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For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens. For a converging lens (for example a convex lens), the focal length is positive and is the distance at which a beam of collimated light will be focused to a single spot.
18 Σεπ 2023 · Focal Length Definition. Without getting into an in-depth physics discussion, the focal length of a lens is an optical property of the lens. The exact definition is: Focal length measures the distance, in millimeters, between the “nodal point” of the lens and the camera’s sensor.
The front focal distance of an objective is the distance between the front surface of the objective (the vertex point of the first lens) and its front focal point. The back focal distance is the distance between the vertex of the last lens and the back focal point.
Focal distance is the distance between the subject you are focusing to the camera sensor. Lenses that can work at close focal distances have higher magnification (or reproduction ratios) relative to lenses that need you to stay far from the subject.
Learn how to understand focal length and field of view for imaging lenses through calculations, working distance, and examples at Edmund Optics.
Explore what is & how to use lens focal length (the optical distance from the point where the light meets inside the lens to the camera's sensor) with Adobe.
For a defocusing lens (Figure 1b), the focal length is the distance from the lens to the virtual focus (indicated by the dashed lines), taken as a negative value. Some authors use different sign conventions, however, in particularly concerning the front and back focal length (see below).
