Nikon N6000 - Manual (Page 124)

Fill-flash
A method of flash photography which combines flash illumina­
tion and ambient light, but does not necessarily attempt to
balance the two types of illumination.
Flash synchronization
The timing of the flash so it fires coincident with the operation
of the camera’s shutter. There are two types of synchronization:
Normal Sync which fires the flash at the start of the exposure,
and Rear Sync which fires the flash at the end of the exposure.
f-number
Number which indicates brightness of film plane image. In-
creasing/decreasing f-number is opening/stopping down lens
aperture. The f-number series is equivalent to 1.4, 2, 2.8, 4, 5.6,
8,11,16, 22, 32, etc. Changing one step to the next larger
number (i.e., from f/11 to f/16) decreases image brightness by
1/2; moving to nearest lower number doubles the brightness.
Guide number
The number given to a flash bulb or electronic flash unit to
indicate its power. A guide number may be quoted in meters
or feet, and depends on the speed of the film being used.
Guide numbers quoted assuming a relatively efficient reflector
surrounds the flash source, e.g., an average-sized room.
ISO film speed
The international standard for representing film sensitivity
(speed with which it reacts to light). The higher the number, the
greater the sensitivity, and vice versa. A film speed of ISO 200
is twice as fast as ISO 100, and half the speed of ISO 400 film.