Figure 2-5. Guide number versus film speed for Type 1531 intensity settings

by an external signal (e.g., from a photocell or microphone) for syn-

chronization of a single flash, or can be set to flash at a given rate for

multiple exposures. The entire system should be checked for proper

synchronization before the film is loaded into the camera.

Determining correct film exposure is simplified by the use of a

guide number (GN) that relates the lamp-to-subject distance (d) to the

camera-aperture setting (f):

The guide number, as determined from Figure 2-5, is used for single-

flash applications. When repetitive flashing of the stroboscope is required;

the guide number must be multipled by a correction factor (Guide Number

Multipler - K) taken from Figure 2-6.

It is necessary in computing aperture setting to modify the distance

measured between the stroboscope and the subject. The light from the

unit must be considered as coming from a point 1.5 feet behind the front

Figure 2-5. Guide number versus film speed for Type 1531

intensity settings. Dots for single-flash operatian: see Fig-

ure 2-6 for correction required for repetitive fleshing.