Optics: Lenses and Light Behavior

Course Description

• The course aims to teach students about unifocal and multifocal lenses.
• It will provide a foundation for physical and geometrical optics.

List of Topics

• Introduction to Ophthalmic Optics: 3 contact hours
• Refraction, Reflection, and Prism: 3 contact hours
• Refractive Power and Lenses: 3 contact hours
• Spherocylindrical Lenses: 3 contact hours
• The Eye and Refractive Errors: 3 contact hours
• Lens Form and Thickness: 3 contact hours
• Aberrations and Lens Design: 3 contact hours
• Ophthalmic Prisms: 6 contact hours

Assessment Tasks

• 1st Quiz: 4th week, 10%
• Midterm Exam: 7th week, 20%
• 2nd Quiz: 9th week, 10%
• Presentation: 10th week, 10%
• Homework: Every 3 weeks, 10%
• 2-hour Written Exam: 12th week, 40%

Reflection

• Reflection occurs at all interfaces, to some degree.
• Light may be reflected or absorbed.
• The incident ray, reflected ray, and the normal all lie in the same plane.
• The angle of incidence equals the angle of reflection.

Reflection at Spherical Mirrors

• Concave mirrors are thicker in the middle
• Convex mirrors are thinner in the middle

Refraction

• Refraction is the bending of light when passing between transparent media with different densities.
• The speed of light changes as it moves from one medium to another.
• A pencil in water appears bent due to this effect.

Light Refraction

• Light changes direction when moving from one transparent medium to another with different optical density.
• Higher density means slower light and a higher refractive index.

Snell's Law

• Snell's Law relates angles of incidence and refraction when light passes from a rarer to a denser medium by refractive index.
• n₁sinθ₁ = n₂sinθ₂
• θ₁ is the angle of incidence
• θ₂ is the angle of refraction
• n₁ is the refractive index of the rarer medium
• n₂ is the refractive index of the denser medium

Refraction of Light

• Light slows down in denser media (like glass).
• Light bends toward the normal when entering a denser medium.
• Light bends away from the normal when entering a rarer medium.

Lenses

• Lenses are transmissive devices, bending or focusing light.
• There are different types of lenses: convex and concave.
• Different types of lenses have different focal lengths and powers.

What is a Lens?

• A lens is a transmissive device that disperses or focuses light by refraction.

Basic Types of Lenses

• Convex (converging) lenses: Thicker in the middle, curving outward.
• Concave (diverging) lenses: Thicker at the edges, curving inward.

What is the main difference between a lens and a mirror?

• Light rays pass through a lens, and are refracted.
• Light rays are reflected by a mirror.

Type of Image

• Mirrors create images by reflection.
• Lenses create images by refraction.
• Lenses are classified as thick or thin, thin lenses are considered as lines.

Types of Lenses

• Convex Lenses (Converging):
  • Double-convex
  • Plano-convex
  • Concavo-convex
• Concave Lenses (Diverging):
  • Double-concave
  • Plano-concave
  • Convexo-concave

Representing Thin Lenses

• In diagrams, thin lenses are often represented by arrows.

Lenses - Summary

• Convex lenses converge light rays, concave lenses diverge light rays.

Diverging Lens

• Produces only virtual, erect, and reduced images.
• Focal point is virtual.

Converging Lens

• Can form real and virtual images.
• Real images are inverted and can be enlarged or reduced.
• Virtual images are upright and can be enlarged.

Focal Length

• The focal length of a lens is the distance from the center of the lens to the focal point.

Ray Diagrams for Convex Lenses

• A parallel ray refracts through the focal point.
• A ray through the center of the lens continues straight.
• A ray through the focal point refracts parallel to the principal axis.

Case Studies for Convex Lenses

• There are six cases to be studied regarding the location of the object relative to the focal length.

Summary for Convex Lens

• Case-1: Object at infinity - Image is a point at focus, no image is formed.
• Case-2: Object beyond 2F- Image is between F and 2F.
• Case-3: Object at 2F - Image is at 2F.
• Case-4: Object between 2F and F- Image is beyond 2F.
• Case-5: Object at F- No image is formed.
• Case-6: Object within F - Image is virtual, upright, and magnified.

Concave Lenses

• Only one case needs to be examined for this lens.
• Images formed are always virtual, upright, and reduced.

Power of a Lens

• The ability of the lens to bend light.
• Measured in Diopters.
• The inverse of focal length(m)

Lens-Maker's Equation

• Equation used to calculate the focal length of a lens based on the refractive index of the lens material and the radii of curvature of its surfaces.
• 1/f = (n-1)(1/R₁ - 1/R₂)

Test your understanding of optics, focusing on lenses and their behavior with light. This quiz covers concepts such as refractive index, image characteristics, and geometric optics. Perfect for students studying physics or preparing for exams!