Frank & Jon,
See Stachiw’s book…it discusses virtual images due to
domed ports and also how to redirect images with add on pieces of
acrylic. Remember that water and acrylic have about the same optical
density so normal lens calculations would not be used…only the lens side
in the air media would effect the travel of light.
This would be a lot of work for little gain.
R/Jay
Jay K. Jeffries
Andros Is., Bahamas
A skimmer afloat is but a submarine, so poorly built it will not
plunge…
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Sunday, August 26, 2007 12:58 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] viewports
I was pretty heavy into amateur
astronomy in my life prior to submersibles, so have some knowledge on
this. First, the port would act like a lens only if it were shaped like a
lens. A bit thicker in the middle would not necessarily make it a
lens. It would depend upon the amount of curve and the shape of the
curve. Lenses (good ones) are specific geometric shapes such as parabola,
hyperbola, etc. If these shapes are not within specific tolerances, you
get chromatic aberration, spherical aberration, and a buch of other nastyness
that makes looking through them worthless.
A plane disc viewport that was a
little thicker in the middle would not be described as a stronger port as far
as ASME PVHO is concerned. While the port does not have to be
scientifically flat (same thickness from edge to edge), you have to use the
thinnest thickness to calculate the depth rating of the port, since that is
it's weakest point.
If the shape was such that the
port acted as a lens, and assuming the shape was good enough that various
aberrations were not present, then yes you would have to be at the focal point
in order to see anything clearly. This is most likely not going to be a
comfortable viewing angle. It's not like the lens is going to project a
bigger image of the world into the interior of the sub. If the port were
16 inches in diameter for example, it might be like looking through an 8 inch
viewport. You will have to be some distance back, and your field of
vision will significantly decrease because of that. Unless the port is a
perfect lens, as you view things further at the edges, the distortion gets
worse.
The port would not bring more
light into the sub, it would simply focus it into a smaller area. That
smaller area would be brighter since the light rays woud be concentrated,
however you are sacrificing field of view for brightness.
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On
Behalf Of ShellyDalg@aol.com
Sent: Sunday, August 26, 2007 12:29 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] viewports
I was welding on my hatch
yesterday, and an idea came to me.
If a flat disc type view port was
shaped thicker in the middle, like a lens, would it act like a magnifying
glass?
What kind of distortion would be
created?
How severe would that distortion
be or would it be like a car side mirror where " objects are
not as near as they appear"?
Would the shape add any strength
to the plexi?
Would there be a "focal
point" where you had to be a certain distance from the inside surface to
minimize the distortion?
Would the shape bring more light
into the sub? ( like a magnifying glass )
Would the slight convex shape
help with passing water over the surface?
If you were using a camera or
flood light from the inside, what would that shape do to the image captured by
the camera, or the light shining out from the light?
I might try a little experiment
if I can find a lens that I had laying around somewhere.
There is a dome viewport in the
Monterey Bay Aquarium but the distortion is pretty severe unless you have your
head right inside it ( about 36 inch diameter )
I didn't take the orange sub for
a ride at the convention, and I wonder what it looks like when you're in it and
submerged. With your head inside the dome hatch, is the view distorted? The
dome is mostly uniform in thickness, so I'm guessing it doesn't add much
distortion.
Anybody have any thoughts on
this? Frank D.
|