To me, the single most important element that determines the success of a photo is the light. Also important are composition, the subject, capturing the exact moment and the technical aspects of depth of field and focus. But of all these, dramatic and intriguing light reign supreme. I'd rather photograph an ordinary subject in great light than an amazing one in poor light. When all of the above aspects come together, shutter release bliss is the result.
The quality of the light is determined by its color, angle, direction and intensity. Sunrise and sunset provide warm colored light as does a yellow gel on a flash or light bounced off a gold reflector. Low angled light occurs early and late in the day as does artificial light kept low to the subject. The direction of light is important as it can either emphasize or flatten texture and shape. Front light suppresses texture while low angled light from the side emphasizes it. Soft light provides shadowless results and tends to wrap an even layer around the subject while intense and strong light creates high contrast situations.
Rim light provides a very specific quality of illumination. It outlines the subject in a halo of brightness determined by the direction and intensity of its source. It's often referred to as backlight. Depending on its strength and how it's augmented, the subject can fall into silhouette or detail on the shadow side can be brought out. The more simplified the background is, the more the subject is separated.
Getting a proper exposure can be a bit tricky, especially if the goal is to record detail on the shadow side of the subject. As a matter of fact, the exposure can be used to create a mood. Underexposure will place an emphasis on the shape of the subject and create a darker and more dramatic mood while brighter versions will be more open and airy. I strongly encourage you to evaluate the histogram to see where most of the pixels fall and adjust the exposure to match the mood you want to create.
If the goal is to reveal detail on the shadow side, it's necessary to augment the source of the rim light. The use of flash works well if the subject is close and the flash is powerful enough to throw the required amount of light back onto the subject. Reflectors also work well to bounce light. If you can work with an assistant who can do this for you, it makes your task easier. Gold reflectors bounce back warm light while silver ones work well to add lots of illumination even from a great distance. The color of the subject needs to be taken into account with regards to how much light is required to provide detail. The lighter the subject, the less bounce light is required. Conversely, a dark subject requires more.
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