Sekonic L-398 - Luminance range center point; Determining subject luminance range; To obtain superior color photographs

Shown
here isan
example
of using
Lumisphere
and
by
normal
measuring method
without
slide,
meter
needle indicates
640
foot-
candles. With
film
sensitivity of
ASA 100, exposure
becomes
f
45
and shutter speed
1
second.
H
mark
at this
time
indicates
20.
This 20
indicates
the
exact
center
point
of the
luminance range.
In the
same
condition,
install Lumigrid
and
when standard
reflectivity
of 18%
is measured,
this
means
that
the dial scale
will
ind icate 20.
When
determining
exposure
by
using the Lumisphere
or Lumidisc,
the
H
a
mark
will
always
indicate
the center
of
luminance range,
regardless
of whether or
not
the
High
slide
is inserted.
lf
the
measured
value is
set to the dial scale L
^
mark
and
the
H
a
mark
does
not
reach the
scale,
reflected light measurement
with the Lumigrid cannot be
performed
due to
insuff icient
incident
light
strength.
In other words, af
the
incident
light is less
than
160
footcandles,
ref lected
light measurement cannot
be
performed
with
the Lumigrid.
2. Determining
subject
luminance range
a.
Install Lumigrid
in
place
of Lumisphere and
remove
any
installed
slide.
Since the meter
needle
ind icates relative
luminance,
employ meter
scale
@
value
to compute
the
luminance ratio.
27
Hold
meter
about 1Scm
from
the subject,
point
Lumigrid
to
each
surface of
the
subject and read
the
footcandle
scale value.
To determine
the luminance
range,
it is
sufficient
to
divide
the
highest meter
indication
by
the
lowest.
For example,
if
the
highest value
is
80 and the lowest
5, the luminance range
becomes
80/5
=
1611
or 16 :
1.
Lumi
nance range
measurement
To obtain superior
color
photographs,
determine upper
and
lower limits.
Adequate
color
photographs
can be obtained with typical color
film
if
within
the subject
luminance
distribution, the
maximum
is fess
than 4 times
the center
point
and
minimum more
than
114
times
(
i.e. :
overall luminanc€ range
becomes
less
than
1
6
:
1
).
With
a
luminance
center
point
of 20,
if
the
measured maximum
luminance
is higher
than
80
(center
point
20
x
4
=
80), color
of
that surface
will
become
faded in
the
photograph.
Consequently,
a
slight
reduction
of
incident light to
this
portion
.becomes
requ ired.
Conversely, a
portion
with
a
measured minimum
luminance less
than
5
(center
point
20
+
4
=
5)
requires increased illumination
in
order
to
obtain
an acceptable
col<ir
photograph.
28
b.
c.
3.
a.
b.
c.
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