Shadows are as important to a studio photographer as light. Shadows and their characteristics affect a photo signifigantly. In fact, everything you do to change the way light falls onto your subject will also affect the shadows you produce.
Since photos are limited to being two dimensional, we use shadows to illustrate depth and dimension. Portraits without shadows, for example, will often seem flat and lifeless. This is why portrait photographers will go to great length to get their light source away from the camera position (light coming from the camera position will not cast attractive shadows, i.e. on-camera flash).
Shadows and their quality determine the amount of detail that is recorded with the camera. For example, a small or directional light casts hard shadows on even the smallest surface irregularity which helps show texture. On the contrary, larger diffused light sources reveal less texture having softer shadows.
The edge of the shadow reveals the most about the character of the light used. Changing the placement of the light source and its size will allow you to control the types of shadows you produce. Using a large light source relative to the subject will produce a softer shadow edge as will bringing your light source closer to the subject. Diffusion added to a light source (in the form of a diffusion panel, softbox or an umbrella) will make the light more scattered causing the light to “wrap” around the object, thus producing a softer shadow edge. This effect is most desirable when you are not emphasizing surface texture or when photographing people.
Using smaller light sources or keeping them farther away will cause the shadow edge to appear hard. The hard edges produce a dramatic effect which can be quite useful for emphasizing the texture of an object. Harsh shadows on the human face are not typically considered pleasing and are reserved for special effects in most cases. An on-camera flash that is not diffused will typically create this type of hard light, as will an undiffused studio strobe or hot light.
The relationship between the brightness of the shadows and the highlights of a scene is known as lighting ratio. This will also affect the overall contrast of the scene and thus the “feel” of the photo. The ratio has more to do with quantity of light in the shadows rather than the quality of the shadows, so this will be addressed in a separate article.