There are a number of special effects that fall in the category of unconventional tone reproduction, some of which involve after treatment of conventional photogrpahic images.
Bas relief- This is a technique whereby a positive image is made of the original negative by contact printing. The negative and positive are then superimposed. The sandwiched pair is then set slightly out of register and printed. The exact pictorial effect varies depending on the density of the positive record and the density to which the larger areas of the image are printed. Usually, the broader areas appear devoid of large density variations but they retain their identity. The edges of these areas, because they gain or lose relative density as a result of the superimposition process, impart a "shadowing" effect in the direction that the two records were displaced. While this is the most common way to do bas-relief, variations have been produced where the two records are of slightly different sizes giving yet another variation on the same general theme.
Line derivation- This is a technique closely allied to isodensity and it is also created by the combination of a high contrast negative with a high contrast positive which are superimposed so that no light is able to pass through the combination. In this case, however, the two superimposed records are then slightly separated. The combination may be placed on a turntable and while a light is shining from the side, the sandwich is turned in such a manner that light is able to pass past the edges of the combined pair and expose the film or paper underneath. This results in a line pattern defining the edge or join line between the positive and negative records. Fine detail tends to be lost however.
Solarization- Considered synonimous with the Sabbatier effect. In the strictest sense solarization is an exposure effect associated with gross overexposure that causes image reversal. This effect would primarily apparent in the highlights of the subject appearing in negative form on a black and white print, such as the image of the sun being reproduced black rather than white.
Sabattier effect- The Sabattier effect is an effect that is a result of further overall exposure or fogging of the film or paper, beyond the exposure due to the first or image forming exposure. The Sabbatier effect is induced by exposing the sensitized material to light after the development step has progressed beyond the initial stages. The effect is that there appears to be a reversed or negative image in combination with the normal, positive, image that would be formed during the normal printing process.
Posterization- This is a special effect that is the result of the sequential printing of a number of high contrast copies of an original but where each copy is of different overall density. These copies are typically printed in registration and the final density of the reproduction at any given area on the print is a result of the contributions of the partial exposure that resulted from exposure to each of the several partial "masks" that were created from the original. Posterization as well as many other special effects processes can be done in B&W as well as color. In B&W the subject tones are broken down into a series of stepped densities while when this process is carried out in color, original subject tones can be made to achieve almost any desired color.
Isodensity- Although a rather seldom seen special effect, this method relies on counteracting negative and positive emulsions coated on a single support. A film of this type is manufactured by AGFA. The effect is that areas of the subject that produce more or less exposure at the emulsion than a critical level (adjustable by the choice of overall exposure) are reproduced as dense areas. The critical exposure level is reproduced as clear film base. The clear lines that result are then interpreted as lines of equal photographic effect or isodensity.
A similar effect can be achieved by high contrast positive and negative images keyed about a particular density of an original. Combining these will reveal a low density region that follows areas of the originals that had the same density.
The process is basically a variation of the bas-relief and the line derivation techique described above. The only difference between the processes is that in this technique the high contrast negative and positive are created simultaneously and are in perfect registration.
LIGHTING EFFECTS
The creative use of filters and lighting devices introduces yet another special effect area for the creative photographer. Electronic flashes have been a long standing tool in the special effects arsenal used by photographers not only to create frozen images of fast moving events but also to convey the opposite, an idea of the sense of the motion of the subject. Their application for this purpose is described under the heading of stroboscopy.
Color balancing- A not too obvious special effect involves balancing light sources of different color characteristics included in the same scene so that they will appear to be matched in color quality to the film.
One of the most common applications of this process involves the balancing of fluorescent illumination in a scene with daylight type illumination provided by an electronic flash. The flash is covered by a greenish filter to convert its color quality to that of the fluorescent tubes and then a magenta or reddish filter is placed over the camera lens to simultaneously bring both of them back to daylight quality to match the film with which the photograph is made. The filter on the flash and the filter on the camera need to be complementary in color and strength to each other.
