For several reasons, backlighting (and even side-lighting, as in landscape photography) is a better situation to work with than front lighting. Front lighting tends to make a subject/scene look flat and bland, which may not be an ideal way to handle a portrait lighting session. Front lighting is required when you need a high-key image. But that is often achieved by using multiple lights, not just one.
Backlighting, on the other hand, is desirable when you are attempting to recreate depth and dimension in your images. Though for depth and dimension, you also need something extra, illumination from the sides. Simple backlighting will allow you to achieve what is referred to as rim lighting effects in photography.
Rim lighting is a hint of light around the subject’s head and shoulders. That, in effect, separates the subject from the background and creates a sense of depth and dimension. At that point, you need a reflector to throw back some light from the side, and you will have a much better image.
Position of the key light
The light source should be off the lens axis to shoot backlit images to avoid ghosting and flares. Photographers deliberately try to induce flares in the picture, which looks good too, when done correctly! Another good reason you would want to avoid having the sun or the light source away from the frame is that it can throw the metering system haywire.
You can also position the sun directly behind the subject and then use the metering mode, as discussed in the subsequent para, to expose correctly for the subject.
Position of the subject
Your subject should be facing you and not the light source. Have her stand at a slight angle so that you have a subtle rim light effect on her head and shoulders.
Use the partial metering mode to meter for the face only. The sampling size for metering is slightly bigger than in spot metering. This mode considers the center part of the frame surrounding the active AF point and disregards the rest. This is what you want because the rest of the frame will be too bright than the face anyways. Unfortunately, Nikon cameras don’t come with partial metering mode. Canon does. Nikon users can use the spot metering mode and slightly bump up the exposure so that the face is properly illuminated.
These are, however, all subjective depending on the light intensity and the reflectance of the immediate surroundings. These are all liable to change and should be used only as a guideline, not as a rule.
Experiment with the position of the subject and the key light to make better, more compelling exposures.
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