698
PHOTOGRAMMETRIC ENGINEERING
A
DESK TYPE CAMERA CALIBRATOR
This instrument, in the design stage, is
meant to furnish calibration negatives by
a simple photographic procedure.
Exposures of the calibration targets are
intended to provide file negatives of nonmetrical cameras from which focal length,
principal point location, radial lens distortion, tangential lens distortion and
resolution may be determined, in the event
that significant' photographic data obtained with hand held cameras' requires
metrical analysis.
THE COLLIMATING CAMERA CALIBRATOR,
the calibration of amateur and other hand
held cameras. This calibrator employs a
single objective lens and an array of pinholes situated at the curved inside surface
of the objective lens.
The trend toward miniaturization and
integration is very well shown here: The
instrument combines both the functions
of a calibrator and those of a fully fledged
optical bench". In spite of this amalgamation of functions, the device occupies less
space than either of its predecessors taken
singly, and its capacity includes all the
visual and photographic functions of these
latter.
This is a simple instrument adapted to
THE MULTISCOPE IN RETROSPECT
Stephen H. Spurr, Professor of Silviculture, School of Natural Resources,
University of Michigan
T
HE Multiscope has now survived
nine years as an unique device in the
field of photogrametric instrumentation.
Classically, the use of aerial photographs
has been divided into two rather distinct
fields: (1) photogrammetry, the more or
less precise measurement of aerial photographs; and (2) photo-interpretation, the
visual estimation of what can be discerned
from the stereoscopic image. The Multiscope fits into neither of these fields. It is
neither a precise mapping instrument, nor
is it a crude and portable ,photo-interpretive device. Rather, it fills the need for a
large and growing number of specialists
who use photographs in their everyday
work and who require reasonably accurate
but low cost maps. These men include
foresters, to whom photographs are now
basic tools in their work; civil engineers
and surveyors, who have not gone into
precise geometric measurements and yet
who increasingly find photographs almost
indispensable in their activities; soil scientists and geologists, who also are relying
more and more on photographs as a basic
tool; and such general land-use specialists
as geographers, to whom photographs are
equally important. There are several
thousand such specialists in this country
and many more around' the world. In
forestry alone it is estimated that more
than 3,000 professional foresters in the
United States use photographs in their
every-day professional activities. Yet, few
of these foresters are professional photogrammetrists, and few work in offices or in
organizations that have gone into precise
photogrammetric equipment.
The Multiscope, then, is designed to be
a flexible multiple-use instrument suitable
for use by men who desire to make reasonably accurate use of aerial photographs,
but who do not desire tD go into, or who
are not trained in the use of the more precise photogrammetric devices, Basically,
it is simply a combination of a mirror
stereoscope and a camera lucida in a flexible and adjustable frame, Figure 1. By
interchanging full-surfaced and partiallysilvered mirrors, it is possible to use the
instrument as (1) a mirror stereoscope, (2)
a simple camera lucida, (3) a stereoscopic
plotting transfer device. The use of simple
lenses and of various settings for the individual mirrors and the entire mirror assembly permits the enlargement or reduction of photographic scale up to two and a
half or three times. This means, for instaIlce, that a forester can work with aerial
photographs at a scale of 1: 15,-840 on one
job, and transfer his forest ,type information on to a U. S. Geological Survey Topographic Map Sheet at a scale of-I :31,680.
At another time, he may use the same
photographs and the same instrument and
NEW DEVELOPMENTS IN PHOTOGRAMMETRIC EQUIPMENT
699
FIG. 1. The Multiscope being used in direct forest type mapping in a district forestry office.
transfer his forest-type information on to a chusetts. Actually, it now appears that the
large plan of his forest at a scale of 1: 7,920.
need for such an instrument was felt in
Or again, if the photographs have been de- several parts of the world, and that several
lineated with a grease pencil, he can use the others about the same time independently
Multiscope as a simple camera lucida to evolved very similar instruments. At least
transfer the type lines. On the other hand, . three such devices have been brought to
should he be working with borrowed the attention of the writer, all of which are
photographs that he cannot mark, he can similar in principle and application to the
use the M ultiscope as a stereoscopic plot- present Multiscope. In any event, the
ting device and type directly on the map Multiscope is the only one 'of these devices
without making any marks on the photo- that is currently in production.
graph whatsoever. It is this flexibility and
In summation then, the Multiscope has
variety of use that has made a place for held its place as an instrument intermethe M ultiseope in forestry and geology diate between the typical photogrammetoffices around the world.
ric and the typical photo-interpretation
Historically, the Multiscope was con- devices. Providing in one instrument a
ceived by George R. Sonley and the writer combination and flexible stereoscope and
in Ottawa, Canada* in the spring of 1945. plotting device, it has found wide use
In the form it is now manufactured, it was among professional men who use aerial
evolved by the writer and C. T. Brown, Jr.
photographs in their every-day operations
at the Harvard Forest, Petersham, Massa- but who do not pretend to be professional
photogrammetrists.
* Canadian Patent No. 460609.