When shooting a portrait, especially a head and shoulders portrait (a.k.a. headshot), isolating the subject from the background is often a desirable outcome. The idea is that after we have selected a complementary background — one that doesn’t distract or take away from the subject — we should also seek to blur it as much as possible. This will further remove the background as a distraction, and by sheer contrast between subject sharpness vs. background softness, will more effectively focus the attention on the subject.
There are several tools to accomplish this, including lens selection (longer works best), aperture (wider apertures also work best, but keeping in mind what’s needed to ensure the subject’s features are sufficiently sharp), and reducing the distance between the camera and the subject also helps. But there’s another variable I often forget, as the following two photos, both shot with the same lens, same aperture, and roughly at the same distance between camera and subject demonstrate.
Headshot 1, Nikon D700 & 105 f2.0 DC @ f/4
The subject is sufficiently isolated from the background, but even at this fairly large aperture, the background isn’t as blurred as I wanted. I noticed this after taking a few shots, and asked my subject to move farther away from the background. Since we were shooting in open shade, I brought her to the edge of the shaded area, while keeping an eye on the lighting, which I wanted to maintain. With the subject farther from the background, I captured the next shot.
Both the background and the pose make for a different shot, and I was reminded once again to sufficiently separate my subject from the background in future shoots.