One important consideration when selecting film-one too often overlooked-is the processing requirements for a given film and the printing needs for the whole production. One way to better appreciate the sophisticated technology that turns your exposed camera film into good projection film is to understand the processes and equipment in the modern film laboratory. In this section, we will describe the operations and equipment involved in processing and printing your film.

Processing Equipment
The modern motion-picture laboratory uses the continuous processor, a machine that provides the most efficient way of handling long lengths of film. Other kinds of equipment can be built or purchased for development of small amounts of black-and-white footage, but the continuous processor meets the quantity and quality demands of professional processing. In essence, the continuous processor moves film through the appropriate sequences of developers, fixers (or stop baths), washes, and dryer at a carefully controlled speed. The processor also controls solution temperature and agitation to produce optimum results for the particldar kind of film being processed.

Construction of Containers
Glass, hard rubber, polyethylene, 316 stainless steel, and titanium are the materials most commonly used in the construction of containers for mixing, storing, and using photographic solutions.

Not all metals are suitable. Tin, copper, and their alloys may cause serious chemical fog or rapid oxidation when used with developers. Do not use aluminum, zinc, or galvanized iron with either developers or fixing baths.

Transport Design
The film follows a helical path by moving on partially or totally submerged banks of rollers through the various solutions (Figure 57). Squeegees (Figure 58) or wipers located between the different tanks remove most of the liquid from the film surface. The most common method of moving film through a processor is by friction between the rotating spools and the base side of the film. The other major method is by sprockets incorporated on the spools which engage the film perforations.

Helical path of film through a single rack and tank assembly Figure 57	This type of wiper-blade squeegee assembly is used on many processors. Figure 58
	Roller undercut in image area.
	Roller with soft-touch tire installed. Figure 59

The film path through the processor wet sections permits only the base side of the film to contact the rollers. In this way, the emulsion is protected from possible physical damage that might occur if the soft, wet emulsion came in contact with the plastic spool surfaces. However, in the dry sections (feed-on and take-off) of some processing machines, there may be emulsion- side rollers. These are usually under cut in the image area and are designed to contact only the edges or perforation area of the film. Some rollers have ridges that touch only edges of the film, or the rollers can be flat and covered with soft-touch tires for uniform film support across the roller width and to prevent scratching of the support in the image area. See Figure 59.

Access Time
Two of the most widely discussed and perhaps the most misunderstood items relating to any processor are speed and access time. Speed refers to the time required for a specific point on a film to travel a specific distance and is measured in feet or meters per minute. Access time refers to the time it takes a particular length of film to be completely processed. Regardless of machine transport speed, which can range from 15 to hundreds of feet per minute, film cannot be processed faster than the total of the times required in each solution. For example, when a machine running Process VNF-1 is loaded and processing film, it will be 15 minutes 15 seconds before the first foot of film enters the drying cabinet no matter what the speed of the machine. However, the time for completing various lengths of film once the process times are met is in direct relation to the machine speed. If the machine speed is 15 fpm, then a 15-foot-long film will take 14 minutes 15 seconds plus 1 minute to complete the process. With a 150-foot roll, access time will be 14 minutes 15 seconds plus 10 minutes.

Time and Temperature
In black-and-white processing, time and temperature may vary widely among motion picture laboratories. Each laboratory selects the appropriate development times and temperatures for the films being processed in a particular machine and with a particular formula. This is accomplished by producing a time-gamma curve, as discussed in an earlier chapter. (Some modifications in the control-gamma aim may be necessary depending upon the type of sensitometer or densitometer being used.)

For color films, specified temperature tolerances, particularly those for the developers, are critical. Developer tolerances of +/- 0.3^oC (+/- 0.5^oF) are typical. Appreciable deviation from these limits results in speed and color- balance changes. Many commercial motion picture laboratories have found it feasible and profitable, in terms of consistent quality, to control the developer temperature to within +/- 0.15^oC (+/- 0.25^oF), or even less. Process ECN-2 requires that the developer temperature be held within +/- 0.1^oC (+/- 0.2^oF).

