Re: Building 30" Drum Scope
- From: Hayden <haydenfleming@xxxxxxxxx>
- Date: Sat, 30 May 2009 01:41:22 -0700 (PDT)
On May 26, 8:32 am, Chris L Peterson <c...@xxxxxxxxxxxxxxxxxx> wrote:
On Mon, 25 May 2009 17:19:53 -0700 (PDT), Hayden
<haydenflem...@xxxxxxxxx> wrote:
Here's an astonishing fact, a telescope can still resolve
object at the aperture resolving limit even without any lens present
since it depends on the aperture size only. Now if
I get a water drum and remove the bottom, then I can
have a 30 inches aperture scope, but without any lens.
Anyone has any idea how else like electronics means
to focus the light at the focal point without using any lens?
It's simple. Without an objective, the focal plane is at infinity. Just
put your camera infinitely far from the drum aperture. Note that you are
going to need infinitely small pixels, since the FOV is infinitely
narrow.
I can't believe why you mention that without an objective,
the focal plane is at infinity. Unless you are mistaken?
Ever heard of Fraunhofer farfield beam divergence of
1.22 lambda/diameter when it has propagated a
distance greater than r^2/lambda (where r is radius
of pinhole) beyond the opening. You are supposed to
see the Fraunhofer far field patterns too forming
image. So how can you say focal plane is at infinity
for an aperture without any objective?
Hay
You would be advised to keep in mind that just because optical theory
lets you analyze a particular case doesn't mean it translates to
something practical.
_________________________________________________
Chris L Peterson
Cloudbait Observatoryhttp://www.cloudbait.com
.
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