Diffusion Filter

What this is about

Diffusion is baked in, and that is exactly why it is a prep topic. A grade can lower contrast, but it cannot make a practical bulb bloom the way glass does, so the DP tests filter families and strengths during camera prep and locks a choice for the film. Consistency then becomes a continuity job: the same filter has to sit in front of the lens for every angle of a scene, and the script supervisor or the AC tracks it like a lens choice.

A term only helps when everyone on set means the same thing by it — so what follows is how it is used, not a dictionary definition.

What runs differently here

Where this differs from the general case:

• Strengths run in fractional steps such as 1/8, 1/4 and 1/2, and the difference between neighbours is visible on skin.
• The effect scales with the highlights in frame: a filter that looks subtle by day blooms strongly around night practicals.
• Filter and lens interact, so tests should be shot with the actual glass rather than judged from a sample reel.

With TillyGen

TillyGen's equipment list keeps the filter set with the lenses and matte box, so the agreed diffusion travels with the package to every location.

Change one constraint and the consequences travel through the whole plan: affected shots are flagged, the call sheet is regenerated, and nobody keeps working from yesterday's version.