Proceedings of the fifth mountain lion workshop: 27

38 PROCEEDINGS OF THE FIFTH MOUNTAIN LION WORKSHOP
Broad bands of synthetic rubber covered the openings and held
the flash units in place. We found that a hole in the side of the
box, large enough to admit a flashlight was very helpful in
aiming and focusing the camera. The hole was covered with a
synthetic rubber flap to block sunlight. Lacking such a hole,
the camera may be focused by resting the camera case on top
of the box, with the lens pointing downwards outside of the
box.
Schematic drawings of the box and a materials list are
available for those who wish to construct their own "black
box." We suggest using thin foam padding glued around the
hole to support the camera body evenly so that buttons and
levers on the camera body do not cause imbalance and
movement. Individual experimentation is advised prior to
collecting field data, because variations may occur in power of
various flash units and photographic quality of material used to
filter the flash intensity.
For experimental purposes we used tracks made by a
live dog (Canis familiaris), and in some cases, tracks were
made using silicone molds from mountain lion (Felis concolor)
tracks. These tracks represented different substrates and
different depths in each substrate. We considered track
impressions to be "shallow" between 1 and 3 mm, of "medium"
depth from 3 to 7 mm, and "deep" when the impression was
more than 7 mm. Substrates included silt, sand, and gravel
(USDA soils definitions from Buol, Hale, and McCracken,
1973). Gravel sizes were in the 2 mm to 4 mm size range.
'Light-colored" substrates included fine silica sand, similar to
beach sand. Other substrates included sand like that found in
desert washes and gravel from decomposed granite.
We photographed the tracks using one flash or two
opposing flashes placed at each of the three heights. The flash
units were aimed either horizontally or downwards toward the
track. We then selected the best combinations of substrate,
depth, and flash arrangement/height using criteria described
below. Once we established the best physical arrangement for
the flash units, we experimented with different filters on the
camera lens and on the flash units. Lens apertures of F11, F16,
and F22 and shutter speeds of 1/60 second and 1/125 second
were used in conjunction with the filter and flash arrangements.
The tests reported here were conducted using settings of F16 at
1/60 second. We evaluated the results visually, selecting slides
that showed the best detail in areas of the track critical to
digitizing the track outline.
RESULTS AND DISCUSSION
Aiming and focusing the camera was not a problem.
The outside-the-box procedure described above was sufficient
for focusing in the relatively flat areas we used. Our lens and
distance combination effectively covered most of the area
enclosed in the box, so that if the track was reasonably close to
the center of the box, it was near the center of the picture.
Tracks comprised only a small part of the photograph. A larger
track image would be preferable.
We were able to maintain picture quality by
increasing flash height as track depth increased. We suggest
varying flash height from 2 inches for tracks 1-3 mm deep to
4 inches for tracks 3-7 mm deep, and either 4 or 6 inches for
deeper tracks. Details were more distinguishable when flashes
were aimed horizontally as opposed to being aimed at the
track. These relationships were consistent in all substrates.
However, on light-colored substrates (e.g., silica sand) a
single or double layer of window tint was needed over the
flash units to decrease light intensity. On dark substrates, such
as damp sand or gravel, no flash filters were needed. No flash
filter is needed for medium or dark substrates. Either a
polarized, neutral gray, or a yellow lens filter may be used on
all substrates, and one of them or a red filter, is necessary on
light substrates. A faster film with less contrast may show
more detail in the shadows. Any variation in film speed will
require adjustment of filters.
The choice of a lens filter depends on reflectance of
the substrate. With light-colored substrates, we could not
close the aperture enough to prevent overexposure, and a filter
was necessary. A circular polarizer seemed to improve picture
quality most of the time. A neutral filter was only slightly less
effective. A yellow lens filter improved picture quality on
dark substrates, while a red filter made the pictures too dark
on medium to dark substrates. On light substrates, either color
worked well. Either colored filter used in combinations with
a polarizing or neutral filter made pictures much too dark.
Some observers who viewed the pictures liked those taken
with colored filters, while others liked those taken with a
polarizing filter. The quality was good with either one, and
differences were minor.
We found little difference among the various
apertures perhaps because we had to many confounding
variables. We consider our experimentation in this area to be
incomplete. We used a wide-angle lens. It is possible that a
longer lens or a zoom lens may provide a larger track image
in the photograph. Different lenses may require a different
height dimension in the box. Also, a different distance from
the track to the camera lens will alter the exposure needed
because distance dilutes the amount of light that reaches the
lens.
Using a standard distance from the track to the
camera focal plane standardized the sizes of the tracks in the
photograph and made subsequent measurement and analysis
easier. We did place a standard-sized (one inch or one
centimeter) square card near the track so that people using
image-processing software would have a means for calibration
in the picture. The more important benefit of a procedure like
ours is to standardize quality of the photographs. We
experienced difficulty in finding the proper exposures for
different substrates, and some of our experiments provided
photographs in which the tracks were difficult to distinguish.