I have used large softboxes for my portraiture quite a while with good success. However, I come across the topic of diffusion vs size of the light source quite often.
While I know, that the relative size of the light source has profound impact on the softness of the light, diffusion is randomly thrown into this as well.
Things I also heard, is that diffusion simply controls specular highlights.
What I believe:
- a larger diffused light will produce a softer light than a smaller light.
- a small diffused light will produce almost the same light as undiffused when it comes to softness, the diffusion will only spread the light a bit more
- a very big light (in relation) but with very uniform rays, will still produce harsh light. So size can produce softness, but it is only the potential for it (a big anti-aircraft light as an exaggerated example)
I see a lot of fashion shooting to use a huge reflector, but without any diffusion. However, as the shape is not completely used as a perfect focus, the light will get some diffusion just by the reflection patterns, I guess. So that would provide some middle ground between harsh and soft.
So it seems that you have to have at least some diffusion going on, otherwise you cannot get the relative size to become relevant.
Can anyone elaborate in-depth how diffusion and relative size affect each other?