Articles from The Science Of Fingerprints
Radial And Ulnar Loops
Essentials Of A Loop
Chemical Development Of Latent Impressions
Types Of Patterns
The Use Of The Fingerprint Camera
If a fingerprint is visible, an effort should be made to photograph it
before any attempt is made to develop it. In every case a print
developed with powder should be photographed before lifting. It
sometimes happens that the print does not lift properly although it
may be quite clear after development.
The camera which is especially adapted to the purpose and which is
easiest to handle and operate is the fingerprint camera, one type of
which is shown in figure 424. This camera has several advantages in
It photographs the prints in natural size.
It contains its own light source.
It has a fixed focus.
Cameras of this type are available in models operated by batteries and
110-volt current. It is believed that the battery-operated type has
the greater utility, since house current may not be available at the
crime scene. When not in use the batteries should be removed as they
will eventually deteriorate and corrode the brass contacts in the
[Illustration: 424. The fingerprint camera.]
The camera is of the box type and has three button controls which will
open: (1) The metal flap covering the aperture, (2) the front portion
of the frame providing access to the self-contained light bulbs, and
(3) the camera in half, providing access to the batteries and the
shutter as shown below in figure 425.
[Illustration: 425. Button controls permit access to bulbs, batteries,
A 2-1/4 x 3-1/4 film pack adapter or a 2-1/4 x 3-1/4 cut film holder
holds the film in the camera. The film pack adapter will hold a pack
of 12 sheets of film, and accordingly, will permit the taking of 12
pictures. The cut film holder is a unit which holds two sheets of film
utilizing each side of the holder.
It is pointed out that the FBI uses the film pack exclusively in view
of the fact that practically all latent examinations will necessitate
the taking of more than two pictures. Further, the film pack is made
so that it may be loaded into the adapter in the open light. Also, the
films are numbered 1 through 12, which is a valuable feature in that
in maintaining notes concerning the latent examinations it is a simple
matter to note by the number of the negative where the latent
impression was developed and photographed. Should it happen that
during a latent examination all twelve of the films are not used, the
film pack, with the slide in place, is taken into the darkroom and
only those films which have been exposed are removed and developed.
The unexposed films remain in the film pack adapter with the slide in
and may be used later.
As was previously mentioned, the camera has a fixed focus; that is,
the camera will take a legible picture only when the latent print is
at the focal point, or exactly flush with the opening of the camera.
The latent print must not be inside the open end of the camera, nor
must it be beyond; otherwise, the picture will be blurred.
[Illustration: 426. When object being photographed does not cover
camera opening, outside light is excluded with piece of cloth.]
Since the camera has its own light source, any leakage of outside
light will cause overexposure of the film. Consequently, if the
surface of the object bearing the latent print which is to be
photographed is uneven or does not cover the entire front of the
camera opening, it will be necessary to use some opaque material such
as a focusing cloth or heavy dark material to cover the front of the
camera so as to exclude all outside light (fig. 426). If a latent
print on a pane of glass or an automobile window is being
photographed, it will be necessary to back up the latent so that there
will be no light leakage. Material showing a pattern or grain should
not be used for this purpose as any such pattern will photograph in
the background and possibly obliterate the ridges of the latent print.
To insure an equal distribution of the light over the latents being
photographed, the impressions should be centered in the opening of the
camera. This is accomplished by opening the angular front section of
the camera after the metal plate covering the front has been opened,
and setting the aperture over the latent impressions so that they will
be as near the center as possible. Then, holding the camera firmly in
place, it is carefully closed (fig. 427).
During exposure the camera must be held perfectly still. Any movement
of the camera or object will result in a fuzzy or double image.
In photographing a small, movable object such as a bottle or tumbler,
the camera should not be placed on its end and an attempt made to
balance the object across the opening. Instead, the camera should be
placed on its side and the bottle or tumbler built up to the opening
so that there is no necessity for holding the object (fig. 428). There
will be, of course, instances where the camera will have to be held,
such as to the side of a wall, cabinet or automobile. Here an extreme
effort should be made to avoid moving the camera or permitting it to
slip during exposure.
