What does EFL refer to in optical modules?
EFL, or Effective Focal Length, refers to the distance between the center of the camera lens and the focal point. It is a key parameter in optical modules used to describe the lens characteristics in camera systems. A shorter effective focal length results in a wider field of view but may cause more noticeable image distortion. Conversely, a longer focal length yields a narrower field of view and allows for longer shooting distances.
The formula for calculating the focal length of a lens is as follows:
f = vD / V = hD / W
where:
- f represents the focal length of the lens,
- v denotes the height of the sensor's target surface,
- h indicates the width of the sensor's target surface,
- D is the distance between the subject and the lens (object distance),
- W is the width of the subject, and
- V is the height of the subject.
In practice, camera module manufacturers focus on the effective focal length, while users are often more concerned with the equivalent focal length. The equivalent focal length is relative to 35mm film cameras, which have become a standard reference. A full-frame 35mm film image has a sensor size of 36.0mm x 24.0mm and a diagonal length of 43.27mm.
To convert between the equivalent focal length and the effective focal length, the following formula can be used:
Equivalent focal length = effective focal length * crop factor
where the crop factor varies depending on the sensor size and is calculated as:
Crop factor = 43.27 / sensor diagonal length
EFL is a critical metric for evaluating the focusing performance of a lens assembly. Specifically, it influences the angle of view, aperture size, and depth of field. Shorter focal lengths provide a wider field of view and larger monitoring range but may introduce distortion. Longer focal lengths offer a narrower field of view and greater detail at a distance.
