| Summary: | Thesis (M.A.)--Boston University === Panoramic photography is quite old, but is becoming increasingly
important in the field of aerial photography. Due to
increased efficiency of aircraft warning facilities and accuracy of
anti-aircraft missles the problem of obtaining photographs for
aerial reconnaissance and mapping and charting becomes extremely
hazardous. The obvious solution is to fly higher and further away
and to take oblique photographs. This doesn't seem to be difficult,
at first glance, but the object to camera distance becomes extremely
long, thereby reducing the scale of the photograph. Decreasing
the scale of a photograph decreases its usability. The only way
to keep a proper scale then, is to increase the focal length. Increasing
the focal length increases the format size and the overall
camera dimensions, and more important weight. Weight and size
are at a premium in an aircraft and to combat this a folded optical
system is coupled to a slit scan device which utilizes moving film.
This reduces weight and size, but introduces other technical problems,
which are presently being solved by the U. S. Air Force.
Assuming that the panoramic camera is built and is operational
suitable. A method of rectification must be devised in order
to effectively utilize the photography. Three methods of rectification
are discussed. First, a pancratic lens coupled to a slit scanning
device. Second, a mechanical rectifier, utilizing moving film and paper. Third, a mathematical Solution.
The pancratic lens-slit scan system tends to recreate the
conditions in existence at the time of exposure. The Scheimpflug
condition is neglected by selecting a slit width so small that the image
remains within the focal range.
During the exposure the images were in perfect focus from
nadir to horizon, as the distances involved are considered to be
infinity. But in rectifier the object to image distance varies from
4 feet at the nadir to 6 feet at 0 = 60°. Therefore a lens system had
to be designed to keep proper focus for all object to image distances
and the proper magnification, (to insure the correct scale). These
two variables are a function of the angle of scan (0). The basic
design for this pancratic lens starts with selecting 2 lenses of 22
inch focal length and computing the movements necessary to accomplish
the required magnifications and focal distances.
It was found that this could be easily accomplished, but the
final lens system would have to be designed by a competent lens
designer and would be much more complicated, due to a aberration
corrections.
For proper illumination the filament of the light source has
to move as a function of 0 in order to keep imaged onto the aperture.
The effective f/no very nicely stayed approximately the same,
14.75 to 17.25, throughout all the lens movements.
For overall illumination the speed of the scan has to vary
to compensate for loss due to the inverse square law, due to tilting
of the image plane, and due to increased density of negative toward
the horizon.
The second system, the mechanical system, consists of
either a pancratic or a fixed lens system, with the negative moving
past a slit and the image being projected down on a table onto moving
paper.
The moving parts that have to be calibrated are: the negative,
printing paper, light source filament, 1st projection lens, 2nd projection
lens, rotation of lens system, image to object distance, and
tilt of easel. Most of these relationships are easy to compute and
control, but the paper speed when determined will be difficult to
control. As has been observed in the field , continuous printing devices
do not operate efficiently in operational organizations.
The third system, the mathematical solution, uses surfaces
which were derived by trial and error after extensive mathematical
research. This system can be proved, mathematically, not to be
perfect. In fact the distortion has not been reduced less than 14 per
cent. This is too much for reconnaissance and charting purposes.
In view of the limitations of the various rectifiers it is felt
that the pancratic lens-slit scan system would be the most practical
rectifier for field use.
If accepted for field use this pancratic lens system could
eventually replace the current tri-metrago method of charting.
The panoramic rectification system would eliminate many operations
and specialized techniques and save money by reducing man-power
requirements per chart.
|
|---|
