The focal length is a fundamental characteristic of a camera lens and refers to the distance between the lens and the focal point where the light is converged onto the sensor or film. It is measured in millimeters (mm) and indicates the degree of magnification of the image. The greater the focal length, the narrower the field of view, and the closer the subject appears. A short focal length (wide-angle lens) captures a wide portion of the scene and creates a sense of openness and space. A long focal length (telephoto lens) can make the subject appear closer and can create a compression of depth in the image.

The focal length also affects the depth of field. A lens with a short focal length (wide-angle lens) has a larger depth of field, ensuring that multiple layers of the image are in focus. A lens with a long focal length (telephoto lens) has a shallower depth of field, creating a blurred background known as the bokeh effect.

The focal length is an important factor in choosing the right lens for a specific task or style of photography. For example, wide-angle lenses are ideal for landscape or architectural photography, while telephoto lenses are better suited for sports or wildlife photography.

Overall, the focal length is a crucial factor in the composition and expressiveness of photos, and it is important to consider it when selecting the right lens for a specific task or style of photography.