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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'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 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 Speed light 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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