speed dial, the top part of the fraction (numerator) is not indicated; for example, the shutter speeds 1/60, 1/125, 1/250, and so forth, are indicated as 60, 125, and 250. When a camera with a focal-plane shutter is used with an electronic flash, a predetermined shutter speed must be set. At this speed the shutter and flash unit are said to be in synchronization. When the flash and shutter are synchronized, the shutter opening is wide open at the same  instant  the  flash  fires.  Usually,  the  slowest  shutter speed that syncs with a flash unit is indicated in red or another off color or a lightning bolt symbol on the shutter  speed  dial. Function The shutter serves two functions: controlling the duration  of  the  exposure  and  controlling  subject movement. These two functions are entirely separate and distinct. You must determine the shutter speed required for each condition. After determining the shutter speed, you select the f/stop that provides the correct  exposure  for  the  film  speed  and  lighting conditions. Normally, the duration of exposure is short enough to prevent image blurring. You can always set the shutter speed faster than the speed required to stop image motion, but it should not be longer if you want the image to be sharp; for example, when a shutter speed of 1/125 is sufficient to stop subject motion, you can set the shutter speed to 1/250 or faster, but not at 1/60 if you want to stop the motion and produce a sharp image. Each time you change the shutter speed, the diaphragm is adjusted  to  produce  a  properly  exposed  image. The  correct  sequence  in  determining  the  diaphragm and shutter to produce a properly exposed negative is as follows: 1. Compose and focus the image. 2. Stop down or open up the diaphragm until the desired  depth  of  field  is  achieved. 3. Select the shutter speed that will produce a proper exposure when combined with your aperture  setting. 4. Determine whether the shutter speed is fast enough  to  prevent  image  blurring. 5. If the selected shutter speed is too slow, reset it to a faster speed and open up the aperture accordingly. When   you   increase   the   shutter   speed,   you compromise  and  loose  depth  of  field.  Sometimes  this  is the only way to produce a useable image. If you cannot sacrifice  some  depth  of  field,  there  are  several alternative you can use: select a faster film, increase the camera-to-subject  distance,  select  a  shorter  focal  length lens, or change the camera angle, so the relative motion of  the  subject  to  the  camera  is  decreased. Selecting the Shutter Speed Knowing  what  shutter  speed  produces  the  right effect  for  each  picture  is  a  skill  you,  as  a  Navy Photographer’s Mate, must acquire. Your pictures may easily be spoiled by movement of either the camera or the subject. In some instances, this movement can actually  improve  your  photographs. Novice photographers often find it hard to believe anything can happen during the brief instant the camera shutter is open. This is not true; images can be blurred when a shutter speed as fast as 1/250 of a second is used; for example, when the camera or subject moves during the fraction of a second the shutter is open, the image may be recorded on the film as a blur. Blurring caused by  camera  movement  is  noticeable  in  all  images  within the  photograph.  When  blurring  is  caused  by  subject movement only, the background or some other part of the scene will be sharp, and the subject blurred. Camera movement blur can be corrected by supporting the camera properly or by using a faster shutter speed. Subject image movement can be reduced by using either a faster shutter speed or by panning the subject. As explained previously, when a faster shutter speed is used, a wider aperture is required to produce correct exposure. For this reason you should know what minimum shutter speed is required to stop or freeze different actions. You must take into account conditions that exist when taking photographs. Strong winds, vibrations, or a ship rolling from side to side must be considered. There is a general rule you must follow for determining  shutter  speed  when  handholding  a  camera. The  slowest  shutter  speed  recommended  to  prevent camera movement blur is to set the shutter speed so it matches the focal length of the lens. When a shutter speed does not exist for the focal length of the lens, select  the  next  highest  shutter  speed;  for  example,  1/30 second for a 25mm lens, 1/50 second for a 50mm lens, 1/125 second for a 100mm lens, 1/250 second for a 200mm lens, and so forth. When a subject is in motion during exposure, the image on the film also moves. Even though the duration of exposure may only be 1/1000 of a second, the image moves a small fraction of an inch during this time. The problem you encounter is how much image movement 4-14