The detection of shadow marks, as noted previously, may require a very 
low sun angle. In such instances, early morning or late afternoon photog 
raphy may be required, especially in the lower latitudes. For most vertical 
reconnaissance photography, however, a high sun angle is desired to minimize 
shadows and to obtain maximum illumination of terrain features. This is 
especially important for producing correctly balanced color photographs, be 
cause underexposure is a common problem with some color emulsions. 
When scheduling midday photographic flights in the lower latitudes, pre 
cautions should be taken (especially with wide-angle camera lenses) to avoid 
"hotspots" on the exposures. Such hotspots, or sunspots, result from the 
absence of shadows (light halation) and they may destroy the exposure detail 
on a portion of each photographic frame. Since hotspots occur near a prolon 
gation of a line from the sun through the exposure station (camera lens), 
their probable occurrence can be predicted—and avoided—by careful planning 
and timing of flights. 
Photographic Scale 
Here we must distinguish between reconnaissance flights covering large 
regions as opposed to detailed photography of known or excavated sites. In 
the first instance, scales of 1:10,000 to 1:20,000 have been successfully em 
ployed in several countries. This could be due to the fact that existing 
black-and-white photography in this scale range is available at nominal cost 
in many parts of the world. 
The potential of very small-scale imagery that is transmitted from earth 
orbiting satellites has not been fully evaluated from the archeological view 
point, but certain linear features such as ancient roadways and extinct stream 
channels have been discerned on such imagery. The author would be pleased to 
learn of additional uses of earth-satellite imagery from members of this orga 
nization. 
For photographing known, exposed, or excavated sites, photographic scales 
of 1:500 to 1:5,000 have been utilized by various investigators. Here, the 
scale specified is governed by the physical extent of the site and the degree 
of detail required. The extremely large scales are usually limited to sites 
being excavated or photogrammetrically mapped. For example, sequential ex 
posures obtained at various levels of excavation provide permanent records for 
the study of previous landscapes at successive periods of occupation. Used in 
this context, such imagery would effectively serve as "time-lapse" photog 
raphy of past cultures. 
Large-scale photographs are also required for compiling detailed maps or 
precise ground plans of certain structures such as burial mounds, fortifica 
tions, or Indian pueblo dwellings. In a few instances, the scale required is 
so large that helicopters or specially-constructed towers are required as 
camera platforms.