Controlling processing time is also more critical with color films than with black-and-white films because any changes that occur in color emulsions may not be equal in all layers. Improper color reproduction can result from speed shifts, contrast changes, increased fog, etc., in any of the layers. Therefore, a good lab adheres closely to the exact processing specifications for the particular equipment and materials.

Agitation
If exposed photographic materials are placed in a developer and allowed to develop without movement, the action slows down because the developing chemicals in contact with the film surface become exhausted. If the film or the solution is agitated, however, fresh solution is continually brought to the emulsion surface, and the development continues. An equally important effect of agitation is prevention of uneven development that may result in mottle, a nonuniform density in the print that makes it look blotchy. If there is no agitation, the exhausted solution, loaded with development by- products, may flow slowly across the emulsion from dense areas to less dense areas and produce uneven streaks. Agitation keeps the solution uniform throughout and avoids uneven development. In color processing, proper agitation is especially critical during the initial development step. The recommended agitation techniques will vary, depending upon the process and equipment being used. The film movement, as it passes through the developer solution is not always sufficient to create adequate agitation.

Mechanical Specifications
If film is to be processed satisfactorily as it moves through the machine, it must be immersed in solutions of the correct temperature for the proper length of time. In addition, processing solutions must be adequately replenished and filtered, and sufficiendy agitated. These requirements are commonly called the mechanical specifications.

The only valid processing change-made for the purpose of force processing (for more camera speed under low-light conditions)-involves increasing the developer (camera negative) or first developer (reversal camera film) time and/or temperature.

The time that film is immersed in a particular solution depends upon the length of the film path in each tank and the machine speed. Generally, time is fixed by the number of rollers per rack and the number of racks threaded in a tank. Usually, individual rack times can be changed by rethreading the rack or using a rack equipped with an adjustable lower-shaft assembly.

Temperatures on most processors are controlled automatically, often to within +/- 0.1^oC but can usually be adjusted manually to accommodate any desired temperature changes. The laboratory also keeps a highly accurate thermometer available to double check the processor temperature gauges.

Process Control
The degree of development in a negative-positive process or first development in a reversal process is the most important factor in determining the final image quality. Careful control is critical at this point. Development is affected by the temperatures and chemical composition of the developer (or first developer), the time of contact between the film and the solution, and the degree of agitation. The other processing steps are also affected by the same factors.

When all is well with the process, the output from the continuous processor will be good pictures. While these pictures can be evaluated subjectively by simply looking at them, the most accurate evaluation is an objective measurement Sensitometric control strip density values, when plotted in graphic form, give an operator that objective information about the condition of the process. These measurements are made before, during, and after a processing run for maximum control of quality.

The operator also checks the physical operation of the machine periodically to ensure good results. A good lab observes the following practices in the physical control of a process:

• Use of correct processing temperatures, which are checked often. Thermometers and temperature-controlling devices are calibrated periodically to insure that the instruments are operating properly. The temperatures of all solutions are kept within specification to minimize dimensional changes in the emulsion.
• Use of recommended processing times. Machine speed is checked by carefully measuring the time it takes for a given length of film to pass a specific point. Knowing it is possible to use an incorrect processing time when a machine uses different thread-ups for different film stocks, the careful laboratory checks the solution times every time there is a threading change. Consider that, for black-and-white negative or positive process, one might run up to seven films having nine possible development times through Developer D-96 in the course of a few hours.
• Use of the recommended replenishment rates. Accurate replenishment increases the useful life of solutions to a great extent by replacing ingredients that are depleted and maintains the process at a constant, efficient level. To prevent serious out-of-control situations and chemical waste, laboratories routinely check the accuracy of their replenisher delivery systems.
• An accurate daily record is kept of conditions affecting the process, including developer temperature, amount of film processed, volume of replenisher added, and identification numbers of control stops processed at particular times.