A Periscope for Viewing and Photographing Radioactive Objects Underwater Page: 6 of 12
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moved up and down over a distance of 32 inches by an elevating hand-
wheel which operates a lead screw through a gear reducer. As the view
tube moves vertically, its top end telescopes into an extension tube
that excludes light and dirt. A slotted bushing inside the bottom end
of the extension tube engages two longitudinal keys on the view tube
body. The extension tube, supported on a bushing that is mounted on
the operator's table at the floor level, may be rotated manually to
move the view tube through an angle of about 900 around its vertical
axis as a means of increasing the field of vision.
Four 150-watt spotlights are attached to brackets on the bottom
of the carriage, and are aimed at a spot about 20 inches in front of
the periscope window. Two of the lights are at the same elevation as
the window, and two are about 30 inches above. The lights are con-
trolled by switches that are mounted on the operator's table.
The underwater portion of the optical system consists of the glass
window that excludes "water from the periscope, and :a first-surface
mirror which is mounted at the intersection formed by the vertical view
tube and the short horizontal tube. The remainder of the optical
system, mounted on the table above the extension tube, is comprised of
a "Questar"* telescope and a 4" x 5" view camera which are coupled
together and aligned with the long axis of the view tube. It has a
three-inch aperture and is of the modified Schmidt-Cassegrain type;
the light path is reflected twice internally to give an effective focal
length of about four feet in a barrel eight inches long. Light that is
transmitted through the glass window is reflected from the mirror through
the view tube and into the telescope. On the control box of the tele-
scope are a side opening for the attachment of the viewing eyepiece and
an axial opening which is coupled with the camera. Light is directed
to one or the other of these openings by a star diagonal prism which
also serves as the camera shutter by excluding all light from the axial
opening when the prism is in position for viewing through the eyepiece.
The prism is moved by a lever on the control box. The periscope is
normally used to view objects that are placed about two feet in front
of the glass window, which makes the object-to-eyepiece distance about
twenty feet. At this viewing distance optical images of 2X, 4X, and 8X
object size can be obtained by means of interchangeable eyepieces and
an internal Barlow lens. If necessary, the telescope can be focused on
objects at distances of from eight feet to infinity. Photographic images
of 1X to about 10X can be obtained by extending the camera bellows;
however, because the limited amount of light that is usually available
* Product of the Questar Corp., New Hope, Pa.
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Locke, F. C. A Periscope for Viewing and Photographing Radioactive Objects Underwater, report, November 1, 1964; United States. (digital.library.unt.edu/ark:/67531/metadc1030032/m1/6/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.