Controlling Light

I've talked about how to balance ambient light with strobes quite a bit before. How ambient light is controlled by shutter speed and aperture where are strobes are only controlled by aperture. But I've never actually show you how that actually works. Today, I thought it would be great to do a little demo of how camera controls affect exposure.

First off, we'll play with shutter speed. The camera is set to 1/250 at f2.2 and ISO100. The lighting set up isn't important here, other than I am using two strobes here to light the chair. Almost all ambient light is being cut out by the high shutter speed, even though there's a very open aperture. This is the sync speed of the strobe with the camera. This means it takes 1/250 of a second for the strobe to fully discharge, so the camera can't be open less that 1/250 of a second or the full power of the strobe would be cut short. Technically, there are different sync speed for different power levels, but for this lets just call it 1/250 cause that's what it is for the 560 at full power.

Here's at 1/250. Almost goes to black in the background where the strobes don't reach.

 1/125. One stop brighter. There's some detail coming in now.

1/60. Another stop brighter.

 1/30. One more stop up. This could be a "good" exposer for a portrait, for example. The background would be there but not intrusive. The subject is still lit mostly by the strobes, but the shadows aren't quite as dark as if we where at 1/250. This is all very subjective, and varies on the situation. I'd use this exposer at say, a wedding or senior portrait in the woods. I don't want the background to over power the sitter, just add to the feel of the photo.

1/15. Now it looks as it would to the eye. It's properly exposed for the strobe and the ambient light. Makes for a rather boring photo, doesn't it? No drama to it at all.

1/8. Starting to have some blown out highlights here.

1/4. Now where two full stops over exposed. Not useable without heavy processing in post.

1/2. Really over exposed. Highlights have no detail and the mid tones are starting to go.

1 second. Completely over exposed. Not useable at all. Maybe, maybe with heavy processing but there's just no detail in the highlights. If you could make it work, it'd still look terrible compared to a properly exposed photo.










This was all shot at exactly the same aperture and ISO. There's no change in any camera setting except for the shutter speed. I slowed the shutter in one stop increments. As you can see, there is massive control to be had with just one camera setting. You can independently expose the background from your artificially lit subject. Most of the time you use this to underexpose the background, and make your subject pop more.

On to adjusting aperture. This is a quick demo to show how you can control your strobe by the aperture. I turned the lights off so there would be no interference from ambient light. Tomorrow I'll do something to show how you can adjust all your setting simultaneously to control the light.

 Here is an over exposed photo. The highlights are too much and the mid tones are too bright. This is at f1.4

Stopping down to f2, the photo now becomes properly exposed. The tonal range is correct, and theres detail everywhere we want.

Going to 2.8, we're starting to underexpose things. The shadows are crushed, and there's very little detail in the midtones.

f3.5, two stopes underexposed. This would be a very noisy image to bring back. It's easier to bring back overexposure than underexposure.

 f4, unusable. Even the mid tones are gone.

f5.6, barely even any highlights left.















That was a quick little demo to show how you can control your strobes without actually adjusting power levels. If you're strobe is too bright, stop down. You'll have to also lower your shutter speed to keep the same exposure of the ambient light, but we'll talk more about that tomorrow.

I hope you can begin to see the significance of this. With this, you can take complete control of your photo. Theoretically, if you had a powerful enough strobe to overpower the sun (which there are), and infinitely short sync speed (think leaf shutter), you could make any lighting condition you wanted just by adjusting your camera settings. This is why I love shooting with strobes, there's just no limit to what you can do with them. You literally can make you're own lighting conditions that could never, ever exist in the natural world. If you're really good, you can trick people into thinking that the lighting is real, and that you had no hand in it. Thats the sign of a true master. cough* cough* Gregory Heisler.

Anywho, see you tomorrow.