Steve Wylie
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 p.1 #4 · Question regarding an umbrella softbox | |
Basically, the difference between a soft box and an umbrella is the degree of control over light spill that a soft box gives you. An umbrella spills light all over the place, due to it's shape, whether it's a shoot-through umbrella or a reflective umbrella. A rectangular (or an octagonal) soft box, particularly those with sides that extend beyond the face of the box, limits that spread. Another contributing factor to the quality of light in either a soft box or an umbrella is the color of the fabric in the interior of the modifier. A silver material will provide a more specular light, while a white interior will provide less specularity. Then, in front of that comes the diffusion fabric, which provides an extra degree of softness to the light. So there are several different factors that contribute to the quality of light from your modifier: spill, or the ability to control it; specularity, or the lack thereof; and diffusion. A soft box can provide all of these attributes, while a shoot-through umbrella can only provide diffusion. That said, each of these factors are affected by the size of the modifier and the proximity of the modifier to the subject. The closer the modifier (whether a soft box or an umbrella) is to the subject, the softer the light will be. Also, the larger the modifier is, the softer the light. Working together, this means that the "apparent size" of the light determines its softness. Thus, a small modifier placed very close to the subject will be softer than a large modifier placed far away.
The point of this, like just about everything in photography, is that the look you want depends on a lot of factors, including your composition (what's in the frame), what you want to light (versus what you don't want to light), and the quality of the light you want to achieve. Knowing what different modifiers are designed to light, and then where to place them, will determine the success of your lighting strategy.
Now, to answer your specific questions, by "broad fill" I mean providing a base level of light across a wide area. For example, I shoot dancers in a studio environment. Placing single strobe in a Varistar shoot-through umbrella up high, about 20 feet from a studio backdrop, I can light the entire backdrop that is also 20 feet wide within a relatively narrow variance (about a half-stop) from side to side. That is due to the shape of the umbrella, which spreads the light all over the place. I will then use an octagonal soft box, placed on either the left or right side, at an angle of about 30-45 degrees, to provide a highlight side on my subjects. That soft box is designed to control the spread of light, when aimed properly, so it does not inordinately affect the amount of light on my backdrop.
Your second question, relating to fast-paced indoor events where mobility is required, is a different matter. Your direct question relates to soft light, and my answer is the same as before; any light that is diffused will give softer light than one that is not (i.e. shoot-through vs. reflective). But again, it's a matter of control over your light. If I were shooting an event such as this, I don't think I would use a large shoot-through umbrella, unless you want broad coverage. Usually, in an event such as a wedding reception, or table shots of guests, you'll want a smaller light source. Dragging a light stand with an umbrella can be done, but it isn't really very practical. In those situations, I would more likely have a flash on camera with as large a speed light-mounted modifier as possible (e.g. a Rogue Flash Bender). However, if you're setting up a shooting environment where guests come to you to have photos made, a setup with a shoot-through umbrella can be ideal. It's a forgiving light modifier precisely because it casts light all over the place. Your main consideration, in this situation, is what kind of shadow does your light cast? Where is it; is it harsh or is it diffuse? Those are issues that can be addressed by careful placement of your light.
I hope this helps to clarify some of the factors in choosing a light modifier. I'd also suggest that you check out strobist.com, specifically his Lighting 101 series of lessons. It's free and very worthwhile.
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. Umbrellas in general don't "spill light all over the place", and it isn't necessarily correlated with shape (and asbolutely not with depth, contrary to what many would have you believe).
