beams to interfere has been
used, but again it is not so simple.  The Mt. Wilson 100 inch was used by
Michelson, but he put two smaller mirrors 20 feet apart and just used the
big one to bounce that light to an instrument, and he observed fringes, not
an image (of Betelgeuse).  There have been images built up from interference
observations, but that's more image processing or black magic than
photography (I believe).
Speckle interferometry is specifically designed to overcome atmospheric
turbulence, by using very short exposures, and it has been used with two
telescopes, but the light path to the instrument has to be exactly the same
length for each scope, to a fraction of a wavelength.  They did image the
surface of Betelgeuse this way, but again it was computer generated from
images of light patterns,

Binocular vision gives increased resolution over monocular vision, by
eliminating noise that is in only one eye.  3D gives more information, can
we call that resolution?   I don't see how twin apertures would give
increased res on telescopic objects, assuming:
--you can't see distant objects stereoscopically 
--you are comparing it with an aperture of the same area
--you aren't talking interferometry, which isn't imaging of the object, it's
imaging of the light, if I'm not mistaken.  

So, the mystery for me is: when viewing distant objects through twin
apertures is discussed, as an outgrowth of debate on SL3D, is it thought
that one can use SL3D techniques to extract z-axis information from distant
objects, and if so, how?
\\\\\\\\\\\\\\\\\\\\////////////////////
  Peter Abrahams    telscope@xxxxxxxxxx
the history of the telescope, the microscope,
   and the prism binocular


------------------------------