On 21 Sep, 00:36, HW@....(Henri Wilson) wrote:
On Wed, 19 Sep 2007 21:45:03 +0100, "George Dishman" wrote:
"Henri Wilson" HW@.... wrote in message ...

Garbage, you get one photon from a distant nebula
or whatever and it lands on the CCD at a point that
depends on the whole telescope. A second later you
get the next photon and it lands on a different
pixel because it came from a different part of the
nebula a few light years from the first photon.

Well you wont get a continuous wavefront or any interference then...You
just get a normal image...albeit very slowly..

That's what you might think but if you have
the two separated telescopes, you still get
interference. Henry, I'm just telling you
what happens in practice, it is up to you
to make sure your ideas can cope with that.

George, I don't think you have a clue.

Let's see ...

What do you think might be the focal length of a 100 metre aperture
telescop?..maybe 1000 metres??

MELIPAL and ANTU are 8.2m in diameter and have a focal
length of 14.35m.

Do you believe a some kind of mirror system is erected way up in the sky and
moved around with a tracking mechanism?

Of course not.

http://tinyurl.com/3dybf3

The position of the secondary mirror above the primary
and location of the Nasmyth and Coude focal planes are
shown in the diagram, why didn't you look instead of
making a fool of yourself.

The fact is the two separated telescopes don't move like a single mirror would.
Each is rotated on its own base and has its own 'eyepiece'. The two behave
somewhat like adjacent lines on a grating.

Exactly, which is why I told you that your ballistic
grating equation applies.

The incoming signals are then
analysed in terms of the phase difference between the two images.

Yes, the two paths are brought together so that the phase
difference creates an interference pattern as shown in
the ESO diagram.

What "common wavefront" are you talking about?

...that across a spherical surface normal to the LOS.

OK, that's what you get with each individual
photon.

So photons spread out as they travel... I can go along with that to some
extent....but there is still a problem with gammas...

Individual photons exhibit interference over the 102m
between the two telescopes. Gamma telescopes are smaller
but if they could be made to a comparable tolerance
(fraction of a wavelength) they would show the same
behaviour. If that gives a problem, it is your problem.

Otherwise, no deteiled image could be formed at all.

Each photon lands on a pixel that depends on the
source location and the PSF, nothing else. If it
was affected by the previous photon in some way
then photons coming from one part of the nebula
would be scattered over the CCD depending on where
the preceding photn was from, the image would be
blurred. You only get a sharp image because every
photon behaves completely independently of all
other photons and goes where it is supposed to.

Well I would be inclined to agree with that...and c+v doesn't cause any
blurring because no photons overtake other ones.

It wouldn't matter if they did, as long as they don't
alter the fact that the wavefront is normal to the
line of sight, you get an image.

....an image of events that occurred at different times.

"Each photon" Henry. Telescopes detect individual
photons.

However this doesn't back up your and Paul's claim that one photon can
extend
and remain coherent over a 600 m circle.

No, that is quite different. The evidence is that
combining the light from widely separated telescopes
produces interference patterns. What the imaging
argumnent requires is that you cannot combine multiple
photons into a single 'average' wavefront because each
must point independently back to its source or the
image would collapse to a point. Low arrival rates
also mean you can directly see interference in systems
where the detectors work in photon counting mode, just
as with PM tubes and gratings. All the evidence says
the same thing.

You're guessing George....see above....

It is obvious that, if you average the location of
the wavefronts of two photons, the normal points
back to a location half way between the two sources,
you could not form a sharp image with a telescope
which Paul has been pointing out for some time.

Photon counting mode is used regularly in astronomy
and long exposures to handle low photon arrival
rates are commonplace. I am telling you what happens,
writing the equations to explain it is your problem.

George