The term "135mm" typically refers to a focal length used in photography. It indicates the distance in millimeters from the lens to the image sensor when the lens is focused at infinity. A 135mm lens is often used for portrait photography, as it allows for a flattering perspective and good subject isolation due to its ability to create a shallow depth of field. In addition to photography, "135mm" can also refer to a specific film format. The 135 film format, also known as 35mm film, is a popular type of film used in cameras. It is widely recognized for its versatility and quality, making it a standard choice for both amateur and professional photographers.