The distance between the optical centre of lens and the focal point is called :
Define focal length.
Lens Focal Length and F-stop | Digital Camera Know-Hows | Digital Camera | Digital AV | Support | Panasonic Global
How To Define the Focal Point of a Room | Pella Windows & Doors
Focal Length of a Lens
Understanding Your Camera: Revisiting Focal Length : Martin Pot - Photography Blog
Definition: Focal point; principle focus; point of interest - Photokonnexion
Lesson 4 Define the terms principal axis, focal point, focal length and linear magnification as applied to a converging (convex) lens. Define the power. - ppt download