Wednesday, July 15, 2009

And how would you like that done?

Medium rare.

At least that's how I typically like my steaks done. But we're not talking about steak. We're talking about ambient light.

The problem with ambient light is that unlike (I typed unlight the first time LOL) flash, you can't really do much to control ambient light.

Or can you?

Sure, you can't really tell the sun "Hey, we're trying to do a photoshoot here, would you mind shining from a 45 degree angle from camera upper right? Oh and while you're at it can you give me a 1/250th exposure at f/2.8?" On the polar opposite of the spectrum you can't really make the cathedral candles any brighter or ask the priest to burn several hundred more because it's "too dark".

The question that I'm going to answer is "or can you?"

What you do have control over is how that light manifests itself through the lens and onto the digital image on the back of your camera. With regards to ambient light and nothing else, you can choose how bright and/or dark you want the foreground (subject) or background, but most likely you can't have both. With one light source, your background will likely have a different exposure than the foreground (subject) and therefore you must choose one or the other and not both.

We can do a simple mental exercise for a demonstration. If I stand with my back against the sun and ask you to take a picture of me one of two things can happen. The camera (or user) might expose for my face and white-out the background (sky/sun). Or the camera (or user) might expose for the background, where the sky will appear blue but my face will be completely black. Why does this happen? Because the bright summer sky requires a different exposure than my face which happens to be in the shade (remember my back is against the sun). The difference between the two will likely be several f-stops hence making one too dark/bright in any given frame.

As a caveat, if our background is not the sky but instead some nearby objects like trees, grass, and rocks, then we can hopefully expose for both at the same time without too many f-stops difference between foreground and background

With multiple light sources (read: strobes) you can now answer the question on the title of this post, "And how would you like that done?" Because with your own controllable light source, you are now able to mix and match the exposure of your foreground/subject with that of the background. Here are some examples:

In studio, I do not require any ambient light. Typically ambient light in my studio takes the form of window light through a closed shutter that might have a green tint to it because of the grass reflecting the light. Regardless, I have 11 strobes in my studio and I do not require additional light thank you very much. So the answer to the title question is, "I don't want any ambient light, thanks" Hence, I drown out all ambient light with a small aperture (f/9 or smaller) and the fastest shutter sync speed my camera can handle (1/250s).

When I'm outdoors however and shooting into the sun, I'm typically trying to preserve the colors of the background without taking any attention away from my subject. In this case, I usually underexpose the background by several stops so that the sky looks blue (otherwise the sky will look white like we talked about above). So the answer to the title question becomes, "I want a darker background". I accomplish this by putting a strobe (usually) at full power close to the subject so again I can use a small aperture with the fastest sync speed my camera can handle.

The last example I will provide is when we're shooting in the dark in some dungeon, cave, cathedral or wherever you might be where it's poorly lit. In this instance, you're likely trying to preserve all detail in the background and therefore must really open up that aperture and slow down the shutter speed in order to get as much light into the camera as possible. Unfortunately the drawback of a slow shutter means that we're not susceptible to motion blur so we're now either forced to use the tripod or increase the sensitivity of the camera (ISO) to the point where we can hand-hold the shot. Fortunately in darker environments the subject is just as dark as the background so we have a choice of whether or not to use additional sources of light. If we decide to use additional light, we must be aware not to let the light spill into the background and change the exposure. Our strobe light will likely only spill onto a portion of the background thus changing the exposure for only a portion of the background. We must also be aware to turn down the power of the strobe so it does not overexpose the subject with regards to the background. The answer to the title question then becomes, "Enough light to match the ambient exposure" because we are trying to preserve the background with ambient light.

These are just a few examples on how you would utilize the ambient light to your advantage. Obviously the choice to add light sources is a luxurious option to have when you're shooting with ambient light and gives you a lot of advantages to create different looks and outcomes!

1 comment: