Gels and Diffusion

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Definition

  • Diffusion changes the spectral quality which is the appearance of light reflecting off an object or person, of a light source. The size of the source or piece of diffusion, changes the quality of light. a larger source in relation to the talent will be softer. Placing diffusion in front of a light source changes the intensity as well.

Diffusion filters are used for softening and spreading a light beam and reducing the contrast ratio between highlight areas. Paper diffusion is used on 4x4 frames or smaller. There are a variety of different types of filters.

Diffusions: Spread the projected beam of light over the subject, some loss of light will possibly be seen. The greater the diffusion, the greater and more even the resultant spread of light. Shadows are reduced. Used to smooth out beam scallops when lighting cycloramas or in tight spaces.

  • Color Gel and Correlated color temperature (CCT) gel change the color make up of a source through subtractive coloring. Measurement of Color is calculated in degrees of Kelvin.

Example: Tungsten is usually rated at 3200 degrees Kelvin, or 3200k.

Types of Diffusion

Heavy Diffusion

  • Muslin, Grid Cloth, 216, Heavy Frost

Medium Diffusion

  • Silk, Spun, 250, Light Grid

Light Diffusion

  • Opal, Hampshire Frost, 251, 252, 1/4 grid
  • 216 White Diffusion - A strong diffusion used for soft light effects. Manufactured on a tough Polyester base in a range of seven strengths.
  • 250 Half White Diffusion - A medium diffusion used for soft light effects. Manufactured on a tough Polyester base in a range of seven strengths.
  • 251 Quarter White Diffusion - A weak diffusion used for soft light effects. Manufactured on a tough Polyester base in a range of seven strengths.

Frosts: Frost is used for a variety of applications offering low to medium diffusion to a beam of light while maintaining the shape and beam centre.

  • 129 Heavy Frost - A strong diffusion that eliminates nearly all shadows. Flame retardant.
  • Opal Frost - A weak diffusion used for softening spotlight beam edges without altering shape. Manufactured on a 23 micron polyester base.
  • Hampshire Frost - A light frost effect.

Troubleshooting

How to Skin a 4x4 Frame: https://www.boltlightingrental.com/wiki/index.php?title=How_to_Skin_a_4x4_Frame

Related Equipment

Cloth diffusion is used on anything larger than 4x4: https://www.boltlightingrental.com/wiki/index.php?title=Soft_Goods

Insert articles about cloth diffusion, nets/flags, how to build frames, setting up stands.

For more information on checking soft goods: https://www.boltlightingrental.com/wiki/index.php?title=How_to_Check_Soft_Goods

References

See https://www.leefilters.com/lighting/diffusion-list.html for more information


Light Loss for Common Diffusions

  • White Diffusion "216": 1 1/2 stops
  • 1/2 White Diffusion "250": 3/4 stop
  • 1/4 White Diffusion "251": 1/3 stop
  • 1/8 White Diffusion "252": 1/4 stop
  • Opal "410": 1/2 stop
  • Light Opal Frost "420": 1/4 stop
  • Hampshire Frost "253": 1/4 stop
  • Heavy Frost "129": 2 stops
  • Half Soft Frost: 1 1/2 stops
  • Magic Cloth: 3 stops
  • Grid Cloth "430" or Silent Grid Cloth: 2 1/2 stops
  • Light Grid Cloth "432" or Silent Light Grid: 2 stops
  • 1/4 Grid Cloth "434" or Silent 1/4 Grid: 1 stop
  • Full Tough Spun "214": 2 1/2 stops
  • 1/2 Tough Spun "215": 1 1/2 stops
  • 1/4 Tough Spun "229": 3/4 stop
  • Artificial Silk: 1 2/3 stops
  • 1/4 Silk: 2/3 stop
  • China Silk: 1 stop
  • Unbleached Muslin: 2 stops
  • Bleached Muslin: 2 stops

Light Loss for CCT Gel

  • CTB (Color Temperature Blue) "201": 1 2/3 stops
  • 1/2 CTB "202": 1 stop
  • 1/4 CTB "203": 2/3 stop
  • 1/8 CTB "218": 1/3 stop
  • CTO (Color Temperature Orange) "204": 1 stop
  • 1/2 CTO "205": 2/3 stop

1/4 CTO "206": 1/3 stop 1/8 CTO "223": 1/3 stop

  • CTS (Color Temperature Straw) "441": 1 stop

1/2 CTS "442": 2/3 stop 1/4 CTS "443": 1/3 stop 1/8 CTS "444": 1/3 stop

  • Plusgreen: 1/2 stop

1/2 Plusgreen: 1/4 stop 1/4 Plusgreen: 1/8 stop 1/8 Plusgreen: 1/8 stop

Minusgreen: 1 stop 1/2 Minusgreen: 1/2 stop 1/4 Minusgreen: 1/4 stop 1/8 Minusgreen: 1/4 stop

MIRED SHIFTS FOR COLOR CORRECTION GEL:

MIRED's are used for calculating color temperature conversions.

  • Lee's online MIRED calculator.
  • Rosco's Filter Facts: Mired Formula

Increase Kelvin

  • CTB (Color Temperature Blue)-131 MIRED (Converts 3200k to 5500k or 2900k to 5200k)
  • 1/2 CTB -68 MIRED (Converts 3200k to 4100k or 2900k to 3800k)
  • 1/4 CTB -30 MIRED (Converts 3200k to 3500k or 2900k to 3200k)
  • 1/8 CTB -12 MIRED (Converts 3200k to 3300k or 2900k to 3000k)

Decrease Kelvin

  • CTO (Color Temperature Orange) +167 MIRED (Converts 6500k to 3200k or 5500k to 2900k)
  • 1/2 CTO +81 MIRED (Converts 5500k to 3800k)
  • 1/4 CTO +42 MIRED (Converts 5500k to 4500k)
  • 1/8 CTO +20 MIRED (Converts 5500k to 4900k)
  • CTS (Color Temperature Straw) +160 MIRED (Converts 5500k to 3200k)
  • 1/2 CTS +81 MIRED (Converts 5500k to 3800k)
  • 1/4 CTS +42 MIRED (Converts 5500k to 4500k)
  • 1/8 CTS +20 MIRED (Converts 5500k to 4900k)
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