Quartz-Iodine Lamps
The quartz-iodine lamps (tungsten-halogen) are of
the incandescent variety but bear little resemblance to
conventional light bulbs. A quartz lamp is a short tube
of quartz glass, housing a coiled filament that runs the
length of the tube. In ordinary tungsten lamps, the
tungsten evaporates from the filament and settles on the
glass and gradually darkens the bulb. In the
quartz-iodine lamp, however, iodine vapor combines
chemically with the tungsten and causes it to redeposit
on the filament. This prevents the tube from becoming
tarnished with age. The intensity and color temperature
of the tube remain almost constant throughout its life.
Although the quartz-iodine lamp is very small, it
produces intense light that is particularly suited for copy
work. There is a disadvantage-quartz-iodine lamps
generate extreme heat that could cause your original to
curl. You should never touch a quartz-iodine lamp with
your fingers. The oil from your hands can create a
concentrated hot spot on the lamp, causing it to bubble
and burn out.
LAMP REPLACEMENT.
­As lamps get older,
their color characteristics and light intensity may
change. Therefore, when one lamp in a set bums out, the
new replacement lamp is usually brighter and has a
different color temperature than the remaining lamps.
You should replace all the lamps, not just one to avoid
the need for adjusting the new lamp to get even
illumination. Replacement of all lamps in a set is
particularly important when you are copying with color
film because the color temperature of the new lamps is
higher than the old lamps. The variation in color
temperature would be seen as an uneven color quality
over the resulting reproduction.
VOLTAGE VARIATIONS.
­Fluctuations in the
voltage or electric current affect the color temperature
of copy lights. When the voltage to your copy lights
varies, consult an electrician. The electrician can trace
the source of fluctuation and recommend the best action
to overcome the problem.
Parabolic Reflectors
An important element of the lighting equipment for
copy work is the reflectors. Parabolic reflectors should
cause the light to be evenly distributed over the surface
area of the original and not cause hot spots. Certain types
of lights, such as reflector photoflood lamps, have
built-in reflectors. By use of the correct reflectors with
artificial light sources, exposure times can be shortened.
Daylight
Daylight can be another excellent source of
illumination for copying. When the sun is used, you
should try to use the sun during the midday hours where
a combination of daylight and skylight is present,
because of the shifting of color temperature throughout
the day. The early morning and evening hours should be
avoided when color film is used, because the lack of blue
light present. Heavy overcast skys or copying in shadow
produces a bluish cast and should be avoided or
corrected with a filter.
Filters
The use of filters was fully discussed in chapter 3.
Both correction and contrast filters, as well as special
filters, are used extensively in copy work
FILMS FOR COPYING
For copying, you can achieve the best results by
selecting the correct film for the type of copy work to
be done. Copy-type films are designed specifically to
compensate for the compression that occurs in tone
reproduction and it provides an improved highlight tonal
separation. Copy films are available only in 70mm and
sheet film formats. Although 35mm film can provide
acceptable results, you should use sheet film since it
provides higher-quality enlargements and is easier to
retouch.
Film characteristics, such as color sensitivity and
contrast, are important when you select the film to copy
a specific type of original. Film characteristics were
discussed in chapter 2.
SELECTING THE PROPER FILM
The following factors should be considered when
choosing the proper film:
The color of the original to be copied
The contrast of the original
The contrast of the film
The type of product to be produced, that is,
black-and-white or color print, duplicate
negative, color or black-and-white transparency,
and so on
Color quality of the light source
Types of film available
8-10

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