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.
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
and burn out.
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.
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.
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.
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.
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, are used extensively in copy work
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
black-and-white or color print, duplicate
negative, color or black-and-white transparency,
and so on
Basic Photography Course