American Cinematographer - December 2017 - 20

medium gray, then stop down the lens
three more stops than the meter
recommends in order for the card to
appear as black in the image. Likewise,
if the white card is three stops brighter
than 18-percent gray, open up the lens
three more stops than the reading you
get with the spot meter so the card will
be rendered correctly.
Black, white and gray are easy
enough to figure out, but skin tones can
be more challenging. Just how much
brighter or darker than medium gray is
the actor's skin? Seasoned cinematographers draw on loads of past experience
in order to properly compensate
between what their meter reports and
what they know the true reflective value
of their subject to be.
The opposite of a spot meter is an
incident meter. You'll recognize an incident meter by what appears to be half
of a ping-pong ball. Incident meters
measure the light falling on the subject
being photographed; you take the
meter reading by placing the incident
meter between the light source and the
subject.
Like a spot meter, the incident
meter assumes that you are
photographing an 18-percent neutralgray subject. But, because you're
measuring the light falling onto the
subject rather than the light that's
reflected off, the incident meter has a
built-in conversion factor. If a black wall,
a gray wall and a white wall are all lit
with the same intensity of light, the incident meter will measure exactly the
same value and report exactly the same
stop recommendation. Again, this is
because it measures the light before it
hits the wall, not after it reflects off of
the wall. So, in essence, the incident
meter's assumption of the subject being
18-percent gray is moot. This also holds
true for skin tones and, indeed, objects
of any color or reflectance - and it
makes the incident meter significantly
easier to use, as it doesn't require any of
the spot meter's mental gymnastics.
Some meters actually combine
the functionality of both spot and incident meters. And if you own an SLR
camera with a built-in light meter, you
20

December 2017

already have a spot meter - any
camera with through-the-lens (TTL)
metering is, in essence, a spot meter.
The camera looks at the light reflecting
off of the subject and provides an exposure recommendation based on the
assumption that the subject is 18percent gray.
In addition to traditional standalone meters - whether analog or digital - there is, of course, an app. In fact,
there are several. For example, Pocket
Light Meter is an iOS and Android application from Nuwaste Studios that turns
a smartphone into a spot meter; recent
updates have also added color-temperature readings. Additionally, the Luxi
"ping-pong ball" attachment can be
purchased to slip over your phone's
camera and turn Pocket Light Meter
into an incident-meter application. The
accuracy of the readings is impressive.
I also recently had the opportunity to work with the Lumu iPhone lightmeter accessory. It's a device that plugs
into the iPhone's Lightning port, and it
can measure light intensity as an incident meter or color as a color meter. It
can also act as a flash meter for still
photographers.
Sekonic, Konica Minolta, Spectra
and Gossen are among the companies
that manufacture light meters.
Although they may not be as necessary
for primary exposure judgments in digital production, they're still handy for
taking measurements and gauging
lighting ratios for scenes that you might
need to re-create later. They're great for
getting an idea of your exposure levels
before the camera or monitor is up and
ready. They're useful for evaluating
lighting decisions based on where you
want to place certain subject values
within the camera system's dynamic
range. And they're perfect for location
scouting, light studies, and for measuring and maintaining atmosphere - fog
or haze - over the duration of a day.
Yes, light meters still have a place
in today's digital productions. And luckily for all of us, the options we have for
which meter to use are as vast as ever.

American Cinematographer

Deep Focus
The Ubiquitous Ks
If you're a baseball pitcher, nothing
would be more extraordinary than having
27 Ks on a single game's scorecard. If
you're a cinematographer, however,
you're bombarded by Ks on a constant
basis, and rather than being welcome,
they can be downright bewildering.
The discussion of Ks has become
something of a hot-button topic. Certain
exhibition venues and platforms demand
a minimum number of Ks. Producers have
a handful of questions for every K in
consideration. And many cinematographers feel at best that they kind of understand Ks. In this environment, misunderstandings abound. So let's try to clear
things up.
First off, there are many things that
"K" can stand for. Let's take a look at
them, one by one.
K can be the symbol for Kelvin, the
unit of measurement used for the colortemperature scale that we deal with on a
daily basis. Daylight is, roughly, 5,600K,
and tungsten light is approximately
3,200K. These numbers are based on the
scale created by William Thomson, the
Right Honorable Lord Kelvin (1824-1907),
who postulated that if you take a pure
black body that absorbs all light and emits
none, and you slowly apply heat, it will
start to glow - first red, then orange,
yellow, blue and, finally, white. The
"Kelvin scale" starts at absolute zero
(-273°C = 0K), the point at which all
molecular activity stops. When color film
was invented, it was decided that tungsten and daylight would serve as the two
target temperatures for "white" light. A
note about daylight: 5,600K is the nominal average of sunlight and skylight at
noon on a cloudless day; depending on
the source, daylight is also sometimes
expressed as 5,500K or 6,500K.
Next, K can refer to kilowatts, part
of our nomenclature for a lamp's electrical
power. Kilo is derived from the Greek
word for "thousand." So, when we're
talking about a 1K Fresnel, or a 4K PAR, or
an 18K HMI, those numbers designate
thousands of watts - kilowatts. That
Fresnel is 1,000 watts, the PAR is 4,000,

Table of Contents for the Digital Edition of American Cinematographer - December 2017