Side  Lighting.–As the camera is moved in an arc away from frontlighting, less light is reflected from the subject into the lens. Whenever the light source has a 90-degree relationship with the camera, the incident light on the subject is called side lighting. In side lighting situations, part of the subject is in shadow. Photographs of side-lighted scenes usually require two times (one f/stop) more exposure than frontlighted subjects when you want detail in the shadows. Backlighting.–When the light source is directly behind the subject and aimed toward the camera, it is called backlighting. In back-lighted situations, the subject is in shadow and the light reflected from the subject toward the camera is decreased greatly. A silhouette effect (no shadow detail) of a back-lighted scene is produced by closing down one f/stop from the basic exposure. If shadow detail is desired, an increase of four times (two f/stops) from the basic exposure is required. Reflection   Properties Otherwise the intensity and direction of light falling on the subject, the texture of the surface, and the colors and shades of the scene also have an effect on film exposure. SURFACE TEXTURE.–Smooth, glossy surfaces scatter or diffuse reflected light very little; therefore, these objects reflect a large percentage of light to the lens. Rough surfaces greatly scatter and diffuse light. Less light from rough surfaces is reflected to the lens. COLORS AND SHADES.–Not all light that falls on the surface of a subject is reflected. A brilliant white object reflects a high percentage of incident light, and a black object reflects very little of the light. Between these two extremes are the numerous tones of gray and colors of various hues and brightnesses. Each colored or gray object in a scene reflects a specific amount of light. A scene that consists primarily of light-colored or light-toned  objects  usually  requires  an  exposure compensation to decrease the exposure as compared to the basic exposure for an average scene. A scene that consists  primarily  of  dark-colored  or  dark-toned  objects usually requires an exposure compensation to provide more exposure as compared to the basic exposure for an average scene. The primary reason light scenes and dark scenes  require  less  exposure  and  more  exposure, respectively, as compared to the average scene, is to maintain detail in the highlight of the light scenes and detail in the shadow areas of the dark scenes. The color quality of a light source also has an effect on the amount of light reflected from an object; for example, a blue object does not reflect as much light when illuminated with a red light source, as compared to the same object being illuminated with a blue light source. This difference in reflectance is caused by the blue object absorbing the reddish light and reflecting the bluish light. Any man-made light is an artificial light source. This light may be a tungsten lamp, a fluorescent lamp, a mercury-vapor lamp, and so on. The same factors that affect exposures for daylight apply to artificial light as well. Artificial light has some advantages. Distance, direction, and color temperature can be controlled using these  light  sources. Bellows  Extension When copy cameras or view cameras are used, many subjects are photographed at very close distances. When you are photographing at these close distances, it is not uncommon for the bellows of these cameras to extend beyond one focal length. The farther the bellows are extended, the larger the image size produced at the film plane. When a 1:1 subject to image ratio (on the film plane) is needed, the bellows are extended to two times the focal length of the lens; for example, when a 6-inch lens is used to produce a 1:1 ratio, the bellows are extended to 12 inches. The distance the bellows are extended  is  determined  by  measuring  the  distance  from the optical center of the lens to the film plane. When the bellows are extended beyond one focal length, an exposure compensation is needed. Because light must travel a greater distance, some of the intensity is lost. This loss of light intensity must be compensated for  by  opening  up  the  aperture  or  increasing  the exposure time. There are two formulas used to adjust the exposure  when  the  bellows  are  extended. Generally,  the  exposure  time  is  extended  to compensate  for  bellows  extension,  because  view cameras and copy cameras are mounted securely and the critical aperture is used to produce the sharpest image. To adjust the exposure time, use the following formula: BE² FL x  T = NEW EXPOSURE TIME Where: BE = Bellows extension FL = Lens focal length T = Indicated exposure time 4-20