Lenses Types of Lenses Principal Focus Ray Diagrams
- Slides: 31
Lenses
Types of Lenses Principal Focus Ray Diagrams Magnification Power of a lens
What is a lens? • An optical device • Which transmits and refracts light
Types of Lenses • Converging lens – a. k. a convex lens – thickest in the center and bends light inwards
• Parallel rays entering a converging lens leave and converge at one point
Types of Lenses • Diverging lens – a. k. a concave lens – thinnest at the center and spreads light out
• Parallel rays entering a diverging lens leave and spread out
Our main focus • Converging lens • Specifically, the double converging lens
Optical center • Center of a lens C Principal Axis
Principal focus • Point • where parallel rays converge
Focal Length Distance from center to focus Power of a lens = 1/f f C f
Ray Diagram • Uses arrows to represent light rays • Predicts the image formed by any optical device
Special Terms • Object –The source of light rays • Image –The result formed by converging light rays
Constructing a Ray Diagram • Ray 1: Parallel to the principal axis • Refracted through the principal focus f C f
Constructing a Ray Diagram • Ray 2: Passes through the optical center • Undeviated (for a thin lens) f C f
Constructing a Ray Diagram • Ray 3: Passes through the principal focus • Refracted parallel to the principal axis f C f
Again, again! f C f
Description of images formed • Real Image • Virtual Image
Real Image • Image formed by rays that actually pass through it • Can be produced on a screen
Real Image f C f
Virtual Image • Image formed by rays which seem to come from it but do not pass through it • Cannot be produced on a screen
Virtual Image f C f
Description of images formed • Upright • Inverted
Upright Image f C f
Inverted Image f C f
Description of images formed • Diminished • Magnified • Same size
Diminished Image f C f
Magnified Image f C f
Magnified Image f C f
Magnification, m • height of image ÷ height of object • Distance of image ÷ distance of object
Same Size Image 2 f f C f 2 f