APPLICATION OF SPECIALIZED EMULSIONS SOURCES OF RADIATION

Unusual renditions of otherwise dull or mundane subjects is sometimes possible through the use of emulsions not intended for standard photography or by photographing using radiation other than light to illuminate the scene.

Ultraviolet Fluorescence photography-
The use of Ultraviolet radiation for special purpose photography is mostly restricted to fluorescence effects where a subject naturally fluoresces or is painted or coated with a fluorescing material, illuminated with a long wave UV source and the glowing, fluorescent colors are then photographed, typically against a dark, nonfluorescing background, using color film. In this nonscientific application, usually no great care is taken to exclude UV from the final record but it is nevertheless useful to point out that to obtain photographs uncontaminated by blue, a "barrier" or UV absorbing filter should be placed over the camera lens. Light sources used for this type of photography vary widely but electronic flashes filtered with a filter such as the Wratten 18A are typically good sources of UV. Modern flash units often have an incorporated UV absorbing filter and may not be as efficient as other (typically older), uncoated, tubes in terms of usefulness as sources of ultraviolet energy.

Infrared Photography-
The use of emulsions sensitive to Infrared wavelengths can be used to advantage for special effects purposes to emphasize certain aspects of subjects such as their Infrared reflectivity. Infrared sensitive emulsions are used in the field of special effects because of the sometimes unusual tonal reproduction of subjects as opposed to their appearance in normal black-and-white and color photographs. Since IR is not a visible part of the electromagnetic spectrum it cannot be spoken of as yet another "color", but it is true that the near IR wavelengths to which emulsions can be sensitized will often result in startling tonal reproduction of familiar subjects. The reason is simply that a subject's reflectivity of IR wavelengths does not necessarily equal the subject's reflectivity of visible light wavelengths.

Infrared tends to produce images of human skin that are very light in tone and also that have a slight "aura" or glow to them. The light tone is attributed to the high IR reflectance of human skin while the perceived "glow" is due to a combination halation and overexposure of the skin surface.

Although only available on a limited basis, there is a "false color", infrared sensitized reversal color emulsion, that is used for aerial photography and remote sensing applications. This film is sometimes used as a special effect film applied to more normal subjects in order to impart an unusual color reproduction to an otherwise normal subject. In this emulsion one of the layers is sensitive to infrared, while the other two are green and red sensitive respectively. The film typically should be used with a blue-absorbing filter because all three layers are also blue sensitive.

Date: 2016-01-03; view: 748