Different types of diffusion

[Capi]

In terms of effect created, what is the difference between the different types of diffusion, namely frost, diffusion, and silk? What does each do to the beam? I'm never sure which to use in a given situation.

[joeboo46]

Well i'm sure someone will prove me wrong but i'm gonna take a shot at this I would consider all three "diffusion" however they do have different purposes they all diffuse he beam of light in one way or another. "Frost" is going to soften the edge of the beam of light it is typically not directional and depending on the density of the particular frost it will give you more or less of a "smooshed" edge much like running the lens tube forward or backward on an ellipsoidal unit. I tend to find using frost will give you a more consistent result when using to soften the edge of light. For example in side light I will use Rosco 119 to soften the edge instead of running the barrel, I've found it gives me a smoother transition between lanes and positions, I do the same for front washes if I do indeed not want to have hard edges on the beam. I've also used frost in some situations where three lights are not quite wide enough to cover an area and I don't have any other fixtures to fill in the holes sometimes it gives you just enough glow to make it work (I try not to do this but sometimes you have to cheat).

Silk is different but kind of does the same thing. Typically silk is directional, it will have what appear to be lines running through it. If you you were to put silk in an ellipsoidal pointing straight down at the stage with the lines running up and down stage it would diffuse the beam left to right and if you run the lines in the silk left to right it would diffuse the light upstage to downstage. If that makes sense, the beam of light would appear to oval shaped. I use silk in cyc lights all the time to help with the scallop pattern you get when strip light are placed close to the object you are lighting, I run the silk upstage to downstage thus diffusing the beam left to right helping to eliminate the ugliness that is scalloping.

Just remember when using frost it does change the fixtures transmission of light. i.e. The heavier the diffusion the less light you get out the front of the fixture.

I know this is fairly detailed in respect to my feelings on diffusion but I hope it helps.

[derekleffew]

Although written for film/video applications, much of Rosco US : Technotes : Filters : Diffusion Material also applies to stage lighting.