The SubStream's "Film Lab" provides valuable information for filmmakers, specifically cinematographers and gaffers, on how to use neutral density gels.
Gels are used to change the quality or color of the light in a scene. Gels can come in many different sizes: they can extremely small to go in front of a camera lens, just big enough to fit in front of a lamp, or they could come in huge sheets to cover a huge window. The gels used more than any other are ND gels, which stands for neutral density gels. ND's change the intensity of the light that passes through them. They don't change the quality or color of the light, just the intensity. The most common ND gels are ND3, ND6 and ND9.
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