If fluorescent tubes need to be included in an indoor scene that also includes daylight another technique that can be used is that of split exposure if the subject is a static one. The photograph of the outdoor portions of the scene is first made while all fluorescent lights are turned off. The camera is held immobile until nighttime when the next exposure is made by only fluorescent or by a combination of fluorescent modified flash and color correcting filter placed on the camera lens.
Multi-color exposure- Interesting effects can be produced by using filters of complementary color to dramatically alter the color of a background while keeping the color balance of a foreground subject quite normal if the subject can be lit by one light source while the background is lit by a second source. For example, placing a color filter on a flash that illuminates the subject that is complementary in color to the one placed over the camera lens and which will be used to tint the background a particular color will counteract the effect of the filter tinting the background resulting in basically neutral rendition of the flash illuminated subject.
Normally one would not intentionally introduce unnatural color casts in a photograph. On the other hand the use of filtered light sources illuminating the subject from different locations is another area of creative application of lighting as a special effects tool.
Tailflash photography- Typically the "X" synchronization system built into most cameras and shutters causes electronic flashes to be triggered immediately upon a given shutter achieving maximum opening. The pictorial effect of this convention is that when combining existing illumination with electronic flash illumination while photographic a moving subject this results in the subject appearing to be moving backwards. This is because the "blur" exposure due to existing illumination happens after the electronic flash produces its action stopping flash exposure and thus the blur is impressed on the film after the sharp record.
To place the flash exposure at the end of the tungsten exposure some modern cameras have a provision built in that allows the photographer to chose between triggering the flash at the beginning or at the end of an exposure. With 35mm cameras this is often referred to as second curtain synchronization. In cameras or shutters that do not have this provision built in, accessory devices are available to provide a similar function. Since diaphragm shutters do not have curtains, the process of setting off an electronic flash at the end of an exposure may better be defined as trailing flash synchronization or simply tailflash synchronization.
Stroboscopy- The use of repetitive flashes to generate images that convey a sense of motion of the subject is achieved in several ways. The most common technique places a subject against a very dark, nonreflecting background while it is illuminated by the flashing stroboscope. As the subject begins to perform the desired motion the shutter is opened. At the completion of the motion the shutter is closed. During the interval that the shutter was opened several images of the subject are recorded. Their number is a function of the frequency of the flash and the exposure time. Areas of the subject that move to new positions on the film are easily seen in their respective locations. Those parts of the subject that remain relatively stationary suffer from overexposure and generally blend into a detailless mass. Generally this means that a particular action can only be followed over a very limited time period because of multiple exposures on the film tending to mask previously recorded images.
Although the above effect is possibly desirable, photographers overcome the limitation imposed by subjects performing an action in a stationary location, by either introducing artificial translational movement in the subject or the camera, by panning the camera or introducing motion in the film stock. This latter movement is generally accomplished by rewinding the film into its supply cassette after preparing the camera by first advancing the film into the camera's take-up chamber without exposing it. The shutter of the camera is held open while the film is rewound. With each flash of the stroboscope not only is the subject in a slightly different position but the image is recorded slightly off to one side of the one recorded with the previous flash. This technique allows the recording of a subject over an extended period of time.
See also: Electronic still photography, motion picture, video.
Addendum:
In a manner of speaking focal plane shutters are sequential exposure devices since the film is uncovered and covered in a sequential manner by the roller blind or curtains racing from one side of the aperture gate to the other. The exposure time is simple the time that elapses from the uncovering of a point on the film to the covering of the same point by the trailing curtain. The effect of the moving curtain's edge on the final appearance of the record is a function of the rate of movement of the image with respect to the rate of motion of the curtain edge during the interval that the curtain travels over the image of the subject. If the image is stationary with respect to the film then it does not matter that a focal plane shutter was used top make the exposure. If the image moves, however, then distortion will become apparent. This distortion can be called a special effect and it can be best exploited by slowing down the FP shutter mechanism or attaching an auxiliary FP shutter to a standard camera.
