Nikon N75 - Page 122

Glossary-continued
Flexible Program
Flexible Program function temporarily shifts an
automatically selected shutter speed l aperture
combination whi le maintai n ing correct exposure .
That is , the desired shutter speed or aperture can
be selected in Auto-Multi Program.
f-number
The f- number represe nt s th e aperture va l ue and is
calculated from lens ' focal length divided by the
effective aperture open in g. The standard numbers
for calibration are 1, 1.4 , 2, 2.8, 4, 5.6, 8, 11 , 16 ,
22 , 32 , etc.
The smallest f- number is called maximum aperture
and the largest f-number is called minimum
aperture. Lenses with large maximum apertures
( smaller f- numbers) are ' fast ' lenses that allow
photographers to use faster shutter speeds in dim
light. Lenses with smaller maximum apertures
(larger f- numbers) allow the use of lower shutter
speeds for available light but are also lighter and
smaller than faster lenses. With some zoom lenses ,
aperture varies depending on the foca l length
setting .
Focal length
The distance from the principal point to the focal
point. In 35mm-format cameras , lenses with a
focal length of approx . 50mm are called normal or
standard lenses. Lenses with a focal length l ess
than approx . 35mm are called wideangle lenses ,
and l enses with a focal length more than approx.
85mm are called telephoto lenses. L enses which
allow the user to continuously vary the focal length
without changing focus are called zoom lenses.
122
Focus Tracking
Enables the camera to ana l yse the speed of a
moving subject according to the focus data
detected , and to obtain correct focus by
anticipat ing the subject's position-at the exac t
moment of exposure .
Lock-OnTM 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 insta nt after the front curtain of a
focal plane shutter has completed its travel across
the film pl ane . This is the way the N751N7500
operates w it h the flash sync mode at Normal Sync .
(See " Rear-Curtain Sync" .)
Guide number
The guide number indicates th e power of a flash in
relation to ISO film speed . The guide number of the
built-in Speedlight of the N751N7500 is 12139 (ISO
100 , m/ ft .). Guide numbers are quoted in either
meters or feet. Guide numbers are used to
calculate the fl stop for correct exposure as follows:
guide number
fl stop = -------
flash-to-subject distance
Using a se l ected aperture , we can calculate the
required flash-to-subject distance with the formula :
guide number
flash-to - subject distance = -=----,-,-----
fl stop
Useful for determining the maximum flash-to -
subject distance for flash photography .