Exposure Compensation for Bellows Extension
As discussed in chapter 4, an exposure calculated
with an exposure meter is precise only for a lens set at
a distance equal to one focal length When the distance
between the optical center of the lens and the focal plane
is greater than one focal length, an increase to the
indicated exposure is usually required. Before an
accurate increase in exposure can be applied by opening
the lens diaphragm, the effectiveness of the f/stop of the
indicated exposure should be determined Remember,
the marked f/stops of a lens that is set beyond one focal
length are not valid because the f/stops are a ratio of the
diameter of the lens aperture to one focal length. Refer
to chapter 4 to determine how to compensate exposure
for bellows extension.
PROCESSING COPY FILMS
Films used for copying are processed the same as
any other film. They can be processed by machine or by
hand, using tanks or trays. Recommendations for
specific developers, developing times, and developing
temperatures are given with each type of film. Some
films not designed specifically for copying may yield
negatives with excessive contrast. This can usually be
avoided by reducing the developing time. Consult the
Photo-Lab Index to find suitable developing times to
lower or raise contrast.
CATHODE-RAY TUBES
Although taking photographic images from
cathode-ray tubes (CRT) is not actually a type of copy
work, it has become more commonplace to photograph
their images for briefs and presentations. Televisions,
computer monitors, and radarscopes all can be classified
as CRT photography.
When you are shooting CRTs, like all copy
photography, it is important for the optical axis of the
lens to be centered and perpendicular to the monitor. The
camera must be mounted on a sturdy tripod. A cable
release and a macro lens are recommended.
When you are photographing radarscopes, time or
shutter speed is not a factor of exposure. The number of
sweeps on the scope is the factor that determines the
exposure at a given f/stop. The number of rotations is
not proportional to film exposure. As a general rule, the
exposure doubles between one and three sweeps. To get
the correct exposure, you must bracket the exposure. A
good starting point for less than three sweeps with ISO
125 film is at f/5.6.
To get the sharpest and clearest image possible, you
must adjust the brightness of the radarscope correctly.
Do this by turning up the intensity until halos appear.
Then turn it down until the halos just disappear. When
the intensity of the scope is too great, the image appears
out of focus. If the intensity of the scope is not great
enough, there is little contrast between the video and the
background.
Computer-generated graphics are a common means
of producing material for use in slide briefings. When
available, use a computer monitor with a flat screen
rather than a curved screen Use the same procedures for
shooting computer screens that you use for radarscopes.
The difference is there is no sweeping motion when
shooting a computer monitor or a television. When
motion is apparent, you must use a shutter speed of
1/30th of a second. When you use this shutter speed, the
film records the image without obvious scan lines and
stops the motion of the image.
When photographing images from a CRT, always
darken the room before you make the exposures. This
prevents glare on the screen and only the illumination
from the screen affects the film.
SLIDE DUPLICATING
In photography, you must often make duplicate
slides from an original. Duplicating is actually a form of
copying. A duplicate or “dupe” can be made to almost
any desired size. Contrast and density along with color
adjustments can be made when duplicating color slides.
Color slides are duped to provide extra copies of the
slide, correct color balance and contrast errors, or even
to change or enhance colors for special applications.
CAMERAS AND ACCESSORIES FOR
DUPLICATING
Except for the copyboard or easel, the features of
the equipment used for duplicating transparent originals
are essentially the same as that used in copying
reflection originals. The exception being that the
copyboard for copying transparent originals must allow
light to be transmitted through the original to the camera.
Except for being lit by transmitted light, large
format transparent originals (larger than 35mm) are
copied the same as reflection originals. 35mm
transparencies are copied with special slide copying
attachments for cameras, or copied in specially
designed, semiautomatic or automatic slide copiers.
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