Re: Building 30" Drum Scope

On Sat, 30 May 2009 16:38:58 -0700 (PDT), Hayden
<haydenfleming@xxxxxxxxx> wrote:

You said there is no airy pattern for any case other than a single
incident plane wave. Well. When viewing double stars with
a telescope with objective, one can see two airy patterns
separately representing the two stars, isn't it.

That is approximately true. In reality, no matter how far apart the two
star images are, however, their interference patterns overlap, and the
resulting field isn't an Airy pattern.

In a telescope without objective (just the hole), the pattern
of the 2 stars kinda merge into one interference pattern?

2 stars is the easiest illustration. So in aperture without objective,
they form one blob of interference patterns for both stars.
Now insert an objective.

When you are simply looking at point sources, the only effect of the
objective is to bring the far field zone close to the objective (there
is a magnification factor as well, but it is irrelevant to this
discussion). In other words, it lets you see the Fraunhofer diffraction
pattern without having your screen very far from the aperture, as would
be the case without the objective. Other than scale, the pattern is the
same in either case (and is called an Airy pattern in the case of a
single point source).
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.

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