Q&A: Feathering a Soft Box
I understand how this works with directional light (e.g., a bare speedlight) - but doesn't the softbox's flat white panel send the light in all the directions more-or-less equally, thus rendering feathering more or less impossible? Can you feather a shoot-through umbrella -- and how?
(a) No, (b) sort of -- and (c) lemme explain…
First off, the light in question here is a speedlight in a LumiQuest Soft Box III, but feathering will work with any soft box.
Light coming of of a soft box panel does not have a defined beam like a small light source inside a reflector would, but it still has some shape. Think of in terms of how much of the soft box panel you can see from different positions around the light.
If you are directly in front of it, you will see the full face of the soft box, and the intensity of the light you receive will be a function of how far away you are. But as you move around toward the side of the soft box, you will see less apparent surface area because of your angle of view.
You can use this "edge" of the light to control how light falls across your subject, as in this close-up portrait (more here) that I did with the same light source.
In that example, instead of pointing the light right at his face it was rotated around away from him (towards me) and also pointed further up than you would expect. This placed his face in the area where the intensity of the light is falling off, which is what gives you that nice gradient towards the camera-left ear and down his torso.
(If you need to get even more of an edge to a small soft box, that's an easy mod, too.)
The light is less than a foot from his face, and hand-held. That way, it is easy to look at the image popping up on the back of the camera and adjust the angle as you shoot. Kind of the ultimate voice-activated light stand, 'cause it's you at both ends.
Umbrellas (speaking of shoot-through versions here) are a different animal, because they present themselves as almost hemispherical -- sending the light out in almost a 180-degree pattern.
You can't really feather a shoot-through umbrella per se, but you can control the spill by partially gobo'ing it.
The photo at left is a good example -- more details and a diagram here.