Pentax digital spotmeter - IRE (Institute of Radio Engineers) Scale

IRE
{INSTITUTE
OF
RADIO ENGINEERS)
The
Pentax
Digital
Spotmeter
is
provided
with
an
IRE
Scale
which is
very
usef ul
f
or
television
f ilm ing
and
movie mak
ing,
as
well
as
genera
I
photography.
12O
Pentax
Spotmeter II's
equipped
with IRE
Scales
inrBre used
to
provide
exposure
settings
for
the
making
of
the
off icialf ilm
of
the 1
964
Tokyo
O lympics. Since that time, this
scale
has
come to
be
used whenever comoarable
precision
in
exposure
setting is called
for.
SCALE
IRE
units
provide
a
means
for
the
percentage-
wise comparison of
energy.
The
maximum
energy
value
is taken to be
1OO%
and
energy
levels
taking
this
maximum
as a standard are
expressed as
percentages
of maximum level This
method is
used in
radio
communications to compare signal
voltages,
but
is
also applicable to
the comparison
of light energy obtained in
exposure
measurements
The
light level of
the
brightest highlight in the
subject is taken
as
1
OO% and
the energy of other
parts
of
the
subject
is expressed in I
R E units
as
a
f raction
of
that level.
lndex 10
(1OO%
lR E
)
indicates the
level of the
brightest
highlight
in the
picture,
the
upper
bright-
ness limit,
and
is called the
"white
level
"
f
ndex
1
(O%
| R
E
)
shows
the
max imu
m
dark
ness
of
shadow
detail reproducible
on the
f
ilm. This
is
ca I led the
"
B lack level.
"
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