EFL (Effective Focal Length), which refers to the effective focal length, is defined as the distance from the center of the lens to the focal point. In optical design, focal length is categorized into image-side focal length and object-side focal length. Specifically, EFL pertains to the image-side focal length, i.e., the distance from the image-side principal plane to the image-side focal point. As one of the critical parameters in optical system design, EFL significantly influences system performance. A focal length that is too short may result in an excessively wide field of view angle, leading to intensified distortion and challenges in controlling the exit angle of the chief ray. Conversely, a focal length that is excessively long can hinder compact system design and fail to meet practical application requirements due to an overly narrow field of view.
BFL (Back Focal Length), or optical back focal length, is defined as the distance from the rear surface of the last lens in an optical system to the image plane. As a key parameter in optical design, BFL directly impacts the overall system length and the accuracy of the rear focal length. Therefore, it must be carefully considered during system design.
FFL (Front Focal Length), or optical front focal length, represents the distance from the front surface of the first lens in the optical system to the object surface. It is important to note that FFL differs fundamentally from FBL (Flange Focal Length). The former denotes optical distance, while the latter refers to mechanical distance.
FBL (Flange Focal Length), or flange focal length, is defined as the distance from the last mechanical surface to the image surface of the lens group. In the design of camera and lens interfaces, FBL is a pivotal parameter that determines the precise position at which the lens is mounted on the camera.
In summary, these parameters are indispensable in the design of optical lenses. They not only directly influence lens performance and imaging quality but also profoundly affect the feasibility of system design.
Post time: Jun-06-2025