To understand the potential of infrared, one must first conceptualize the way in which it both records, and alters our visual perception of the world. A schematic of the Electromagnetic Spectrum shows the range of electromagnetic radiation, from ultraviolet at the far left to radio waves at the far fight. At any given time there are varying amounts of every wavelength. Humans, however, perceive only the visible range, which might better be called the "hominid" range, since many animals see much more of the total spectrum. Appropriately, film manufacturers have designed black -and-white emulsions to record the hominid part of the spectrum. Black-and-white panchromatic films do this with exquisite fidelity. Unfortunately, hominids are used to seeing the world in color. When that world is reduced to gray tones, many of the subtleties of hue disappear. As a result, photographers and film manufacturers alike have sought ways to enhance visual contrast in black and white photographs.

There are many ways to accomplish this. Photographers use the Zone system to separate the tonal relationships in the final print through negative exposure and development. An alteration of visual reality is used to enhance visually a salient detail or to elicit an emotional feeling from the viewer. A second way involves the use of films which inherently possess the contrast and spectral sensitivity necessary to heighten visual contrast. To illustrate this point, imagine making three separate photographs of a tree in a bare field against a clear sky. A panchromatic film, such as Kodak T-Max 100; a film with extended red sensitivity, such as Kodak Technical Pan; and infrared film, such as either Konica 750 Infrared, Ilford SFX 200, or Kodak High Speed Infrared are exposed through a red filter to increase the overall visual contrast. However, the panchromatic film obtains less contrast between the sky and ground than the other films used. Technical Pan film establishes greater visual separation between the sky and the tree, but the Konica 750 Infrared, Ilford SFX, and Kodak High Speed Infrared films separate the tree from the sky best of all. This comparison illustrates the difference inherent film properties can have on the visual contrast in the final print. Both Technical Pan and Infrared films possess higher shadow contrast than a panchromatic film like T-Max 100. That is, for each quantum of shadow exposure, there is a disproportionately greater increase in negative density than would be expected. This affects the separation between the ground and the tree and results in higher visual contrast. Infrared film separates the tree strongest of all three due to reflected infrared radiation from the green parts of the tree containing chlorophyll and the absence of infrared radiation in the sky. Using a film sensitive not only to visible but also to infrared radiation expands the contrast range of the negative, which the viewer observes as heightened separation between light and dark areas in the final print.

Imagine, the infrared vs. panchromatic renditions of green, leafy trees against a deep blue sky. Again, there is increased visual contrast in the infrared image. The leaves appear nearly pure white, whereas the sky has been rendered nearly black. This is due to the film's sensitivity to infrared radiation, which is strongly reflected by chlorophyll in the leaves. Skin tones, dye pigments and fabrics are also rendered with higher visual contrast, that is, lighter. Skin tones, in particular, are rendered lighter, because the arterial blood flow to facial capillaries strongly reflects infrared. Thus, the infrared properties of both high shadow contrast and sensitivity to radiation beyond the visual range of our eyes make it an excellent candidate for applied photography. The Eastman Kodak Company[9] has published a number of technical bulletins describing many applications, and they are referenced at the end of the article. For this reason, only a few applications will be mentioned.

The scientific application of infrared photography is aptly demonstrated in archeological research. Faded, faint pigments found in rock art have been recorded and visually strengthened. The enhancement of the Dead Sea Scrolls is another excellent example of this application. In fact, a growing number of disciplines benefit from the selective visual enhancement made possible by infrared. Many plant pathologies can be detected using aerial mapping of suspected areas. Since chlorophyll is affected by disease, darker areas in infrared images point to pathology. But by far, forensic science has benefited the most from infrared imaging in the areas of investigative documentation. Gunpowder burns and arson accellerants are quite visible in infrared, as well as pigments found in inks. The legibility of forged documents as well as burned paper can also be enhanced by infrared imaging

The practical use of infrared film is predictable, in an atypical way. Since our visual perception is opaque to infrared radiation, determining exposure can be tricky. You can use a light meter to obtain fairly accurate readings....so long as you remember what kind of light source you are using. In general, daylight (strobe) sources emit less infrared than do tungsten sources. Unfortunately, your light meter doesn't measure the percentage of infrared vs. visible, hence the problem.

Exposure indices (E. I.) for infrared films are based on using a filter over the lens, contrary to normal films. If you are using through-the-lens-metering on the camera with the filter attached, your camera will compensate for the loss of light absorbed by the filter, and prompt you for increased exposure. The result will be over exposure to the negative. To eliminate this problem, you must calibrate your camera's metering system with the filter to the working speed of the film.

To do this set the film speed into the ASA/ISO dial of the camera. With the filter off the lens, make an exposure reading of a uniformly neutral subject, e.g., gray card, palm of your hand. Center the needle in the viewfinder. Without moving the camera, place the filter over the lens and again meter the same scene. If the needle deflects, you must change the ASA/ISO setting on your camera until the needle again rests on the same spot. Once completed, you will be able to meter the scene through the filter.

