For the most part, portraiture focuses on depth of field, the of photo that is sharp and the part of the photo that isn’t. The look and feel of the photograph is going to greatly vary depending on how you present the subject to the viewer based on depth of field. Using a shallow depth of field, where only part of the photo is in focus and sharp, allows the concentration of the viewer to know exactly what you want them to pay attention to. When deciding how to focus on depth of field there are three things that determine how your photo will turn out; aperture, distance from the subject, and focal length.
By far and most common way that people adjust depth of field is through lens aperture. For a shallow depth of field, where the subject is in focus and the background is blurry, we choose a large aperture setting (small number) such as f/2.8 or f/1.4. The larger your aperture the more shallow your depth of field will be. In order to create a deep depth of field, where more of the photo is going to be in focus, use a small aperture (large number) such as f/8 or f/16.
That’s all great but what do you do if you don’t own a lens that allows for a large enough aperture to get the shallow depth of field desired? Are you just stuck getting images with deeper depths of fields? NO! In addition to using aperture you can use distance to create a shallow depth of field. Depth of field has a 1/3-2/3 ratio, meaning that when you take a photo 1/3 of your depth of field comes before your subject and 2/3 of your depth of field comes after your subject. So the further your subject is from the background the shallower your depth of field will be. Along those same lines you can create a much shallow depth of field by moving closer you your subject, extending that 2/3 ratio.
In addition to aperture and distance from your subject, depth of field is also determined greatly by the focal length of the lens you use. It is similar to distance to your subject but if you stand back and zoom in on your subject you will get a much more shallow depth of field than if you were just standing closer in using a wider focal length. Keep in mind, however, that the best focal length to use when shooting portraits is between 50mm and 135mm to avoid distortion to your subjects.
When going for a shallow depth of field it is essential that your focus is spot on. As a general rule, especially when working with a shallow depth of field, you want to focus on the eyes. When we look at photographs the first thing we look at is the eye of the person in the photograph. When working with extremely shallow depths of fields if your focus is off even a little it will throw off the entire look and quality of the photo.
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