Keep a Natural Light Look in the Studio
In order to create a natural-appearing light in the studio for close-up and macro photography, you need both a key light and a fill light. The key light determines how shadows are cast in a scene, and the fill light determines how dark those shadows are.
In the natural world the sun provides directional light while the open shade (or any sunlight that’s bounced, reflected, or scattered) provides an ambient light. These two work together to create a key light and a fill light.
Creating a fill light to control detail in shadows
After you’ve analyzed your subject and scene and positioned your key light to create the shadows and highlights you want, set up a fill light to control how much detail shows in the shadows.
You can create a fill light with a second flash positioned very close to the camera. Ring flashes work well as fill lights, because they tend to create flat or nondirectional lighting. Another option is to use a fill card — any reflective surface that you can position to catch light from the key light and bounce it into the shadow areas of a scene.
The trick to using a fill light successfully is positioning it so that it casts a minimum amount of shadows in your scene; the closer the light source is to the scene, the better. A proper fill light works to fill in shadows with light, not to create shadows of its own.
Achieving that natural look with artificial lights
Understanding the purpose of a key light and a fill light — and their relationship to one another — is the first step in creating natural-looking light. From there you simply have to analyze your particular scene and create lighting that makes sense for your message.
Keep in mind the following when creating your lighting setup:
The position of your key light relates to the time of day you’d like to create. If you want to mimic sunset lighting or dusk/dawn lighting, then position your key light low. To mimic cloudy lighting conditions, raise your key light up high above the subject.
The level of your fill light’s intensity in relation to that of the key light determines how dark your shadows appear. If you’re attempting to mimic a bright sunny day, then your shadows should be exposed about three stops darker than your highlights.
To mimic cloudy lighting conditions or dusk/dawn lighting, you can raise the level of your fill light’s intensity so your shadows expose at about one stop darker than your highlights.
The quality of your key light determines how hard or soft your shadows appear. Remember that direct sun is a hard light source. Cloudy light is soft, and dusk and dawn provide varying levels of softness, depending on how far beneath the horizon the sun is.