Nonlinear Projections - Transformations and Projections in Computer Graphics - page 185

The Noblex [Noblex 05] is a family of cameras that consists of models 135, 150, and
175. Model 135 takes a 136 ◦ -wide image and uses standard 35-mm film. The Noblex-
150 provides a 146 ◦ angle of view, uses 120 film, and produces six 5-inch-wide images
on a roll. It can take multiple exposures on the same film.
A panoramic lens system (Figure 4.38c) is somewhat similar to a reflecting tele-
scope. Its main part is a convex parabolic mirror (in contrast to the mirrors used in
telescopes, which are concave) that captures the entire (or almost the entire) half-sphere
of image above it and sends it up, where it is reflected by a small, flat mirror and sent
down through a hole in the main mirror to a camera. There are no moving parts, no
rotating parts, no need for multiple images, and no need to stitch multiple photos to-
gether. The price for all this (aside from the price of the camera and mirror) is image
distortion. This lens can, in principle, be used with any camera, digital or film.
Since the mirror captures everything above it and on all sides, the only way for the
photographer to stay out of the picture is to crawl under the camera. A panoramic lens
system is therefore used while mounted on a tripod or a pole and operated from below.
AnexampleofthistypeisthePortalS1panoramiclenssystemmadebytheBeHere
company [BeHere 05]. It is 12.5 inches in diameter, 13 inches tall, and weighs less than
10 pounds. It has a 35-mm Nikon mount, so any Nikon-compatible camera body, digital
or film, can be used with the Portal S1. The depth of field of the Portal is from one
inch to infinity. (There is no need to focus the camera.) Its lateral field of view is, of
course, 360 ◦ , but its vertical field of view is limited to the gray area in the figure and
equals 100 ◦ (the angle between the two lines marked L ). When anything outside this
area is reflected in the main mirror, it cannot reach the secondary mirror.
If a film camera is used, the film can later be scanned and then processed with
special software provided by the manufacturer. This software flattens the donut-shaped
image and can also perform other processing such as evening out the lighting, correcting
brightness and contrast, and slightly sharpening the edges. The image can then be saved
in one of the popular panoramic formats such as QuickTime VR.
Exercise 4.13: Explain why the image produced by a panoramic lens system is shaped
like a donut.
The OmniAlert panoramic video camera system from Remotereality [remotereal-
ity 05] also employs a parabolic mirror, but the mirror points down, toward the camera,
which results in a circular picture with no hole. This camera has been developed for se-
curity and surveillance applications, where a wide field of view is important. The video
camera is mounted on a high pole right under the parabolic mirror and uses special
software to detect and track moving objects in its field of view and alert operators to
any suspicious activities.
The 360 One VR parabolic mirror system, from Kaidan [Kaidan 05], also uses a
down-pointing mirror and can be attached to several different cameras. Special software
must be used to convert the highly distorted image to a flat panorama (Flash VR,
cylindrical, QuickTime VR cylindrical, spherical, cubic, or QuickTime VR cubic) that
can be displayed and printed.
See also [eclipsechaser 05] for astronomical applications of this type of panoramic
camera.