Small scale pictures (1:30 000) should be enlarged for prac- 
tical use, partly in order to permit a utilization of the high re- 
solving power provided by modern cameras and film, and partly 
to allow drawing on the pictures without disturbing its details 
too much. Moreover, persons using the photos may have reduced 
faculty of seeing or are not used to photo interpretation. The 
smallest scale hitherto used and regarded suitable for practical 
work'is 1:20 000. Pictures larger than 30X30 em are not 
practical to handle, especially for stereoscopic studies in field. 
From 2323 cm negatives, often used nowadays, it is possible 
to obtain 30X30 em enlargements in 1: 20 000 from photography 
scale 1: 30 000. 
It should also be considered that for high altitude photos there 
is a greater risk that haze etc. may reduce the picture quality. 
It is not advisable to conclude too much from the result of 
the investigations performed here. It may, however, serve as a 
guidance for the choice of photo scale in forestry. According to 
the investigations the scales 1: 16 000 to 1: 33 000 seem to be of 
practically the same use for normal forestry purposes. For the 
practical reasons mentioned above (the size of the enlarged pic- 
tures, etc.) it can be stated that, at present, the photo scale for 
practical work in Swedish forestry should not be smaller than 
1: 30 000. 
Summary. 
What photography scale is the most practical from the point 
of view of forestry and, especially, what is the smallest scale 
usable for practical work? 
These questions have become of current interest for several 
reasons in Swedish forestry and, therefore, the Committee of 
Forest Photogrammetry has carried out research work on photo 
scales. Measurements of tree heights by means of mirror stereo- 
scopes and stereometers and estimations of various stand factors 
have been done on enlarged pictures on scale 1: 15 000 from the 
photography scales 1: 16 000, 1: 26 000 and 1:33 000. (Camera: 
Wild RC5a, Aviogon 15.3 cm.) 
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