Diffusion Confusion

[GregM]

I bought a photography book that really emphasized using a diffusion panel over a softbox for portrait work. One of the advantages was that you can not only vary the distance of the panel to the subject, but also the light source to the panel. (I know that a diffusion material becomes the light source but I think you know what I mean)

So I plug in my Lowel 250 watt Pro light and place a tripod about five feet in front of it. I get very sharp shadows as you would expect. If I place a frost diffusion gel in front of the light, but only about two inches away, the light is softened somewhat and the shadows are a little less defined. Well if I move this gel say twelve inches from the Pro Light, the shadows from the tripod are almost gone.

Having never used a softbox, is the diffusion material far enough from the light to mimic this effect? Nobody uses diffusion panels in video production that I can see but there seems to be an advantage to be able to adjust the distance from the light to the diffusion material as well as from the diffusion material to the subject.

Any thoughts on this?

I asked at another board and all the replies harped on the fact that the distance between my Pro Light and frost gel is irrelevant since the gel is now the source. To them I say try what I am suggesting and you'll see what I mean.

Greg

 

[Barry_Green]

Re: Diffusion Confusion

It makes a difference in that the pro-light is a very focused instrument, so if you put the gel two inches away, only a small portion of the gel will glow (a small hot spot), whereas 12 inches away, there's enough spread for the whole gel to glow. With a small glowing hotspot, it's basically still a small hard source, but if the whole gel glows then it's a larger softer source.

This is really not relevant with a properly-designed softbox. Softboxes have a large distance between the front and the lamp, but more importantly the sides are lined with reflective material (usually silver, sometimes white). What this means is that the light gets blasted forward, but any light that bounces off the front panel won't be lost, it'll bounce off the silver and then head out the front again. This gives the light a much more general "scatter", so with a properly-designed softbox the entire surface of the front panel will glow evenly.

 

[Jim Brennan]

Re: Diffusion Confusion

Some soft boxes also have a removable internal baffle, which is just another diffuser located between the bulb and the front of the box. It further softens and reduces the amount of light. It's no different than setting up 2 diffusion panels, except that the distance is fixed.

 

[xort]

Re: Diffusion Confusion

depends on the size and config of the softbox. most of the softboxes I see in use could use more distance between the light and the diffusion. but that makes them very big and impractical in many situations. I used to use a 4' X 4' or 6' X 6' frame with diff but it requires more gear and more manpower to set up. often you will need to box the frame in with flags to control the spill, more time and effort. so the softbox is a convienience and with that is some compromise. your observations are correct, now you need to deal with the realities of what your needs are.
The pro light is a very spotty light and so it won't easily fill a sheet at close range. time to shop other fixtures and see what their flood setting does, how wide a beam they throw at the flood setting. many manufacturers will provide info that states width of coverage at a given distance. use that to extrapolate who makes the widest fixture in the wattage you prefer.