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FOCAL LENGTH
A prime lens has a fixed focal length and,
of course, a zoom lens has variable focal
length. Though familiar, the term “focal
length” is often misapplied. The focal
length of any lens is a fundamental optical
property, and is not changed by fitting the
lens to a different camera. Unfortunately,
as if to promote confusion, the lenses on
most digital compact cameras are
described not by their actual focal length
but by their “35mm equivalent”—i.e. the
focal length that would give the same
angle of view on a 35mm or full-frame
camera. However, an 18–55mm zoom is
always an 18–55 zoom, regardless of
whether it’s fitted on a DX-format
camera like the D5300 or a full-frame
(FX) camera like the D800. However,
because the D5300 has a smaller sensor
than the D800, the image that’s captured
shows a smaller field of view.
FX/DX IMAGE AREA
The original was shot with a 24mm lens on a
Nikon D700. The red rectangle shows the area
that would be captured using the same lens,
from the same position, on a DX camera like
the D5300.
187
THE EXPANDED GUIDE
LENSES
»
INTRODUCTION / FOCAL LENGTH
Nikon D5300 Ch7 184-207 P2 RY.indd 187Nikon D5300 Ch7 184-207 P2 RY.indd 187 19/02/2014 17:0819/02/2014 17:08
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