example, a white card can be used to substitute highlight areas of a distant scene. A dark or a black card can be used to substitute a shadow area, an 18-percent gray card can be used to represent middle gray, or the back or palm of your hand can be used to substitute a gray tone. When the substitution method is used, take the light meter reading from the substituted item under similar lighting conditions that exist in the scene. When the scene is in bright sunlight, the substituted object must also be in bright sunlight. Likewise, a scene in shade requires a substitute light meter reading in shade. You  can  use  each  of  the  methods  discussed previously  with  the  substitution  method.  An  18-percent gray card can be used for the integrated or averaging methods, a dark and a light card can be used for the scene brightness range method, a dark card for the darkest object method, and a light card for the brightest object method. Bracketing Method There are times when unusual lighting or subject brightness prevents you from getting an accurate light meter reading. In these cases, a good insurance policy is to bracket your exposure. To bracket, you should take one picture at the exposure indicated by the light meter, and then take two more exposures: one at one f/stop under the indicated exposure and another at one f/stop over  the  indicated  exposure. When you are in doubt about the correct exposure for  a  negative  type  of  film,  it  is  always  better  to overexpose than underexpose. Even though over- exposure produces excess densities in the negative, it still provides a useable image that can normally be corrected in the printing stage. When underexposed, if the image does not exist on the film, no corrective printing techniques can provide image detail. When shooting reversal film (slides), you should bracket in 1/2 f/stop intervals. Because the exposure latitude of slide film is limited to ± 1/2 f/stop, you should bracket in 1/2 f/stop increments, both under and over the indicated  light  meter  exposure  reading.  Color  slides  that are 1/2 f/stop underexposed have more color saturation and are more usable than ones that are 1/2 f/stop overexposed and appear “washed out” and light. TAKING LIGHT METER READINGS When taking light meter readings, you must be sure the reflected light that influences your light meter is actually from the object you want to photograph. Stray light, backlighting, large dark areas, and shadows can all cause erroneous light meter readings. When using a light meter, be sure that shadows are not cast from the light meter, camera, or yourself. When a hand-held light meter is used, the distance of the light meter to the subject  should  not  exceed  the  shortest  dimension  of  the object; for example, when taking a light meter reading of a person’s face that is approximately 9x6 inches, you should hold your light meter about 6 inches from the face of your subject when taking the meter reading. When using a light meter that is built into a camera, be sure to focus on the image before taking a light meter reading. CAUSES OF FALSE LIGHT METER READINGS There are a number of reasons why light meters give erroneous or bad readings that produce underexposed images. You can prevent these bad readings by being aware of the conditions that cause them. Light  Entering  the  Viewfinder Light entering the viewfinder and falling on the viewing screen can cause underexposure. Most TTL meters read the light falling on the viewing screen from the lens. When strong lighting is coming from behind the camera, it can influence the light meter. When an occasional  underexposed  frame  in  an  otherwise successful series occurs, the cause may be light entering the SLR viewfinder. Make a point of shielding the view- finder if you do not have a rubber eyecup. When you use a tripod, have the camera set on automatic and cap the viewfinder to prevent exposure errors. Incorrect Film Speed Setting When the majority of frames on a length of film are consistently  underexposed  or  overexposed,  the  most likely cause is you have the wrong ISO set on the film speed dial. For black-and-white film and color reversal film, it may be possible to compensate for this in developing if detected before the film is processed. Bright Subject A bright object or highlight area can affect the sensing area of a spot or center-weighted TTL meter. This results in an underexposed image. To prevent this from occurring, you should ensure the sensor is pointed directly at a midtone within the scene, and use this as the camera exposure. When you frame and compose 4-25