From the course: Advanced Photography: Flash
See like a light
- In the 5th century BCE, Empedocles, who believed that Aphrodite created the human eye, postulated that the fire that burns in the eye shines outward, enabling us to see the world. I assume that I don't have to tell you that he was wrong. But, Empedocles's idea is actually helpful when it comes to lighting because it's easier to think about what a light does if you think about what parts of your scene a given light sees. I have this handheld flash here, and I've got Natalie sitting over here. So let's say that I'm going to light her with this flash from back here. Now, when the flash fires, some light's going to travel out of this side of it in a straight line and it's going to hit right in here somewhere. If I come back here, light from the other side is also going to travel and hit right in here. Now of course as we've already seen, the light's going to spread beyond that. There's going to be falloff on either side, but the main intensity of the light is going to be right in here. So what that means is that when I'm standing out here, this light at this distance sees a fairly small part of her face. Now there's something else going on too, which is the light's bouncing around inside of here a little bit, there's a lens on the front. So some light beams are coming out at little angles. So they're not all coming perfectly straight in parallel rows and hitting her, but they're mostly illuminating that little space. Now, watch what happens if I move up to here and do the same thing. Now when I trace a line, from the right side, it hits over here. If I trace a line from the left side, it hits further to this side. Similarly, the light that's bouncing around is coming out at more angles. Some of it's going to be able to get on this side of her nose. In other words, as the light gets closer to her and attains a size that is larger relative to her, I get different coverage and I get softer light. The reason I get softer light is more of those other angles are able to hit her face. This is easier to understand with a big modifier like this. This is a big softbox. It bounces light around a whole bunch inside and then sends it out through this diffusion panel which scatters the light further which means that this light is seeing a lot more of her face. So some bits of it are coming in and hitting on this side of her nose, other bits are coming in and hitting this side. It means that more of her face is illuminated, but more importantly, it means that lots of shadow areas are getting filled in. There aren't going to be any hard, dark shadows, because light can come from so many directions. This light sees more of her face and it's able to fill in a lot of the shadows. In other words, this light, because it's so large relative to her, is much softer than this light was way back there which was very small relative to her. Obviously because of falloff, as I move my light closer or farther, my subject will get brighter or dimmer, so I have to alter the power level on my light to compensate. We're going to return repeatedly to the idea of what a light sees because it's a great way to figure out an answer to our fourth critical question, where does light go once it has left the lighting instrument?
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