Last Updated 5 days ago
Filmmaking Dictionary: Letter F / Fresnel
Definition
A Fresnel is a lens with concentric stepped sections that reduce the thickness and weight needed for a conventional lens of comparable optical purpose. On a film set, “a Fresnel” usually means a lighting fixture using this type of lens. The name is commonly pronounced freh-NELL.
Film-lighting Fresnels provide a focusable beam, commonly adjustable between spot and flood. They can use tungsten, HMI or LED sources; the lens type does not identify the light-producing technology.
Spot and Flood
Spot is the narrower end of the fixture’s focusing range. Flood is the wider end. Changing focus changes the illuminated area and intensity distribution, even if the lamp power or dimmer setting stays the same.
In many traditional tungsten Fresnels, the lamp-and-reflector assembly moves relative to the lens. LED designs and attachments can use different arrangements. Follow the fixture’s controls and measured beam rather than assuming every Fresnel focuses by the same mechanism.
Beam angles vary between models. Two fixtures at “full spot” need not produce the same angle or centre intensity.
Quarter Spot and Intermediate Settings
Quarter spot is an informal way of describing an intermediate spot–flood adjustment. It is not a standard beam angle, power level or exposure value. Crews can differ over where they measure from, so confirm whether the request means moving partway from flood toward spot or adjusting from another reference.
For a repeatable setup, record the fixture, control position, distance and beam coverage. If the light has a calibrated beam-angle control, record that value as well.
The phrase has no shared measurement scale with quarter CTB, quarter CTO or quarter grid cloth.
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Beam Edge Is Different From Shadow Softness
A Fresnel’s beam can have a relatively smooth edge while the light still produces defined shadows. Beam-edge quality and shadow softness are different characteristics. A bare Fresnel at normal working distances is generally treated as a hard, directional source.
Barn doors help contain spill, but they do not turn a Fresnel into a projection fixture with sharply focused shutters. A flag’s distance from the source and subject affects its shadow edge.
To create a larger apparent source, the crew may bounce the Fresnel or send it through diffusion. Check how evenly the beam fills that surface.
Using a Fresnel on Set
- Set the fixture position and beam spread before making fine exposure adjustments.
- Check centre level and edge coverage; a focus change can alter both.
- Use appropriate barn doors, flags or other accessories to control spill.
- Record focus position and distance when a later setup must match.
- Observe the fixture’s heat, mounting and electrical requirements.
A tungsten Fresnel usually becomes warmer when dimmed. An LED Fresnel may hold its colour more consistently, but capabilities depend on the design and operating mode. LED housings and accessories can still become hot.
Practical Example
A Fresnel floods a large diffusion frame for an interview. Spotting it down may increase the level in the centre while leaving less of the cloth illuminated. The face can then change in both exposure and shadow quality. Check the result before treating the focus adjustment as a substitute for dimming.
A quartz-halogen lamp describes one possible source inside the fixture; Fresnel describes the optics. The lighting department guide puts those choices in production context.
A traditional redhead is an open-face fixture. It can also light a bounce or diffusion frame, but it does not use a Fresnel lens and should not be assumed to provide the same beam control.
Related Terms
Browse terms beginning with F or return to the filmmaking dictionary.