Film Camera Basics

The basis for traditional photography are light-sensitive chemicals in the film emulsion. Such photochemical imagery depends upon the reaction to light of silver halide crystals, which undergo a chemical change when exposed to ultraviolet (UV), visible, or near-infrared (NIR) radiation. This photochemical change can be developed into a visible picture. The sensitivity of chemical photography ranges from about 0.3 mmto0.9 mm wavelength. The lower limit is based on available UV energy and strong atmospheric scattering; film spectral sensitivity determines the upper limit.

Different parts of the spectrum may be photographed by using various films and filters. In fact, many film-and-filter combinations have been developed for routine and special purposes in aerial photography (Table 6-1). Photographs are routinely taken in b/w panchromatic, b/w extended red, b/w infrared, color-visible, color-infrared (Fig. 6-2), and multiband types.

Multiband photography is taking simultaneous photos in different portions of the spectrum. Early attempts at color photography in the 1890s were, in fact, based on separate b/w photographs in blue, green, and red bands that when viewed together simulated natural color (Osterman, 2007; Romer, 2007). Another variation is four-band photography with separate b/w photographs in blue, green, red, and NIR bands. As an example, the Apollo 9 mission in 1969 included a photographic experiment in which four coaxially mounted Hasselblad 70-mm film cameras were used to simulate multiband imagery. These results provided a proof of concept for the technology employed in the early Landsat multispectral scanner (Lowman, 1999).

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