Nikon 3699, 3700, 55 Focus Tracking, Front-Curtain Sync, Guide number, ISO film speed

Glossary-continued

Focus Tracking

Enables the camera to analyze the speed of a moving subject according to the focus data detected, and to obtain correct focus by anticipating the subject'sposition-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 N55 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 N55 is 12 (ISO 100, m). Guide numbers are quoted in either meters 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.

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