Published speeds for Kodak High Speed Infrared are significantly increased when processed in Kodak TMAX-RS developer. Although not listed as the recommended developer, it produces maximum film speed and can be prepared right from the bottle as a single shot developer. TMAX-RS comes with a packet of starter, affectionately called "Part B." Instead of making a working solution by pouring "Part A" into a volume of so much water, adding "Part B" and then topping off to a specific volume of water, I suggest you put the starter directly into the bottle of Part A. Agitate the container for about one minute to mix thoroughly. The dilutions included in the table at the end of the article are then derived directly from the concentrate. For instance, a 1:9 dilution means one part TMAX-RS concentrate to nine parts water; or 100ml TMAX-RS plus 900ml de-ionized water to make a working solution of 1000ml.

Always used de-ionized water. Excessive amounts of dissolved chlorine can cause pinholes. And since the amount of dissolved chlorine fluctuates greatly across the country, you are strongly advised to use de-ionized water for the preparation of presoak as well as all developing solutions.

In addition to Kodak High Speed Infrared films that are available in 35mm, 70mm, 4x5, and 8x10, Konica Infrared 750 is another film that is sensitive to infrared radiation. It is available in both 35mm and 120. Ilford SFX 200 is available, at this time, in 35mm only. While neither is a true infrared sensitive film, like the Kodak High Speed Infrared, both Konica and Ilford possess fine-grain characteristics and response to TMAX-RS as well as HC-110 developers make it an alternative.

Kodak High Speed Infrared can also be reverse processed to a transparency. Kodak T-MAX 100 Direct Positive Film Developing Outfit was released in 1989. Ostensibly designed to reverse process T- MAX 100 and Technical Pan films, this product can also be used to reverse process Kodak High Speed Infrared film to a black-and-white transparency.

Learning to use infrared requires experimentation both in processing and visualization. Infrared's far red spectral sensitivity requires getting used to before any visual predictability can be obtained. This learning phase can be greatly shortened by using the 35mm version and reversing the films to transparencies. Since a slide represents a "What-You-See-Is-What-You-Get" view, exposure calibration and visualization can be evaluated as soon as the transparency can be projected. Rather then processing the films to negatives first and then contact printing them, the user can test out exposure, lighting, filtration, and subject matter and see the result in far less time than it takes to look at the final contact sheet. This gives the user instant feedback--a critical component for grasping both the intricacies and potential of these films.

For technical applications of Infrared film, this is an especially attractive process. Imagine the obvious advantage of first testing different clothing, backgrounds, and lighting to previsualize their effect when using infrared. Fashion, commercial and architectural photographers can produce a reasonably quick assessment of an assignment and present the results to a client in short order. In addition, the scientific community can especially benefit from this process, because of the ease with which a positive transparency can be obtained. For instance, survey recording of archaeological sites in infrared often reveals details invisible to man's limited spectral range. Transparencies can permit a quick evaluation, can be shown to large audiences, and can be converted directly into publication prints.

Another aspect of the reversal process is a significant increase in effective film speed. For example, using infrared with a red (Wratten #25) filter in daylight (strobe) results in an effective E.I. of 200 when processed to a negative. However, processing the film as a transparency under the same conditions will result in a E.I. of 640! Imagine the potential using the film without a filter, in tungsten light. You are now talking about an effective speed around 2400!

The procedure for reversing Infrared is simple and easy. The processing kit contains all liquid components. A slight modification of the first developer will increase contrast and result in a higher maximum density. Simply add 45gm Sodium Sulfite (Anhydrous) to the first developer when mixing. Follow the instructions in the kit. A one minute presoak in de-ionized water is used prior to the first developer. Use the same processing times listed in the kit. Figure 7 provides starting point exposure indices for Konica Infrared 750 processed to a negative and for Kodak High Speed Infrared Film processed both to a negative and a transparency.

With the infrared products and processing chemistry available today, photographers from very different fields of study have a very powerful tool available to them. Applied photography is merely the skillful blending together of science and art. While specific applications have changed over time, it remains for the alert investigator to recognize a new application which takes advantage of this film's spectral sensitivity and to create a new visual paradigm.

  Light			   Exposure
  Source       Filter	    Index     Developer	  Dilution   Temp.      Time
*Daylight	red (25)     200       TMAX-RS	    1:9	      70°F	8 min
 (Strobe)
*Daylight	none	     400       TMAX-RS	    1:9	      70°F	8 min
*Tungsten	red (25)     400       TMAX-RS	    1:9	      70°F	8 min
*Tungsten	none	     800       TMAX-RS	    1:9	      70°F	8 min

Konica Infrared 750 Exposed and Processed as a Negative

  Light		       	   Exposure
  Source       Filter	    Index     Developer	  Dilution   Temp. 	Time
*Daylight	red (25)       8       TMAX-RS	    1:23      70°F	5 min
  (Strobe)	
*Daylight	red (25)       8        HC-110	     F	      68°F	7 min
*Daylight	none	      16       TMAX-RS	    1:23      70°F	5 min

Kodak Infrared Exposed and Processed as a Transparency

  Light			   Exposure
  Source       Filter	    Index     Developer:  TMAX Reversal Kit
    (add 45 gm sodium sulfite to first developer)
*Daylight	red (25)     640       TMAX reversal kit      (See kit instructions)
  (Strobe)
*Daylight	none	    1200       TMAX reversal kit                  "
*Tungsten	red (25)    1200       TMAX reversal kit                  "
*Tungsten	none	    2400       TMAX reversal kit                  "

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