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Color Analyzers

After introducing the Chromega colorhead in 1959, it was logical that Omega would eventually distribute color analyzers as well.  Beginning with the Simtron in 1965, they marketed a series of analyzers in different price ranges into the 1980s.  These units are often available on the used equipment market.

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SCA-400 Automatic Digital Color Analyzer/Timer

SCA-300 Digital Color Analyzer

SCA-100 Color Analyzer and Exposure Meter

Chromegatron Pro-Lab Color Analyzer
Chromegatron Pro-Lab

Simtron II Color Analyzer
Simtron II

Chromegacolor Solid State Color and Exposure Analyzer

Super Chromegatron II Solid State Color and Exposure Analyzer 
Super Chromegatron II

Super Chromegatron Solid Sate Color and Exposure Analyzer
Super Chromegatron

Simtron Color Print Analyzer


Analyzer Readings

Color 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  CdS cells have, for the most part, been superceded by silicon blue cells.

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 available.

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.


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