In this post I will be discussing focus and depth of field regarding studio portraiture.
There is only one Focal Point (Principle Focus or Focus) when photographing a subject, but within a certain distance in front and behind the focal point there is a distance of reasonably sharp focus. This is referred to as depth of field.
The range of depth of field depends on three factors, the distance the camera is from the subject, the aperture being used, and the focal length of the lens. The closer the camera is to the subject the smaller the depth of field and the greater the distance the greater the depth of field. Also, the wider the aperture on the lens, the smaller the depth of field and the smaller the aperture the greater the depth of field. Like wise, the longer the focal length of a lens, the smaller depth of field and the smaller the focal length (wide angled the lens) the greater the depth of field.
All this was very apparent on older SLR cameras, when there was depth of field scales on the lens, but unfortunately on modern cameras, they are no longer included.
Also, depth of field isn’t an equal distance from the focal point. Roughly the depth of field is one third in front and two thirds behind the focal point. See example below.
In the first photograph, the camera is focused on the fourth post into the photograph and is set at a wide aperture. Only that post is in sharp focus. As the aperture is reduced, more posts come into focus, but not at an equal distance. There are less posts in front in focus as there are behind.
Focusing The Camera For Portraiture
When focusing the camera on a portrait subject, you should always focus on the eyes. The eyes should always be as sharp as possible, but the rest of the face can be soft. The effect can be helped along a bit in post by sharping the eyes while leaving the rest of the face unsharpened. Later, I will be posting a tutorial about smart sharpening with PhotoShop.
The Camera Technique For Focusing On A Subject
This is a technique that was taught to me at university. Set the camera to Single-Point AF. This will set a single focusing point in the camera viewfinder. While on autofocus, aim the focusing point on one of the subjects eyes and then half press the shutter realise. Then compose the photograph and then fully press the realise button taking the photograph. Your routine will be as follows:
Focus, compose. Focus, compose. Focus compose…..
Headshot or Head and Shoulders
While shooting headshots, I use a focal length of 120mm to avoid perspective distortion (See tutorial on perspective distortion). To gain enough depth of field to focus the whole of the subjects head, I use an aperture of f8.
While photographing couples or groups, use a small aperture and take into consideration the 1/3 in front and 2/3s behind rule. Usually focus on the person or people at the front.
I hope you found this tutorial helpful.