What does focal length measure in a camera lens?

• A. The distance in mm between your lens and the sensor recording the image.
• B. The size of the camera sensor
• C. The weight of the lens
• D. The length of the lens barrel

Answer: (A)

Focal length is the distance in millimeters from the lens’s optical center to the image sensor when the image is in focus. This number tells you how the lens projects light onto the sensor, which determines how wide the scene appears and how much the subject is magnified. A longer focal length makes distant subjects look bigger and narrows the field of view, while a shorter focal length captures a wider scene with less magnification. The sensor size doesn’t change the focal length itself, though it does affect the final framing you get. The other options describe things like sensor size, weight, or barrel length, which aren’t what focal length measures.