How does this piece of glass master your light?

The world of lighting hardware can be confusing to navigate. There are so many different options, so many different types of fixtures, quality of illumination, and methods of creating same. How do you know which is the right one to use in a given situation?

To help a bit in understanding the different types of fixtures and their applications, I’m going to discuss one in specific, identified by the type of lens it uses: the Fresnel (seen above, with an example of a common Mole-Richardson Fresnel fixture).

In a fixture without any lens, commonly called “open face,” the light emitted spreads out in all directions, more or less evenly, from the source. Most of the time this creates a large, uncontrolled and unrefined field of light. A lens is required to concentrate the light rays and make the fixture more efficient for controlling the light.

With a flat piece of glass, a light ray will strike one side of the glass, refract (bend or deflect) slightly passing through and then refract again on its way out. The combination of these two refractions results in the light ray continuing on in exactly the same path as when it started. A lens, in any form, 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. As the name describes, the plano-convex has one flat side (plano) and one convex side. Light passing through the lens refracts considerably, but the direction of the exiting light rays depends on the specific distance to the actual source.

LIGHT AND A LENS: On far left, light passes through a glass flat with minor refraction. But light passing through a plano-convex lens will either focus or diffuse, depending on the distance of the source from the lens. The Fresnel lens design, on far right, has the same attributes as the plano-convex, but eliminates weight.

When the source is set at the proper distance to the plano side of the lens, the light rays are refracted and exit from the convex side of the lens in a parallel fashion. If the source is moved farther away from the lens, the resulting light rays are refracted 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.

In the early 1800s, French physicist Augustin-Jean Fresnel was working to create a large lens for the massive fixtures used in lighthouses. The challenge with the plano-convex lens was that it was impossible to create a large-aperture (diameter) lens for oversized applications, as the amount of glass involved became far too heavy and difficult to work with. But by starting with the plano-convex shape and cutting away the mass of the lens in concentric circles, Fresnel determined he could retain the qualities of the lens while greatly reducing its mass.

The Fresnel lens was adopted into theatrical and film 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 a “flood” and “spot” function on them, which literally moves the lamp and socket inside the fixture further away or closer to the fixed lens. This forces the light rays to converge or diverge, making them into a tight, smaller circle (spot) or a large, wide one (flood). Of course, spotting in a fixture intensifies the brightness of that smaller spot where as flooding (diverging) spreads out the same light rays over a larger area and reduces the overall intensity of the light 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 (seen above), each with a different aperture and lamp wattage — in addition to fun and funky names that have become ubiquitous in the industry, whether or not you’re using a Mole fixture.

In the Mole-Richardson incandescent (tungsten) line, they offer the Midget (200W 415⁄32" Fresnel lens), Tweenie (650W 415⁄32" Fresnel), Baby (1K 6" Fresnel), Junior (2K 97⁄8" Fresnel), Senior (5K 14" Fresnel) and Tenner (10K 243⁄4" Fresnel). Even though the "Big-Eye" 10K fixture has a 2' diameter Fresnel lens, whereas the Midget has a 41⁄2" Fresnel, they both refract light the same through their Fresnel lenses. In both cases the lens performs the exact same function, just with widely different intensities (determined by lamp wattage) and sizes of the light beams (determined by size of the lens). Other manufacturers, such as ARRI, DeSisti and Altman, offer their own line of Fresnel fixtures. Fresnel lenses are also often seen on HMI fixtures, even as an accessory to a PAR (parabolic aluminized reflector) fixture.

The Fresnel offers an even field of light that is considered “pleasing” on the face. It can be used clean (without diffusion) on a person without creating a harsh or unappealing look. A Fresnel doesn’t have the same “throw” that a spotlight does, meaning the light doesn’t necessarily travel well over great distances, but is more often used closer to talent or subjects. The Fresnel can, of course, be used through diffusion or in a softbox — such as a Chimera — but they aren’t necessarily as efficient behind diffusion or in a softbox as an open-face fixture might be

Because Fresnel fixtures have their flood and spot function, they are very versatile fixtures, adapting to coverage and intensity needs without requiring additional hardware. Since the rays of lights are refracted in a focused pattern, they can be easily cut with flags. Fresnel lens fixtures require a single-point light source, such as an incandescent bulb or a gas-discharge lamp (HMI). They cannot be used with fluorescent or multi-LED lamps. And since they’re a single-lamp source, there’s no danger of multiple shadows from a lone light.

The Fresnel is a true workhorse in all aspects of production lighting — for film and digital. Small, affordable packages of Fresnel fixtures are put together by ARRI in their own cases to start your lighting kit. They are versatile enough to work in many applications, and having a few of them in different sizes and wattages will cover many possible scenarios you’ll encounter in your lighting.