Camera technology: the difference between focal length and angle of view.

The Difference Between Focal Length and Angle of View

Focal length and angle of view both play an important role, but they do not mean the same thing. While the angle of view results from the calculation of sensor size and focal length, the focal length itself is a fixed value. Generally, this cannot be changed but using a zoom lens allows you to make adjustments.

In this article you can find out more about focal length and angle of view in more detail and how they are linked. We will also explain the differences of the two terms.

Focal Length in Photography

The focal length is the distance from the focus in the lens to the sensor in the camera. The focus is the sharpest point of the subject which needs to be photographed, while the lens in the camera marks the point of view from which the photo is taken. This distance is specified in millimetres (mm) and thus represents the unit of measurement for the focal length. This distance in the lens is not always recognisable from the outside, so it is not possible to deduce the focal length of a lens from its size. This means that each lens is therefore labelled.

A zoom lens with a 24 to 105mm fixed focal length.

Only the lens determines the focal length of a photo. The camera itself or the sensor size are irrelevant for setting the focal length. You can decide which lens to use depending on the desired image effect. You will need to take into account the possible image section, the size of the image and the distance from the subject.

There are lenses with fixed focal lengths and zoom lenses. When using fixed focal lengths, the lens must be changed in order to change the focal length. Zoom lenses, on the other hand, offer a range of focal lengths and can therefore be adjusted within a certain range without changing the lens. A wide-angle lens is recommended for large subjects that need to be completely photographed. These have focal lengths of less than 40mm. For long distances, telephoto lenses with focal lengths from 60 mm upwards are used.

The Angle of View in Photography

The angle of view results from the diagonal of the format used. This creates a link to the different sensor sizes. In rare cases, the angle of view is also determined by the height or width of the format instead of the diagonal.

The angle of view will change depending on the size of the sensor. If the sensor is small, as a result the angle will also be small. If the sensor is large, the corresponding angle also increases. A small angle of view does not fit as much subject matter as a large angle of view.

Comparing two different angles of view: a small angle of view.

The Link Between Focal Length and Angle of View

A focal length is a value, thus the angle of view changes with the sensor size. For example, if you have a full-frame sensor of 24×36 mm, a focal length of 28 mm corresponds to a wide-angle lens. The same focal length on a pocket camera with a much smaller sensor already corresponds to a telephoto lens.

The focal length can be changed by changing the lens or by using a zoom option on the lens. It is important to keep the following in mind: the greater the focal length, the smaller the angle of view and vice versa. The focal length is set by the photographer depending on the location and the size of the image section.

Depth of Field with Focal Length and Angle of View

The size of the image angle also determines the depth of field of an image. This indicates whether the background appears smaller or larger. Depth of field is represents the sharp sections in a photo. The closer the object is, the smaller the focal plane. This means that the larger the angle of view and the smaller the focal length, the shallower the depth of field. As long as the same sensor is used, the depth of field is only influenced by the focal length. The type of sensor can only be varied by using a different camera. If a camera with a larger or smaller sensor is used, the link between the depth of field and focal length will change. The image angle is compressed or stretched. If the camera and the size of the sensor has been changed, the focal length must be increased with a larger sensor in order to obtain the same angle of view.

The effect of a shallow depth of field: the subject in the foreground is sharp, whereas the background is blurred.

A longer focal length results in a shallower depth of field. To achieve the same depth of field with different focal lengths, the aperture setting must be changed. The aperture is the opening width of the entrance pupil. It controls the desired incidence of light. In order to achieve a high depth of field, the aperture must be closed further for lenses with short focal lengths than for a lens with long focal lengths. The more the aperture is closed, the greater the depth of field.

A camera's aperture.

Conclusion: the Difference and Link Between Focal Length and Angle of View

The difference between focal length and angle of view depends on how they are used. Both values are inter-dependent and interrelated. The focal length is a value that is determined by the lens. With zoom lenses, however, it can be changed within a specified range.

The angle of view depends on both the focal length and the sensor size. The sensor of a camera is a fixed component. Its size can only be influenced by changing the camera. The smaller the sensor, the smaller the angle of view.



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