Define principal focus of Convex lens and that of a concave lens.
Definitions : Principle Focus and Focal length of a spherical lens - YouTube
What is Focal Length in Photography? - Focal Length Explained
Question Video: Defining the Focal Length of a Lens | Nagwa
What is Focal Length? (And Why it Matters in Photography)
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