Fresnel Light

Sursa Fresnel .

The Fresnel is one of the most flexible fixtures to work with, being designed to create a relatively even field of light with adjustable intensity and field size. The light form a Fresnel makes clean, hard shadows. Its clean beam makes it a good choice for lighting actors' face, either directly or through diffusion. For these reasons, it is the most commonly used fixture in film and television.
The light is named for its Fresnel lens, witch bends the diverging rays of light emitted by the bulb into a controlled beam of light. The Fresnel lens has the same light-bending characteristics as a standard plano-convex lens, but the Fresnel's design compresses the convex curve into jagged steps, making it lighter and thinner so that it retains less heat.
Equally important, the fixture uses a spherical reflector. Because the bulb is at the focal point of the spherical reflector, light rays coming from the back of the bulb are reflected straight back through the bulb ( not directly out in front of the fixture, as in a parabolic reflector). All light therefore emanates from a single point with the fixture (the bulb), which is what allows the Fresnel lens to control the beam so cleanly.
Inside the housing, the globe and spherical reflector are mounted together and can be moved toward or away from the lens by an exterior adjustment knob. Moving the globe and reflector toward the lens floods the beam, increasing the spread and decreasing its intensity . Moving the globe and reflector away from the lens spots the beam, making it narrower and more intense. The adjustable focus makes it quick and easy to obtain the desired intensity or beam width.
Fresnel Accessories : 

  • Scrims : are a stainless steel wire screen used to reduce the intensity of the light. A single scrims has a loose wire weave, is identified by its green ring frame, and cuts the intensity of the light by approximately a half stop. A double scrim has a tighter wave, is identified by its read ring frame, and cuts the light by approximately one full stop. A standard set of scrims includes a single, two doubles, a half-single, a half-double, and gel frame. Quarter scrims and graduated scrims are also available for some fixtures.
  • Gel Frame : used to hold light gels or diffusions in front of the light.
  • Barn Doors : provide the most basic control over the placement of the edges of the beam of a Fresnel or open-face fixture. Band doors typically have two large leaves and two smaller triangular ones.
  • Snoot : Snoots come in various sizes, from wide (called top hat) to very narrow (stovepipe). Some snoots are fitted with four rings with different aperture sizes so that you can adjust the beam width.
  • Focal Spot : a focal spot essentially change a Fresnel into a spotlight. The focal spot lens assembly creates a narrow, bright, event circle. Like an ellipsoidal reflector spotlight, a focal spot has framing shutters. It accepts design patterns called gobos and mattes, which can be projected and focused onto the scene. It has interchangeable lens tubes-wide beam and narrow beam. It also comes with a gel ring to add color gels.
  • Shutters : are like heavy-duty venetian blinds; they have rows of parallel slats that open and close. The shutter is mounted on the front of the light. The shutter can be controlled to smoothly reduce the amount of light getting to the subject. Shutters are frequently used to create a lighting effect; a sudden flash can be produced by opening and quickly closing the shutter.
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