Sheet film
From Wikipedia, the free encyclopedia
Sheet film is large format and medium format photographic film supplied on individual sheets of acetate or polyester film base rather than rolls. Sheet film was initially supplied as an alternative to glass plates. The most popular size measures 4×5 inches; smaller and larger sizes including the gigantic 20×24 inches have been made and many are still available today.
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[edit] Using sheet film
To use sheet film, the photographer places a sheet of film, emulsion side out, into a film holder in the dark, and closes the dark slide over the loaded film. Next, the holder is inserted into a large-format camera, and the dark slide is removed from the holder. The exposure is made, the dark slide is replaced, and the film holder is removed from the camera.
[edit] Notches
Sheet films have notches cut into one short side. This makes it simple to determine which side is the emulsion, when the film is hidden from sight (in the darkroom, or inside a changing bag). When holding the sheet in "portrait" orientation (short side up), with the notches in the upper right, the emulsion side is facing the photographer. The notch patterns vary in size and layout; each type of film has its own distinct pattern, commonly referred to as a notch code, to enable film type identification.
[edit] Developing Sheet Film
Many photographers who use large-format cameras and sheet film, do their own film processing. Some more professionally-oriented photographic labs will process color negative and positive sheet film, but the "corner drug store" photolab generally can not. There are multiple methods that can be used.
[edit] Tray Processing
The simplest method for processing sheet film is using trays. The equipment, one darkroom tray per processing solution, is easily available and inexpensive compared to most of the other methods. There is also a much lower volume of solution required when using trays - only what's needed to cover the films (though most film development chemicals have minimum solution-volume-per-film-area requirements, which may require use of more solution). The films are placed into the chemical-filled trays one every few seconds, and a stack of films is formed. Agitation is performed by "shuffling" the films; the sheet on the bottom of the stack is brought to the top and pushed down into the solution. The photographer shuffles through the stack at the same rate he/she introduced the films into the processing chemical. With careful counting and practiced hands, a photographer can process as many as 10 sheets of film at one time.
Some metal multi-sheet film frames are available for handling multiple sheets as one; they require larger trays than the stacking methods, and generally preclude any stacking for risk of film damage.
The drawbacks of tray processing are that the photographer must spend the entirety of the processing time in the dark, with his/her hands in the various chemicals (some wear gloves, but they can reduce the ability to feel the individual sheets of film). Some photographers also have problems with scratching of the film's emulsion when using this method.
[edit] Tank Processing
This is also referred to as "dip and dunk" processing. The equipment requirements are greater than tray processing; a tank for each processing solution is required, along with film hangers for each sheet of film the photographer wishes to process. A film hanger is a metal frame with perforated edges which holds a single sheet of film. The films are inserted into the film hangers, and simultaneously submerged into the tank. Agitation is performed by lifting the hangers out of the tank, tilting them to one side to allow them to drain for a brief moment, resubmerging them, lifting and tilting to the other side, and resubmerging. Many photographers will bang or drop the hangers on the tank's top after the second tilt, to dislodge any air bubbles that have stuck to the film.
Tanks are also helpful for long development techniques such as "stand" development. The films are simply allowed to stand in (generally highly dilute) developer, with no agitation, for possibly hours.
The drawbacks of tank processing are the higher equipment requirements, and the fact that quite a large volume of solution is required for each step. For example, a tank for 4×5 inch film can require 64 ounces of chemistry, and a tank for 8×10 inch film can require 3 gallons. Because of this, many tanks come with floating lids, to reduce possible oxidation of such a large amount of solution. Also, despite such large chemical volumes, most tanks do not allow very many films to be processed at a single time; generally 6 or 8 is the maximum. Tank processing, like using trays, must also be performed in the dark. Some photographers report uneven development using this method.
[edit] Rotary Tube Processing
With rotary processing, films are loaded into tubes for processing. The solutions are poured or pumped into the tubes, which are turned on their sides and spun, sometimes by hand, and sometimes by a motorized base or machine. The simplest form of rotary processing is to use one tube per film; no extra reel or complex film-holding device is needed. The film is loaded, solution added, tube closed, and the tube is spun, by hand, floating in a water bath. The direction of spin is normally reversed after a couple of spins. Some rotary tubes utilize reels to hold multiple films inside the tube.
Some rotary systems use a motor to do the spinning, instead of the photographer. These systems sometimes have variable rotation speeds, and will reverse direction automatically. Systems such as these are quite convenient; the require nothing of the photographer other than changing the solution at the appropriate time. Some more complex systems can even do the chemistry management, requiring nothing but a simple programming step.
Benefits of rotary systems are even development, and very low solution requirements. In many cases, the processing may even proceed with the lights on. The photographer can also generally keep his/her hands free of chemistry, since the solutions are enclosed in the tubes. Also, since many rotary systems have or use a water bath, the bath can be temperature-controlled, resulting in very consistent results across different processing runs.
Drawbacks with a one-film-per-tube method is that processing any amount of film can take a very long time; it's difficult to keep up with more than one or two tubes at a time. A mechanized rotary system, depending on its features and capabilities, can be very expensive.
[edit] Benefits
Sheet film is, simply enough, big. Many of the larger formats can be contact printed, and for some ultra-large formats, are only contact printed. If enlargement is required, the degree of magnification is much lower for a given print size than with 35mm or 120 films. Sheet films can often be enlarged to poster, or even billboard, size with acceptably low loss of image quality. It's also possible, since the images are large, to do retouching directly on the surface of a sheet of film.
Each sheet can receive individualized processing. Since each exposure is its own sheet, it's possible to alter development, based on the content of the photographed scene, to best fit the dynamic range of the subject. Because of this, many large-format photographers are also practitioners of the Zone System.
Because of the large size and very manual single-use nature of sheet films, it's possible to use a single sheet for more than one exposure. Using a dark slide which has been cut in half, turning a standard format into a long, skinny panoramic format is simple and very cost effective. While the holder is in the camera, the photographer removes the complete dark slide and inserts the half slide, then makes an exposure on half the sheet. The half dark slide is flipped over, and the other half of the film is available for a second shot. The practice originated with photographers taking pictures of groups of banquet attendees, giving these "banquet" formats their name. 4×10, 7×17, 8×20, and 12×20 inches are the most commonly used of these formats.
[edit] Availability
Despite the advancement of digital imaging, the market for sheet film is still healthy and thriving. As of February 2006, Eastman Kodak and Fujifilm manufacture black-and-white, color negative and color transparency sheet films. Ilford, Maco (also available as Rollei), Efke, Bergger, Foma, Arista, and Forte manufacture black-and-white negative sheet films. Polaroid continues to produce instant film, both color and black-and-white, which is available in 4×5 and 8×10 inch formats.
Some 4×5 inch films are available in pre-loaded, disposable envelopes which can be conveniently loaded into a special film holder in daylight. Kodak calls their system Readyload, and Fuji's system is called Quickload. Each manufacturer makes a film holder for its system's envelopes; the Polaroid 545/545i instant film holders also take both systems' films. In addition to eliminating dust problems, these daylight-loading systems reduce the amount of gear a photographer must carry to only a single film holder. However, there are very few emulsions available as pre-loaded films, and only in 4×5 inch format. The envelopes also cost significantly more per exposure than the corresponding sheet film.
