Diffusion differences

[Andy Jarosz]

Can someone please be so kind as to explain the difference between atlantic frost and white diffusion?

I just put both side by side on a 2k, and all I can tell without a real test is the Atlantic lets more light through. Obviously, this is the most scientific test in the world.

Thanks.

 

[David Mullen ASC]

Put the diffusion on a frame -- the softness of a source is determined by its size relative to the subject's distance. When you shine a light through a frame of diffusion, the surface of the diffusion becomes the effective source, and the broader, larger that source is, the less sharp the shadows it will create will be. So the differences in diffusion, other than some textural issues, is mainly about transmission versus spread -- i.e. heavy material spreads the light more evenly but allows less intensity to get through.

If you put diffusion on the doors of a light, then the size of the source is just whatever the distance is between the barndoors, often something like a 1'x1' diffused source, which is not particularly large. Create a 4'x4' frame and put your 2K behind that. Once you fill the frame evenly from edge to edge with no hot spot, you've reached maximum softness since it's determined by the size of the source -- at that point, doubling the diffusion or going heavier doesn't really make it any softer, you are just wasting output.

But there are definitely many degrees of softness because often a light behind the frame doesn't evenly fill the frame and it's hotter in the center.

If you use certain fabrics, you may even get the effect of a sharp source coming through the loose weave of the fabric surrounded by soft light that is coming through the rest of the fabric, sort of a hard/soft effect because there is some specular (sharp) light leaking through. Silks can have this effect. Just shine the light through the material and look at it from the other side -- if you see a light pattern in the material, like a star pattern let's say, then that sharper light is creating certain odd shadow effects.

 

[Evan Prosofsky]

Put the diffusion on a frame -- the softness of a source is determined by its size relative to the subject's distance. When you shine a light through a frame of diffusion, the surface of the diffusion becomes the effective source, and the broader, larger that source is, the less sharp the shadows it will create will be. So the differences in diffusion, other than some textural issues, is mainly about transmission versus spread -- i.e. heavy material spreads the light more evenly but allows less intensity to get through.

If you put diffusion on the doors of a light, then the size of the source is just whatever the distance is between the barndoors, often something like a 1'x1' diffused source, which is not particularly large. Create a 4'x4' frame and put your 2K behind that. Once you fill the frame evenly from edge to edge with no hot spot, you've reached maximum softness since it's determined by the size of the source -- at that point, doubling the diffusion or going heavier doesn't really make it any softer, you are just wasting output.

But there are definitely many degrees of softness because often a light behind the frame doesn't evenly fill the frame and it's hotter in the center.

If you use certain fabrics, you may even get the effect of a sharp source coming through the loose weave of the fabric surrounded by soft light that is coming through the rest of the fabric, sort of a hard/soft effect because there is some specular (sharp) light leaking through. Silks can have this effect. Just shine the light through the material and look at it from the other side -- if you see a light pattern in the material, like a star pattern let's say, then that sharper light is creating certain odd shadow effects.

Hi David,

You said "But there are definitely many degrees of softness because often a light behind the frame doesn't evenly fill the frame and it's hotter in the center."

Is this why I read about people such as Roger Deakins using 'double diffusion'? ie. A huge 18k shone through two layers of diffusion material. Are you an advocate of this technique? Or do you find this to be counterproductive.

Thanks!