range. Modern photographic infrared films were
perfected by the early 1930s, and initially the appli-
cations of the films were for scientific and military
purposes. Gradually these films gained popularity
with artists and photographers, and they are readi-
ly available in most camera stores.
Infrared Film
Infrared films are made by adding certain sensitisers
to the film emulsion during the coating process. This
‘‘allows’’ the film to ‘‘see’’ the infrared spectrum. The
question is ‘‘exactly what does this film see?’’ The
answer is that it depends on what filter is used with
the film. Without any filter the film works as a coarse
grain, green sensitive (orthochromatic) emulsion,
and it is sensitive to the entire visible light spectrum.
By adding filters, starting with yellow (#12) and
going to orange and red (#25) or the infrared only
filter (#87) the film can ‘‘see’’ deeper and deeper into
the infrared range. The filters actually subtract or
block the visible light depending on the color of the
filter and therefore reveal more of the remaining
infrared light. The question is often asked if the infra-
red films can record heat and the answer is that they
cannot ‘‘see’’ heat. The reason is that the infrared
films record the infraredportion of thelight spectrum
reflectedfrom the subject being photographed, not
the thermal energy that the subject contains.
Light Spectrum
There are different theories that describe the light
spectrum. The one that makes the most sense for
photographers is the wave theory. This theory
holds that light is a wave and that you can measure
the length between the tops of the waves, similar to
waves in the ocean. The distance here is very short,
shorter than of one millionth of a meter. We call
these nanometers and the visible light spectrum sits
between 300 and 700 nanometers. Ultra violet is
about 300 nm, while red is 700 nm. Beyond 730 nm
is the infrared range, and its length is generally
defined as being between 730 to 1400 nm. The
commercially available films range in sensitivity
from 750 nm to 900 nm. Thus it becomes important
to select the right film for a given purpose or infra-
red effect. Kodak films are generally sensitive up to
the 900 nm range. Ilford SX-200 has a range up 750
nm, while Konica films reach into the low 800 nm
range. Since nanometers are analogous to horse-
power in an engine, the higher the number the more
infrared the film is potentially capable of recording.
The difference in the results then becomes the filter
that you apply in taking the photograph. The
stronger the filter, the more of the infrared infor-
mation that you will record on your film.Exposure
Infrared films do not have standard exposure sensi-
tivity such as an ASA or ISO. The reason is that the
film is sensitive to the amount of infrared radiation
that is reflected from the subject that you are photo-
graphing. So where does infrared radiation come
from? The sun is a massive source of infrared, but
as we all know, the amount of sunlight present can
vary depending on many factors, including weather
conditions, pollution in the air, time of day, and
season of the year. Other good sources of infrared
light are tungsten bulbs and strobe lights.
Some light meters and camera meters can read
infrared very well, others do not do so well, and
unfortunately none have an explanation or warn-ing in the directions that come with the meter.
Fortunately, the amount of infrared light that is
present is proportional to the amount of light from
the above sources.
The following are some recommended settings
for camera light meters that have proven valuable
and should serve as a starting point.
The method of taking an infrared photograph is
to take a meter reading without the filter on the
camera, set the proper exposure, and then put the
filter on the lens.Infrared Light and Lenses
There is another element to consider with infrared
and that is the wavelength itself. The lenses on
almost all cameras are made to focus the visible
light spectrum. Optically the lens must bend the
different rays (read different wavelengths) so that
only one image is formed on the film inside the
camera. This is quite an optical feat and some
older lenses could not do this. With infrared we
find that the wavelengths are even longer than the
visible light waves and that the normal rules no
longer apply. These waves in effect form an image
behind the camera when the camera is focused on
the visible wavelengths. In order to make an infra-
red image that is in sharp focus, we must actuallyKonica 750 in
the 2¼" film size ASA 32 without the filter
Kodak Infrared
High Speed HIE–35mm ASA 125 without the filter
Ilford SX200 ASA 200 without the filterINFRARED PHOTOGRAPHY