American Cinematographer - October 2017 - 14

SHOT CRAFT

A Fresnel lens incorporates concentric circles in order to reduce a
plano-convex lens' mass while retaining its qualities.

Fixtures 101: Fresnel, ERS, PAR
By Jay Holben

For the emerging cinematographer, one of the most intimidating challenges can be determining which lighting fixture to use at
any given moment. With experience and time to experiment, you'll
develop your personal preference - but that doesn't help the first
time you have to put together a lighting order! So, to give you some
guidance, let's break down three common lighting fixtures and
examine their attributes and common applications.
A fixture without a lens - commonly called "open face" -
spreads the light outward in all directions from the source, most
often creating a large, uncontrolled and unrefined field of light. A
lens is required to concentrate the light rays and make the fixture
more efficient, controlling and maximizing its output.
When a ray of light comes in contact with an object, it can
reflect off that object's surface, be absorbed by the object, or be
transmitted through it if the object is translucent or transparent; to
various degrees, it can also be reflected, absorbed and transmitted,
which is what happens when light strikes a flat piece of glass, like a
windowpane. Most of the light passes through, but not without
some alteration to its path. The light is slightly slowed down, and its
direction is changed while inside the glass. This is called refraction. A
lens, which is a piece of rounded glass, is designed to refract light in
a specific manner so that its exit path is different from its entrance.
One of the most basic types of lenses is the plano-convex lens,
which has one flat side (plano) and one convex side. Light passing
through the lens refracts considerably, and the direction of the exiting light rays depends on the distance between the lens and the
actual source. At the proper distance, the light rays hit the plano side
14

October 2017

The Fresnel
In the early 1800s, French engineer and physicist AugustinJean Fresnel was working to create a large lens for lighthouses. The
trouble was that, given the large lens-diameter required, the glass
became far too heavy and was impossible to work with. Fresnel
discovered, though, that by starting with the plano-convex shape
and cutting away at the lens in concentric circles, he could retain the
lens' qualities while greatly reducing its mass.
The resulting "Fresnel lens" was adopted into theatrical and
motion-picture lighting almost as early as artificial light itself. Relatively lightweight, this workhorse lens allows light to be efficiently
utilized in a soft, even field. Fixtures with Fresnel lenses most often
have both "spot" and "flood" functionality, whereby the lamp
inside the fixture is moved away from or closer to the fixed lens, forcing the light rays to converge or diverge, and making them into a
tight circle (spot) or a wide one (flood). Spotting-in a fixture intensifies its brightness, whereas flooding spreads the rays over a larger
area and therefore reduces the overall intensity at a given distance.
Mole-Richardson, one of the oldest manufacturers of lighting
fixtures for the motion-picture industry that is still in operation today,
has many Fresnel instruments to choose from, each with a different
aperture and lamp wattage - as well as a nickname that has
become standard in industry parlance. In its incandescent (tungsten)
line, Mole-Richardson offers:
Midget
Tweenie
Baby
Junior
Senior
Tener

200 Watts
650 Watts
1,000 Watts
2,000 Watts
5,000 Watts
10,000 Watts

415⁄32" Fresnel
415⁄32" Fresnel
6" Fresnel
97⁄8" Fresnel
14" Fresnel
243⁄4" Fresnel

Even though the 10K fixture has a 2'-diameter Fresnel and
the Midget has a 4.5" Fresnel, the lenses of both refract light in the
same way - just with widely different intensities and sizes of the
light beams, determined by lamp wattage and lens size, respectively.
Other manufacturers - such as Arri, De Sisti and Altman - offer
their own lines of tungsten Fresnel fixtures in similar wattages and
physical sizes. Fresnel lenses are also often seen on HMI fixtures, and
even as an accessory to a PAR fixture, which we'll discuss shortly.
The Fresnel offers an even field of light that is considered
"pleasing" on the face. It can be used clean (without diffusion) on

American Cinematographer

Photo on this page from the AC archives. Additional images courtesy of Jay Holben.

of the lens, refract, and exit the convex side in a parallel fashion. If
the source is moved farther from the lens, the light rays refract to
converge upon themselves, forming a tight pool of light; if the light
source is moved closer to the lens, then the rays diverge, forming a
wider pool. In all three cases, the introduction of a lens forces the
light rays into a more efficient and controlled path.

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