Photometrics of diffusion placement/4ft vs 2ft on Kinoflos

[Jeremy M Lundborg]

Curious about the properties of diffusing a lamp nearer to the bulb versus skinning a frame and placing it on a stand to fill the diffusion in the frame.

 

I've heard both schools of thought contending that diffusing on the lamp itself is a great way to keep things tidy and still diffuse. Conversely, diffusing further allows the diffusion to be filled by the light and properly spread the light.

 

Is this difference negligible between attaching diffusion on the bulb of a kino versus the barn door of a kino.

 

Bonus question: The difference between 4ft and 2ft on kino ballasts...is there any increase in a green spike or otherwise when using 4ft? I've heard you shouldn't play them on 4ft unless necessary.

[Stuart Brereton]

When you place diffusion in front of a lamp, the diffusion becomes the source for the purposes of softness. The larger the diffusion the softer the light. Placing diff on the barndoors of a 1kw lamp creates a source say 1' x 1', the same lamp through a frame creates a source 4' x 4', which will be much softer, assuming the same distance to subject.

 

Attaching diff directly to a kino tube acts more to reduce the intensity of the tube than to soften it, as you are not increasing the surface area of the source. Diff on the doors softens them slightly. Putting them through frames works against the whole idea of kinos, that they are a convenient, shallow profile, soft source. Of course, people do it all the time, but it is sort of counter-intuitive.