RE: [PSUBS-MAILIST] viewports

Hi Frank,

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.

Jon

-----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.