Operating Instructions—C-30B Camera
PREFOGGING. A method which sometimes produces
very good results w ith Polaroid Land films is prefogging. In
prefogging, the film is first exposed to a predetermined
amount of light for a definite period. The intensity of the
light and the period o f the exposure are so chosen that the
film is brought just to the threshold of being exposed. A
lesser amount o f light is then required to expose the film .
The prefogging technique can produce an increase in
maximum w riting rate o f two or more times, depending on
film types, film condition, the nature of the prefog light,
and other variables. Prefogging results in a slightly foggy
background on the photographs, w ith somewhat less
contrast. This is sometimes a small price to pay for a large
increase in w riting rate. A w riting speed enhancer is avail-
able to perform this function, see tabbed Accessories page
at the rear of this manual.
POSTFOGGING.
This is very similar to prefogging. The
difference is that the film is exposed to the controlled light
source after exposure, rather than before. Postfogging
produces very nearly the same increase in writing rate as
profogging. The writing speed enhancer can be used in post-
fogging to increase the w riting rate.
TRAIMSILLUMIIMATION.
While not strictly a means of
improving w riting rate, transillumination permits better
viewing of the Information recorded on prints. In the
technique of transillumination the p rint is observed w ith a
source of bright diffused light, such as a light bulb, directly
behind the p rint (see Figure 2-12). The light passing
through the p rint brings out detail which would not other-
wise be evident. The transillumination technique w ill not
work on films, which have an opaque plastic base.
Figure 2-12. Using transillumination to see otherwise invisible
Information.
CONTINUOUS TONE (GRAY SCALE) DISPLAY.
Photographing a continuous tone (gray scale) display
requires a technique different from that used for trace
recording. In trace recording, it is necessary to record two
levels of intensity—white for trace and graticule, black or
gray fo r the background. In gray scale photography, it is
im portant to record a whole ränge of tones that may be
only slightly different from one another.
A common problem when taking photographs of a
continuous tone display is that the print develops w ith a
loss of detail in the dark and light areas. A contributing
factor relates to the difference between the human eye and
film print reproduction. The eye is extremely sensitive with
a wide dynamic ränge that accommodates (within one
scene) brightness intensity ranges approaching 1000:1.
Polaroid Type 0847 or 667 film have a usable ränge of
approximately 15:1. Polaroid Type 611 has a wide bright
ness intensity ränge and is recommended for gray scale
photography.
There is quality gray scale tonal rendition when the film
print renders information in both the darkest and lightest
area of display presentation. Crt photography allows
adjustment of camera shutter speed, aperture opening and
instrument contrast to produce an acceptable photograph.
Adjusting the instrument so that the display appears low in
contrast, or "washed o u t" w ill merge the brightness (light
intensity) of the display fo r better film reproduction. This
adjustment compresses the display brightness w ithin the
recordable ränge of the film . Once this is set, adjust the
camera shutter and aperture control to obtain details in the
darkest areas of interest. Generally, this process w ill require
experimentation to produce satisfactory results.
Conventional Film
The matte-finish sprays referred to previously for mark-
ing Polaroid film are also good for coating Standard prints
and negatives fo r marking purposes. Remember that any
mark on the negative may appear on the print. This suggests
the idea of marking notes on the negative prior to printing.
The paragraphs on prefogging, postfogging, and contin
uous tone display Polaroid film apply equally to con
ventional films.
To increase the contrast of conventional films, the film
may be left in the developer longer or the temperature of
the developer may be raised; however, this may result in
increased grain and fog.
2-14
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