Full text: Transactions of the Symposium on Photo Interpretation

SPECIFICATIONS FOR MIRROR STEREOSCOPES 
by S. A. Hempenius 
International Training Centre for Aerial Survey, Delft, The Netherlands 
Abstract Specifications for mirror stereoscopes are given for the properties connected with 
image formation, image recording, image quality and operational, mechanical, and econom 
ical aspects. The measurements are explained briefly and the results for a number of stereo 
scopes are discussed. No single figure or formula for the overall performance is given; the 
user is asked to weigh the various aspects and qualifications according to his needs. 
Résumé Les particularités des stéréoscopes à miroirs touchant à la formation, à la percep 
tion et à la qualité des images font l’objet de spécifications qui couvrent aussi le système 
mécanique, le mode d’opération et l’économie d’emploi. Des explications sont données au 
sujet des mesures. Les résultats concernant divers stéréoscopes sont discutés, mais aucune 
tentative n’est faite de représenter la valeur pratique globale de chaque instrument à l’aide 
d’un nombre unique ou d’une formule. Il est laissé à l’utilisateur d’étudier séparément les 
divers aspects du problème, de voir lesquels lui importent vraiment, et de trouver ensuite 
quel stéréoscope répond le mieux à ses besoins particuliers. 
Zusammenfassung Nähere Angaben über Spiegel-Stereoskope und deren Eigenschaften 
bzgl. Bildformung, Bild-Registrierung, Bild-Qualität, sowie operative, mechanische und 
ökonomische Gesichtspunkte werden besprochen. Die Messungen werden kurz erläutert und 
die für eine Anzahl von Spiegel-Stereoskopen gültigen Ergebnisse werden gemeldet. Es wer 
den keine einzelnen Ziffern oder Formeln bzgl. der allgemeinen Leistung gegeben; der 
Benützer wird angewiesen, die verschiedenen Gesichtspunkte und Qualifikationen seinen 
Bedürfnissen entsprechend gegeneinander abzuwägen. 
Why are specifications necessary? As the interpretation of aerial photography 
becomes more important, more attention must be paid to the stereoscope, in 
order to obtain a better idea of the possibilities and limitations of the inter 
pretation of aerial photographs. 
Specifications for Whom? For interpreters who need a better understanding 
of their key-instrument. Therefore we will consider the performance of stereo 
scopes from the user’s point of view. 
Specifications of What? Of Optical and Operational Properties. We will only 
measure how the instrument influences the observation of the object (paper- 
print) and whether it is convenient in use. We are not concerned with how it 
is designed, what special solutions and materials are applied and how it is 
produced. 
How to obtain Specifications? Considering the stereoscope as a “black box”, 
we do not need an exploded view of the optical and mechanical parts. The 
only way to arrive at specifications is to establish the properties of interest to 
the user, then to point out a way of measuring them and finally to judge the 
results (fig. 1).
	        
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