Nikon SB-5000 Reference Manual page 9

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FX format/DX format
Nikon digital SLR camera image area types (FX format: 36 × 24, DX format:
24 × 16)
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Guide number (GN)
The amount of light generated by a flash unit; as the number increases,
the light extends further. There is a relation represented by an equation,
GN = flash-to-subject distance (m or ft) × aperture f-number (ISO 100).
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Step
A unit of the shutter speed or aperture change; a change of 1 step halves/
doubles the amount of light entering the camera
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EV (Exposure Value)
Each increment of 1 in exposure value corresponds to a 1-step change in
exposure, which is made by halving/doubling shutter speed or aperture.
An aperture of f/1.4 and a shutter speed of 1 second correspond to EV 1
which provides correct exposure or proper brightness of the subject. As
the exposure value increases, the exposure of the film or imaging device
increases.
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Front-curtain sync/rear-curtain sync
In front-curtain sync, the flash fires immediately after the front curtain
is fully open; the subject frozen by the flash appears behind the blurred
movement. In rear-curtain sync, the flash fires moments before the rear
curtain starts to close; the blur of a moving subject appears behind the
subject and not in front, creating natural pictures.
A
A-8