[Illustration: 427. Centering of latent in aperture insures equal
distribution of light over print.]
Anticipating the possible use of the photographic negatives in a court
proceeding, it becomes of paramount importance to be able to identify
them. This is done by using what is called an identification tag. The
tag consists of a small piece of paper bearing the date, initials of
the examiner, and possibly a case number, and it should be
hand-written. The tag is placed near the latent prints being
photographed so that it will appear in the picture. It should be borne
in mind that concentration should be on the latent impressions, which
must be centered, and the identification tag should be to one side and
not covering any of the latent prints. Another method of
identification, if the surface permits, is to write the
above-mentioned data on the surface of the object bearing the latents
so that the information set out will also be a part of the picture.
Too much emphasis cannot be placed on the importance of the
identification tag. The lack of such data, by discretion of the
court, may exclude the latents as evidence, in the absence of the
original specimen bearing the latents.
[Illustration: 428. In photographing objects with curved or irregular
surfaces, camera should be laid flat and latent-bearing surface built
up to opening.]
The following are suggested exposure times for Tri-X film (available
in 2-1/4 x 3-1/4 film packs) with battery-operated cameras having
lenses without diaphragms:
Black powder print on white or light background--snapshot
Gray or white powder print on black or dark background--1 second
These same exposure times can be used on some cameras having lenses
with diaphragms, provided the lens opening is set at f6.3.
The above exposure times are for cameras with batteries in average
condition. If batteries become weak the exposures may be increased
In making snapshots the shutter mechanism should be manipulated as
rapidly as possible since slow motion will appreciably lengthen the
exposure. In making time exposures the camera shutter must be held
open for the desired time. Personnel with photographic experience may
desire to use cut film with the fingerprint camera. A few tests will
determine the optimum exposure times for any particular type of film.
Briefly, the procedure for taking photographs of latents is as
follows: The film pack is placed into the film pack adapter with the
safety paper side of the film pack to the slide side of the adapter,
care being taken to see that all of the paper tabs are outside of the
adapter. The adapter is placed on the camera in its proper position by
opening a slide clamp attached to the camera, fitting the side of the
adapter into the slot away from the clamp and pushing it down flat
into the opening. Don't try to slide the adapter into the opening from
the top. The adapter is locked in position by closing the clamp. Next
the slide is removed and the tab marked Safety Cover pulled out as
far as it will come and torn off. The camera is placed in position and
the first exposure made; then the tab marked 1 is pulled and the
next film is in position for exposure. This procedure is followed with
each succeeding film until all have been exposed.
When the last tab has been pulled out, the pack can be removed from
the adapter in daylight. If all of the films have not been exposed the
slide is replaced into the adapter and the film pack removed from it
in a darkroom, as previously stated.
As a matter of regular policy, it is recommended that more than one
exposure be made of each latent, varying the normal exposure time to
insure satisfactory results, especially when the contrast is not a
good black on white or gray on black.
Before starting to photograph, note the following:
- Check shutter action.
- Check bulbs, batteries, and lights.
- Center latents in opening of camera.
- Latent being photographed must be flush with opening of
- Outside light must be excluded.
- Include identification tag in photograph.
- Remove slide and pull safety tab of film pack before
- Hold camera still while making exposure.
- Pull correct number tab after each exposure (be careful
not to pull more than one).
- Do not use grained or uneven material as a backing when
photographing latents on transparent glass.
- Mirrors, polished chrome, and nickel plate will photograph
black in the fingerprint camera.
The foregoing has dealt with the standard use of the fingerprint
camera when the direct light afforded by the camera gives suitable
results. There will be cases, however, where the results from the use
of the direct light may not be adequate. Such cases may involve molded
or embedded prints, such as prints in putty, wax, soap, etc. Should
direct light give poor results, side lighting may prove effective.
This can be done by loosening two of the bulbs on one side so that
they will not light. The light given by the other two bulbs is
directed so as to pass at right angles, as much as possible, across
the ridges of the embedded latent print. Adjustment of the exposure
time must be made when this is done.
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