Last week, I did a few tests with my Nikon SB-800 flash and some dome light modifiers to see how they affected the light. The idea came about from a combination or sources, but it was essentially regarding whether or not a dome diffuser softens the light. Some people claim it does, but that flies in the face of everything I've learned. Quality of light (soft or hard) comes from the “apparent” size of the light source to the subject. Dome diffusers scatter the light so it will bounce off a larger reflective surface (like a wall or ceiling). It's that reflection from a larger source that becomes the apparent light source to the subject; not the flash itself.
So while last week's intent was to look at how modifier's scatter the light, we didn't really look at its effect upon a subject. That's the purpose of this post. Once again, I've pulled out my gear to put the ideas to the test.
I'm shooting with a Nikon D700 mounted on a tripod with my SB-800 to camera left on a stand, just half-arm's length away. Here are my settings for the shots:
- ISO – 200
- Aperture – f/16
- Shutter 1/200
- Focal Length – 70mm
- Flash Power – 1/4
Both camera and flash were mounted on stands to keep everything still and consistent, and I was able to find a model who didn't move a bit. Everything stayed consistent, except the first shot. I just wanted to verify that I wasn't getting ambient light on the subject.
Success! I can't see a damn thing, so we don't have to worry about ambient light contaminating the flash test results. Now let's see how our subject looks with a bare SB-800 flash.
It's about what you'd expect from an off-axis flash. You can see some shadow on the right side (or subject's left). It's not glamourous by any stretch of the imagination, but it defines the subject. Now let's see what happens when I add the dome diffuser.
The first thing you notice is a sharp drop in light on the subject. However, take a look at the same areas where shadow was defined, particularly where the subject's left ear would be (if he had one), on the subject in the previous example with bare flash. The amount of light is lower, but it's just as harsh. Both images lose detail in dark shadow by that ear. The diffuser did nothing to soften the light. It can't, because it's the same size in relation to the subject as the bare flash. Without any reflection or bounce off a larger surface, the dome diffuser does nothing to soften your light. However, let's take it a step further. What happens if we put a snoot around the flash & dome to ensure the light doesn't travel around and bounce off a wall or my (high) ceiling?
I used a Honl SpeedStrap and Snoot on this shot, wrapped around the SB-800 and dome diffuser. No bounce off the walls. The quality of light isn't any softer coming straight out of the dome. If you look at the defining shadow areas (what you can see here), they are just as harsh as the bare flash.
I decided to play a bit more by putting the Honl grid on the flash. There's no dome in this shot, just flash right through the grid.
I love grid spots for the way they channel the light where you want it to go. However, the shadows remain as hard as always. Now let's take a look with a larger light source.
This shot used an Alzo Digital softbox. It's essentially the same type of box as a Lastolite EzyBox. Once again, you see that the diffusion material reduced the amount of light falling on the subject. There are still defining shadows on the subject, but some of the detail in his beard near the subject's left ear starts to come out of the harsh shadow. With a larger light source, you begin to see detail that was previously obscured. However, it's still too dark.
In this image, I moved the softbox a bit closer to the subject. Notice how the detail in the beard by his left ear is no longer hidden in black. It's still in the shadow area, but you can make out information that a smaller, harsher light source obscures. You still have shadow and definition, which you want, but the fall-off into those shadows is less severe now. That comes from a larger apparent light source.
You want to get that light as big, and as close, as you can to your subject in order to improve your quality of light. There's absolutely nothing wrong with using a dome diffuser to bounce light from other surfaces, but just be sure you understand what's really happening. I've seen people outdoors with their flash tilted up slightly and a dome diffuser on top. It's a waste of battery power. In order to get enough light on their subject, the batteries have to push harder to pump out more light to make up for the loss of light the diffuser causes by reducing the light that leaves the flash, and by spreading it in every direction – rather than right at the subject.
In short, know your gear and how it behaves in different circumstances. Take some time to shoot a few tests and look at the results. You may find something you like better than what you're doing now, or perhaps a way to make your gear work more efficiently.