optics - What is the actual significance of the focal point of a lens? - Physics Stack Exchange
Thin Lenses and Lens Systems
Principal focal length
Physics: Optics- Thick Lenses (6 of 56) The Effective Focal Length - YouTube
optics - The focal length of spherical mirrors - Physics Stack Exchange
Understanding Focal Length and Field of View | Edmund Optics
GCSE PHYSICS - What are Ray Diagrams? - What is the Focal Length of a Convex Lens? - What is the Focal Point? - What is the Principle Axis? - GCSE SCIENCE.
Focal Length of a Lens
Focal Length | Imaging the Universe - The University of Iowa