Focal length, in the context of photography and optics, is the distance between the center of a camera lens (or a curved mirror) and the focal point (or image sensor) when the lens is focused at infinity. It is typically measured in millimeters (mm) and is an essential factor in determining the angle of view, magnification, and depth of field in the resulting images.

Different focal lengths produce distinct visual characteristics:

• Short focal lengths (wide-angle lenses):

  These lenses have focal lengths typically between 10mm and 35mm. They provide a wider field of view, allowing more of the scene to be captured in a single frame. Wide-angle lenses are often used for landscapes, architecture, and interior photography, as they emphasize the foreground and create a sense of depth.

• Medium focal lengths (normal lenses):

  With focal lengths ranging from around 35mm to 70mm, these lenses produce images that closely resemble what the human eye perceives. They are suitable for a wide range of subjects, including portraits, street photography, and events.

• Long focal lengths (telephoto lenses):

  Ranging from 70mm to upwards of 400mm or more, telephoto lenses enable the photographer to capture distant subjects, effectively magnifying the scene. They are commonly used for wildlife, sports, and other situations where the photographer cannot get close to the subject. Telephoto lenses compress the foreground and background, resulting in a flattened perspective.

In summary, the focal length of a lens plays a crucial role in determining the composition and perspective of a photograph, and choosing the right focal length for a specific shot is essential for achieving the desired results.