INTRODUCTI ON 
The value of a uniform-scale photograph upon which precise hori- 
zontal-distance measurements can be made without the necessity of applying 
corrections for image displacements due to tilt and relief has long been 
appreciated. Such photographs that retain the detail provided by the 
images appearing on a photograph and present this information in correct 
planimetric position, have been prepared from conventional perspective 
photographs. The instrument designed to effect this conversion is called 
an Orthophotoscope and may be defined, in general terms, as a photogram- 
metric restituting enlarger than magnifies the different images on a dia- 
positive inversely as their scale. The 1960 model Orthophotoscope is the 
third of a series of these instruments developed in the research laboratory 
of the U. S. Geological Survey under the direction of Russell K. Bean. 
The design of this model has benefited from nearly a decade of instrumental 
development and experience in the preparation and application of orthophoto- 
graphs. 
EARLIER MODELS 
The first Orthophotoscope referred to in earlier papers as 
the experimental or "bread-board" model, was completed in 1953.3/ 
Although considered crude, this first model served a useful purpose by 
demonstrating the soundness of the principles involved and the practicality 
of the design employed. The products of this first instrument were evidence 
that the images on perspective photographs could be restituted so that, 
for practical purposes, uniform-scale photographs were obtained. It was 
learned, too, that instrument stability was a more important factor in the 
preparation of orthophotographs than instrument portability. This finding 
ls reflected in the sturdier design of the subsequent instruments. 
The second Orthophotoscope, the engineered prototype, was fabricated 
in 1956. The value of the many improvements incorporated in this instrument 
was readily apparent in the improved quality of the resulting orthophotographs. 
This instrument has been operating on a full-time production basis since it 
was completed and many orthophotographs and orthophotomosaics have been 
prepared. Operational research led to the development of more efficient 
procedures. Operating practice and experience increased the skills of the 
personnel who prepared uniform-scale photographs. As might be expected, the 
cost of preparing orthophotographs was reduced and the geometric and photo- 
graphic quality of the product was improved. 
The orthophotographs prepared with this instrument were furnished 
to geologists, foresters, hydrologists and engineers to alleviate field 
mapping problems caused by the lack or inadequacy of map coverage in their 
areas of interest. From the comments and evaluations of users of ortho- 
photographs it was concluded that: first, when the benefits to be derived 
became known, the demand for orthophotographic coverage would exceed the 
capacity of this instrument; and second, that the purposes for which ortho- 
photographs may be effectively used and the methods that may be employed in 
their use were largely dependent upon the geometry and image quality of the 
orthophotograph. It was recognized that significant improvement in the 
quality of the orthophotograph was hindered by the mechanical limitations 
inherent in the 1956 instrument. Experience also showed that the physical 
discomforsts imposed upon the operator by the instrument were unduly fatiguing. 
For these reasons the procurement of additional Orthophotoscopes, improved me- 
chanically and designed with operator comfort as a prime consideratio, was advised. 
  
3 
Bean, R. K., Development of the Orthophotoscope, Photogrammetric 
Engineering, vol. XXI, No. 4, September 1955, 
  
2 
  
  
  
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