Some Observations about Lighting Modifiers

This week we are going to discuss a few things about lighting modifiers. With very few exceptions, lighting modifiers do just 2 basic things. They change the size and the shape of a light source. That’s really all they do. The differences between modifiers is how they achieve those two properties.

This week we are going to compare two modifiers of very similar size. One is a 35 inch Octobox with a grid and the other is 36 white umbrella.

35 inch Octobox vs. 36 inch Umbrella

The mechanical difference between these two modifiers is that the umbrella bounces the light from the flash head to the subject to obtain diffusion, where as the octobox mounts directly on the light and uses a diffusion panel to dissipate the light. The grid on the panel helps prevent spill (keeps more light in the general direction of the subject). Below is a photo of them mounted on a light.

Umbrella and Octobox

From what we know about basic light theory, the effective size of a light source determines the harshness or softness of the light. A larger light source produces a softer shadows and a small light source produces harsher shadows. Following that, these two modifiers should produce the shadow characteristics. Let’s take a look as see how that pans out.

This first photo was shot with the umbrella.

Umbrella

One obvious thing we notice about about this photo is the shadow. Most of it is uniform with feathering occurring  at the outside edges.

Octobox

Now look at the photo above that was shot using the octobox. The shadow looks quite different. It is much denser at the center with a larger area that is feathered. Why would these two lighting modifiers of equal size produce such different shadow characteristics?

The explanation can be seen when we step back and look at the overall set. The photo below is a photo of the set from across the room showing the light pattern produced by the umbrella.

Umbrella

Because the umbrella creates lots of spill, light is blasted all over the studio. We can see that light actually escapes through the back of the umbrella.

Octobox

The octobox has a much more defined light throw. The grid helps confine the light even more and makes it even more directional. (Notice that no light escapes from the back of the modifier).

Ok, so how does this explain the difference in the quality of the shadows? One word: bounce. Because the umbrella sprayed light all over the studio much of bounced back to the subject and softened the shadow. If this was shot in a large open field or in a large studio the effects of bounce would not be seen and the shadow characteristics would be nearly the same.

A side lesson to be learned from this experiment is that, if you are used to the performance of a certain modifier in your studio, when shooting on location you may experience different results. Remember that your environment can affect the quality of your light.

An FYI: if you look at the photos of studio, you’ll notice that ceiling panels are painted flat black. This was done to help reduce bounce and to keep control of the quality of shadows.

That’s it for this week. Thanks for reading.

-Ken