select a wider aperture to control depth of field, start by setting your main flash at one-half or one-fourth power and  adjust  your  fill  flash  appropriately. Adjusting  lighting  ratios  by  flash-to-subject- distance is another method to control lighting ratios. An easy way to calculate footage for a 3:1 ratio with two lights of equal intensity is to think of the full f/stops (2, 2.8, 4, 5.6, 8, 11, 16, 22, etc.) as distances in feet. Place the main light at the desired distance closest to one of the  "f/stops,"   and place the fill light at the distance indicated by the next larger number; that is, 5.6 feet and 8 feet or 16 feet and 22 feet, and so on. Another easy method to control the lighting ratios using an automatic electronic flash is to use the flash unit in the automatic mode. When set in the automatic mode, the flash-to-subject distance is not supercritical, and there is some leeway as long as the flash units are within  their  operating  range. To obtain a 2:1 lighting ratio, you simply have both flash units set at the same automatic setting and at approximately the same distance from the subject. For a 3:1 lighting ratio, use the same automatic setting and approximately the same flash-to-subject distances, but set the fill flash at twice the film speed as the film being used (main flash setting). For a 5:1 or even higher lighting ratio, use the same automatic setting and approximately  the  same  flash-to-subject  distance  and set the fill flash at four times more than that of the main flash, and so on. Any lighting ratio can be obtained when using an automatic flash unit. By controlling the power output intensity,  adjusting  the  film  speed  setting,  changing  the main and fill flash distances, or a combination of the three, you can manipulate the lighting ratio easily to any ratio. As with any stage of photography, practice and testing  with  your  camera  and  flash  combinations  in various  situations  produces  the  best  results. SYNCHRO-SUNLIGHT Bright  sunlight,  used  as  the  only  means  of illumination  for  an  exposure,  can  produce  deep objectional shadows on a subject. When a flash unit is used as a fill-in source of illumination, it reduces these shadows and is known as synchro-sunlight photography. Improperly   handled,   the   synchro-sunlight technique  can  produce  an  effect  that  makes  the photograph appear as if taken at night with a single flash. This effect occurs when the flash illumination is more intense  than  the  sunlight. The first step for proper exposure with synchro- sunlight is to calculate the correct exposure for daylight, and set the shutter speed and f/stop as though a flash is not being used; however, keep in mind when using a focal-plane   shutter,   the   shutter   speed   must   be synchronized with the electronic flash unit. Avoid using a fast film in bright sunlight when using a camera equipped with a focal-plane shutter. In this case, you are limited only to your aperture to control the exposure of the film, because your shutter speed is nonadjustable. A leaf shutter has an advantage over a focal-plane shutter. When a leaf shutter is used, it provides more control over depth of field since the shutter synchronizes at all shutter speeds. When you are using an automatic flash, the same principles  apply  for  synchro-sun  that  were  explained  in the section for lighting ratio. The sun is used as the main light, and your camera settings are determined directly from your light meter. The easiest method is to set the film speed (ISO) on your flash unit to twice the film speed being used for a 3:1 lighting ratio and four times the film speed being used for a 5:1 ratio. A fraction of the manual power output can also be used to achieve the desired  lighting  ratio. Remember  to  compensate  your  exposure  by opening up two f/stops for a backlit subject and one f/stop for a subject that is sidelighted when taking your light   meter   reading   from   a   distance.   For   color photography,  you  should  normally  use  a  2:1  or  3:1 lighting  ratio.  For  black-and-white  photography,  a  ratio of 3:1 to 5:1 is acceptable. MULTIPLE-FLASH   UNITS Multiple flash is the use of two or more flash units fired in synchronization with the camera shutter. The flash units can be auxiliary flash units, connected to the camera by extension cords, or they can be slave flash units. Slave units usually have self-contained power sources and are fired with a photoelectric cell when light from a master flash unit strikes the cell of the slave unit. With multiple flash, exposure calculations are based on the distance between the subject and the flash unit that produces the most intense illumination to the subject; therefore, you can have numerous auxiliary flash units or slaves for a scene and only calculate your exposure from the mainlight source. All other flash units should be equidistant or at a greater distance from the subject as compared to the flash unit on which the exposure  is  based. 5-35