analyzers are not recommended for everyone. Experienced darkroom
workers often develop such an accurate eye, and know their processes
so well, that they don't require an analyzer in order to get the
color balance and exposure close to perfect. At the other end of
the spectrum, hobbyists who do infrequent printing and purchase
supplies in small quantities would spend so much time programming
an analyzer as to make it unproductive. However, for those people
who do sufficient volumes of prints, but have not yet developed a
skillful eye for filtration, a color analyzer can be a valuable time
and money saving tool. Some features of analyzers use terminology
which may not be familiar. Below we explain some of the terms you
may encounter when comparing these units.
CdS cell - cadmium sulphide
cells are light reading cells that replaced selenium cells in
photographic light meters. Their advantages are that they have a
spectral response similar to the human eye and are small and
inexpensive. Their chief disadvantage is that they have a "memory",
so that if a cell is taken from bright light to low light, the
readings will not be accurate for some time. Even under normal
circumstances, the user must wait for readings to stabilize. CdS
cells have, for the most part, been superceded by silicon blue
Color Channels - A color
analyzer must measure each of the subtractive colors in order to
provide the user with full filtration correction. In most
analyzers, these measurements are taken by the same cell using a
different filter for each reading. Therefore, the unit requires
separate adjustment channels for Cyan, Magenta, Yellow and Exposure.
Cosine correction - When a
probe is centered directly under the enlarging lens, the light
striking the probe is at a 90° angle to the surface of the cell. As
the probe is moved away from this axis, the light increasingly falls
on the probe aperture at an angle, which affects the accuracy of the
reading. To compensate for this effect, many of the spot-reading
probes have an adjustment that allows the surface of the probe to be
tilted towards the enlarging lens so that the light being measured
is again at right angles to the cell.
Electrostop™ - this feature
allows the simultaneous sensitivity adjustment of all three color
channels without affecting the exposure channel. Since most
printers prefer to always use the optimum f/stop of the lens, this
allows the meter to be nulled without adjusting the lens aperture.
Fiber optics - In order to
provide a compact probe and protect the fragile photomultiplier
tube, many analyzers utilize bundled glass fibers as a "light pipe"
to transfer the light to the tube housed in the analyzer body.
However, with careless handling and heavy use, the individual
optical fibers can break, reducing the sensitivity and eventually
requiring replacement of the cable.
Integrated reading - using a
special lens or diffuser, the image is blended so that the analyzer
measures the resulting "average" color of the entire negative.
Integrated readings are often preferred for landscapes and general
photography where there is no single, consistent reference color
Light shock protection - since
color analyzers must be sensitive to low light levels, one problem
that can occur is "light shock," as when someone turns the room
lights on when the analyzer is still on. Some older units could be
damaged by this, but in most cases, it meant that the operator
merely had to wait for the photocell to lose its "memory" of the
bright light level. Virtually all modern analyzers include
circuitry to handle this overload situation.
Null meter - is simply a meter
which will display values greater or less than zero. When
programming the analyzer with the values used to obtain the
reference print, the analyzer controls are adjusted so that the
meter reads "0" on each color channel. The analyzer retains these
settings, and when later analyzing an unknown negative, the
filtration on the enlarger is adjusted so that the meter is at "0",
or "nulled," for each channel.
Photomultiplier tube - is a
specialized vacuum tube used as a light sensitive device in some
color analyzers. The photomultiplier tube provides the greatest
sensitivity and fastest response time. However, the tubes are
expensive, relatively large and vulnerable to physical damage.
Program channels - typically,
a user will require multiple programs to accommodate all the
variables that may be encountered, such as different types of paper
and subjects. For example, many users have programs for skin tones,
18% grey, integrated readings, pure white, as well as different
paper emulsions. On most analyzers the values for each must be
recorded and the analyzer manually reprogrammed when switching
between them. However, some analyzers have have built-in channels
or accessory modules for storing multiple programs, saving the user
time when switching programs.
Reference print - until it is
programmed by the user, a color analyzer is useless. In order to
program the analyzer, the user must produce a perfect print to be
used as reference. The filtration and exposure values used to
produce that print are then used to program the analyzer. The
reference print must be made from a properly exposed negative shot
on the same film that will be printed in future, and printed on the
on the same paper emulsion and processed with the same chemistry
that will be used. Any change in film, paper, or chemistry, or even
changing the enlarger lamp may require a new reference print and
reprogramming of the analyzer.
Sensitivity control - the
sensitivity of the light sensing devices used in color analyzers is
far greater than the analyzer is able to display at one time, so
when programming the analyzer from the reference print, you set a
default display range. Should light values fall outside of the
pre-programmed range, analyzers provide an adjustment allowing the
user to shift the range of the display. Generally, changing the
sensitivity will require production of a new reference print for
that range of light values. However, on those Omega analyzers
incorporating an Electrostop™, sensitivity can be adjusted without
the need to reprogram.
Silicon blue cell - these
cells are light sensitive cells closely related to CdS cells. By
comparison, they are more sensitive and have a much faster response
time with no "memory" problems.
Spot reading - for photographs
where there is a consistent reference color, a spot reading will be
more accurate from picture to picture than an integrated reading.
Therefore, spot reading meters are preferred for pictures with
people where skin tones tend to be the most critical areas. In
situations without a consistent reference color, photographers will
often include an 18% grey card and use this as their spot reference.
Subject failure - with
integrated readings, the assumption is made that the color from most
negatives, when blended, will average out to be roughly the same.
Subject failure occurs when the photograph contains a predominate
color, such as a shot of a bowl of strawberries against a pink
background. An integrated reading will not produce a satisfactory
result from negatives with subject failure.