Figure 13-1.–Camera Sizes and Lens F-1 Lengths 8mm 16mm 35mm Normal 12mm 25mm 50mm Wide Angle Telephoto 6 to 9mm 25mm  and  above 13 to 17mm 38mm  and  above 35mm  or  less 100mm and above EXPOSURE CALCULATION NOTE: 360 is a constant factor (number of degrees AND CONTROL in a circle). Exposure meters for measuring incident light can be used directly to help determine lighting ratios. A gray card  is  used  to  get  an  accurate  exposure  reading whenever reflected light meter readings are taken. Incident light exposure meters are very useful for motion pictures because they can be used at a scene to calculate  exposure  before  the  subject  arrives.  They  also can be carried throughout the scene, thereby indicating uneven lighting or “hot spots,” thus indicating whether the  lighting  should  be  altered. With a motion-picture camera, the final exposure adjustment is usually made only with the aperture because fps rate of the camera determines the shutter speed. The goal of exposure control for motion pictures is to produce consistent and uniform image densities and tones from one scene to the next. Accurate and correct exposure control can be achieved only through the proper use of a good exposure meter. The exposure time for a movie camera is a result of the rate at which the camera is operated (usually 24 fps) and the shutter degree opening (the degree of the open segment of the shutter). The shutter degree opening for a particular camera is provided by the camera manufacturer.  Given  the  shutter  degree  opening,  you can determine exposure time by use of the following formula: Shutter Degree Opening 360  x  fps =  Exposure Time in Seconds For example, suppose you have a camera with a shutter degree opening of 175 degrees and you intend to be filming at the standard rate of 24 fps. Determine the shutter  speed  as  follows: Shutter  Degree  Opening 175 175 1 360  x  fps = 360 x 24⁼ 8640⁼ 49 or 1/50 second The  information  on  exposure  provided  in  chapter  4 applies equally well to motion-picture photography as it does  to  still  photography. Neutral density filters (ND) are often used in motion-picture work to help control exposure because of the limited f/stop and shutter speed combinations available on motion-picture cameras. When you are shooting a movie, the fps and the shutter degree opening are fixed. You may not be able to open up the aperture to get the correct exposure control and depth of field; therefore, you would use an ND filter to reduce the amount of light reaching the film. Remember, because of the fps rate, you are restricted to a given shutter speed, and  stopping  the  lens  down  would  destroy  your depth-of-field   effect. MOTION  VIDEO Videotape   recording   has   basically   replaced motion-picture film making. Motion video has a number of  advantages  compared  to  motion-picture  coverage. Some of these advantages are as follows: A videotape camera can record black and white as well as color. No time-consuming film processing is required and  recordings  can  be  played  back  immediately. When necessary videotape may be partially or completely erased and used again for several more recordings. It can be played back numerous times  and  may  be  stored  indefinitely. Videotape is edited or assembled more quickly than film. Videotapes are duplicated and distributed easily to  other  Navy  activities. A video camera is optically similar to a movie camera, except it does not use film. Considering the 13-3