Fluorescence Photography

Theory

Photography of latent prints developed with fluorescent powders or dyes is not really different from photography with a strobe light unit or sunlight. The four elements of photography (film, light, aperture, and shutter) are still the same. The only difference is the type of light being used. Remember the photographer's adage, "if you can see it, you can photograph it."

The latent fingerprint which is fluorescing with the use of a forensic light source is viewed through filtered goggles; therefore, to take the picture, the same color filter must also be used on the camera. For example, if red goggles and the 570 nm wavelength setting on the Forensic Light Source show the best contrast latent print, a red filter on the camera and the 570 nm wavelength setting on the Forensic Light Source should also be used to take the photograph.

Camera Equipment

In the laboratory, cameras on a copy stand can be used, e.g., Polaroid MP-4 Plus. These cameras have the advantage of using large format film to be able to photograph a whole palm or several fingers on the same sheet of film in a one-to-one size. In the field, the most convenient and versatile camera to use is a 35 mm format camera. Regular crime scene photography can be done using this camera and, on the same roll of film, take photos of the latent prints. The latent prints should be photographed one-to-one or life size. If your 35 mm camera lens does not focus at 1:1, an adapter can be attached to produce a 1:1 negative. Because the exposures can be lengthy, a tripod is a necessary piece of equipment. The 1:1 lens adapter by Lightning Powder Company, Inc. can be used as a mini-tripod. Auto-focus cameras should be set for manual focus. A cable release is handy to avoid camera movement. For a larger format of 3 1/4" x 4 1/4", the Polaroid Spectra Law Enforcement Kit is an easy-to-use camera for this type of photography in the field. The Spectra camera fits on to a one-to-one copy stand which can be held against a wall or placed on any other surface or object.

Camera Filters

It is recommended that a set of three filters (orange, red and yellow) be obtained. In a pinch, a pair of goggles can be placed over the lens of the camera. We have found that the following commercially available filters give good results: Nikon 056 = orange, Wratten 29 = red and Wratten 15 = yellow. Quality filters from other manufacturers should also be acceptable. No filters are needed if a long wavelength ultraviolet setting is being used.

Film

Most types of films used for general crime scene photography can be used for fluorescence photography.

It is not necessary to remove the partial roll from the camera while shooting a crime scene to change to a special roll of film. Black and white, panchromatic film or color slide or color negative films can be used. No special darkroom processing is needed. Polaroid slide films work very well in crime scene situations because they can be processed immediately at the scene to examine the results. Any brand of slide film is beneficial in fluorescence photography as it can be printed on regular black and white photo paper and the resulting latent prints will be black in color on a light colored background.

Exposure

As with any close-up photography, a medium to small ƒ/stop should be used. Suggested ƒ/stops are ƒ/11 or ƒ/16. The shutter will be set on "B" for bulb or on "Auto," if using an aperture-priority automatic camera. When using the manual setting of "B," knowledge of an appropriate time exposure is needed. Some experimentation before going to a crime scene is necessary. Even at the crime scene, it is wise to bracket the exposures. For example, using an Omnichrome® OP-1000a forensic light source set at 485 nm, with Blitz-Red™ and Blitz-Green™ fluorescent magnetic powders, an orange viewing filter and an orange filter (Nikon 056) on the camera, an Olympus OM-2N with a 50 mm lens, a Lightning 1:1 lens adapter and Polaroid Polapan slide film (ASA 125), an excellent exposure was produced at 5 seconds at ƒ/16 (see photograph below). We bracketed the exposure at 2 and 8 seconds. We also tried using the automatic exposure mode of the camera and achieved excellent results at ƒ/11 and ƒ/16. We repeated the exposures using Ilford XP2 black and white film (ASA 400) with outstanding results. The automatic mode of the camera gave the most consistent exposures. A suggested starting exposure is ƒ/16 at 2 seconds. Remember, negative film must be reversed if black ridges for the latent print are desired.

An example of Polaroid Polapan slide film printed on Kodak Polycontrast Rapid II RC black and white photo paper. The latent print on the left was developed with Blitz-Green™ fluorescent magnetic powder and the one on the right was developed with Blitz-Red™ fluorescent magnetic powder.

Scales

It is always wise to include a scale in the photograph, even when using a 1:1 lens or 1:1 lens adapter. If challenged to its accuracy, the photograph can be proven to be the correct size by checking the scale. We suggest our 20 mm scales, as they are not too big to be included in a 1:1 photograph. It is always a bit difficult to squeeze a large ruler or scale into the picture and determine whether the lines are inches or millimeters. If the 20 mm scales are consistently used for all 1:1 photography, there is no question as to whether the lines are inches or millimeters.