Table 4-2.–Action Stopping Shutter Speeds for Normal-Focal-Length LensesSpeed MPHType of ActionDistanceDirection of Action51025100Slow walk, working with thehandsFast walk/ work,slow-moving vehiclesRunning, sports, very activepeople, vehicles moving at amoderate speedVery fast-moving vehiclesand aircraftTable 4-3.–Equivalent ExposuresEXPOSURE CONTROLShutter Speed1/20001/10001/5001/2501/1251/601/301/15121/5001/2501/125251/2501/1251/60501/1251/601/301001/601/301/15121/10001/5001/250251/5001/2501/125501/2501/1251/601001/1251/601/301225501001/20001/10001/5001/10001/5001/2501/5001/2501/1251/2501/1251/6025501002001/20001/10001/5001/20001/10001/10001/5001/5001/2501/2501/125f/stopf/4f/5.6f/8f/11f/16f/22f/32f/64the light level may be so low that you have to use a slowshutter speed and the largest f/stop to get the properexposure. After determining the correct exposure, youcan decide how to present the subject. Remember, depthof field can be used to emphasize your subject, andshutter speed affects subject blur.Across Fieldof ViewDiagonallyStraightToward orAwayThe term exposure in photography means theamount of light that reaches the film or otherlight-sensitive material. The mathematical formula forexposure is the product of light intensity and the amountof time that the light acts on a light-sensitive material.There are two ways a formula is presented inphotographic publications. They are as follows:E = I x TandH = E x TWhere:E or H = Exposure (lux-seconds or meter-candleseconds)I or E = Intensity or illuminance (lux or metercandles)T = Time (seconds)Both of these formulas represent exposure. The secondformula is presented in the more current publications.4-17