Nikon F55 Instruction Manual - Page 55
Focus Tracking, Front-Curtain Sync, Guide number, ISO film speed, Slow Sync, Vignetting
UPC - 074101484663
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MISCELLANEOUS Glossary-continued Focus Tracking Enables the camera to analyse the speed of a moving subject according to the focus data detected, and to obtain correct focus by anticipating the subject's position-at the exact moment of exposure. Lock-On™ Autofocus keeps focus firmly on a main subject during Focus Tracking even if some other object momentarily blocks it in the viewfinder. Front-Curtain Sync The flash fires an instant after the front curtain of a focal plane shutter has completed its travel across the film plane. This is the way the F55/F55D operates with the flash sync mode at Normal Sync. Guide number The guide number indicates the power of a flash in relation to ISO film speed. The guide number of the built-in Speedlight of the F55/F55D is 12 (ISO 100, m). Guide numbers are quoted in either metres or feet. Guide numbers are used to calculate the f/stop for correct exposure as follows: guide number f/stop flash-to-subject distance Using a selected aperture, we can calculate the required flash-to-subject distance with the formula: guide number flash-to-subject distance = ------- f/stop Useful for determining the maximum flash-to-subject distance for flash photography. ISO film speed The international standard for representing film sensitivity. The higher the number, the greater the sensitivity, and vice versa. A film speed of ISO 200 is twice as sensitive as ISO 100, and half that of ISO 400 film. Slow Sync A flash technique for using the flash at a slow shutter speed. Flash shooting in dim light or at night at a fast shutter speed often results in a flash-illuminated subject against a dark background. Using a slower shutter speed with the flash brings out the background details in the picture. The F55/F55D's Slow Sync mode extends the automatically controlled shutter speed range down to 30 sec. (in Auto-Multi Program, Aperture-Priority Auto) or 1 sec. (in h Night Portrait mode). Vignetting Progressively diminished illumination on the film from the centre to the corners. There are two kinds of vignetting-natural vignetting caused by the lens, and vignetting that is caused by improper use of accessories such as a lens hood or filter. 108 109