A Field depth (DoF) indicates the sharpening area, before and after, the focus point in the image. This parameter varies according to the lens aperture and focal length. You can use it for creative purposes, such as generating photos with a blurred background (bokeh effect).
Factors that change the depth of field
When a camera lens focuses on a subject (object, person, animal or scene), there is space in front of and behind that point that remains sharp in the image. The extent of this entire area is recognized as depth of field, and it can be:
- Wide or deep depth of field: if the extension is large to the point that there is sharpness between distant elements;
- Shallow or narrow depth: if the length is short, resulting in more blur in the background and in front of the subject.
Below, we explain how lens aperture, focal length, object distance, and sensor size determine how wide the depth of field is.
lens aperture
The lens aperture defines the amount of light that enters the camera through the diaphragm. The larger the lens opening, the smaller the depth of field of the image..
On a lens with an f/1.4 aperture, the diameter is much larger than an f/8.0 aperture, for example. The larger the diameter, the greater the amount of light captured, so that only what is close to the camera will be recorded in focus.
Therefore, a lens with an f/1.4 aperture has a shallower depth of field than one with an f/8.0 aperture.
Large apertures are ideal for selfies with a blurred background (bokeh effect). Smaller apertures are suitable for landscapes, when you are not interested in blurring the background.
Focal distance
The focal length (focal length) defines the size of the field of view captured by the lens. The longer the focal length, the smaller the depth of field..
Each type of lens has a specific focal length. In fixed lenses, this parameter does not change. In zoom lenses, the focal length can be adjusted within minimum and maximum limits.
If we take a wide-angle lens as an example, the type that allows framing a large area of the scene, the focal length typically reaches 35 mm. A telephoto zoom lens has a focal length greater than 100mm.
Between both types, the telephoto lens has a more blurred background, as its focal length is greater. Just note that in photos of birds taken from afar, with zoom applied, the background of the image is often not in focus behind the animal.
object distance
The closer the subject is to the camera, the shallower the depth of field.. This means that if an object is 1 meter from the lens, its area of sharpness will be smaller than if the distance were 10 meters.
The decrease in depth of field is easily noticeable in macro photography, a category that expands the view of very small subjects, such as insects and flowers. In such images, the sharp area decreases in size as the subject gets closer to the lens.
In some situations, the sharp area is so small that it’s easy to miss it. One solution to this problem is to use the camera’s manual focus instead of autofocus (autofocus).
The effect of distance on depth of field is related to the circles of confusion, which indicate the level of sharpness. The smaller the circle, the sharper the image. However, the circle of confusion becomes larger as the subject moves away from the focus plane.
sensor size
Digital cameras bring a sensor that captures the brightness of the scene for the image to be registered. In general, the smaller the size of the image sensor, the greater the depth of field.
Thus, a camera with a full frame sensor (full size) tends to have narrower depth compared to an APS-C sensor (smaller) using the same lens.
Focal length and lens aperture adjustments help adapt depth of field when using different sized sensors. The adjustment of the distance in relation to the object to be photographed is also important, as it allows the photographer to arrive at an acceptable circle of confusion for each circumstance.
Practical examples
The lens aperture, focal length and distance to the subject are parameters that can be adjusted according to the intention of the photo. Below are some recommendations for three common circumstances.
Landscape and architecture photography
Ultrawide lenses are best suited for shooting landscapes as well as indoors for architectural or interior design purposes. By offering a wider angle of view, this type of lens allows framing large areas of the scene.
It is also recommended to close the camera’s iris until the depth of field reaches the desired sharpness. For this, the tip is to use the hyperfocal distance, a technique that maximizes the depth of field from the point of focus.
portraits
For portraits of people, animals or objects, it is recommended that the lens has a low f-stop number (larger aperture), in order to obtain a smaller depth of field. This will blur the background to make the subject stand out.
This type of adjustment can easily be applied to a DSLR or mirrorless camera. On smartphones, the tip is to use portrait mode, which triggers the cell phone’s depth sensor to generate the blur. In devices without this component, the adjustment is made by software.
sports photography
The telephoto lens is often used for sports shots or athletes in action. One of the reasons for this is the great distance that usually exists between the camera and the athlete. Another is the longer focal length of this type of lens, which allows you to highlight the athlete by leaving most of the scene out of focus.
It’s also important that the shutter speed is fast to prevent the athlete’s quick movements appearing in the image as blur.
