The depth of field in an image is the distance between the nearest and the furthest objects that are in focus. When the depth of field is shallow, this distance is small and means that the foreground and background are likely to be very blurry if your focal point is the centre of the image. A deeper depth of field has more of the image in focus.
Portraits where the background is blurry is an example of shallow depth of field, whereas landscapes tend to have a deeper depth of field, so that both the background and foreground are in focus.
Depth of field is controlled by the f-stops on the camera. F-stops also control the volume of light entering the camera. The smaller the f-stop, the more light, and it will also produce a more shallow depth of field.
To obtain an image that is almost entirely in focus, larger f-stops are needed, and as the volume of light is more limited, the aperture of the lens will need to be open for longer to compensate. There is a greater chance of camera shake in that time, hence why landscape photographers almost always use a tripod.
It is the lens of the camera that determines the range of f-stops you have available to you, for example on the 16-85mm lens I use, the largest f-stop is 3.5. I can get a reasonably shallow depth of field with this.
Play with Depth of Field and get to know those F-stops! Try taking a photo of the same subject using different depth of fields. As those numbers get larger e.g. f22, the shutter speed with decrease, so using a tripod is advisable. However, supporting the camera on a wall, or with a cushion are ways to overcome not having a tripod.
Not all cameras have f-stops, so if you use your smart phone camera, then check out apps where you can apply depth of field after the photograph is taken. Some suggestions are:
iOs – AfterFocus, Big Lens, Tadaa SLR, Snapseed and Filterstorm Neue
Android – Lytro, Google Camera
I’ve not tried any of these apps, so can’t vouch for how well they work.
I worked with a set of three glasses, making use of the ‘rule of threes’ compositional technique. I shifted the focus between the three glasses, using as wide an aperture as possible given the low natural light I was working with. I’ve chosen this as my pic of the week, it focuses on the front glass with a reasonably shallow depth of field. However, you’ll notice that there is a strong colour cast in this photo. It looks like I took it an hour before dawn in the ‘blue hour’ rather than closer to midday. This is a feature of shooting in natural light in winter. The colour temperature remains cold. This is adjustable and we’ll talk about how in the next challenge. Additionally, there are strong reflections in the glass which can also be overcome. We’ll deal with this in a later challenge too.