Biomedical Physics Course Ch. 6: Optics and Vision

Biomedical Physics Course (7108101)

• Course name: Biomedical Physics Course
• Course code: (7108101)
• University: An-Najah National University
• Department: Department of Biophysics and Medical Imaging

Ch. 6: Optics and Vision

• Optics is the study of light and its interaction with matter.
• Vision is essential to perceiving the world.
• Visible light is the range of electromagnetic radiation that the human eye can see, approximately 380 nm to 750 nm.
• Light reflects off objects, allowing us to see them.

Introduction

• Vision is the most evocative sense, allowing us to perceive the world at long distances.
• We experience the world through multiple senses.

Sec 6.1: Geometric Optics

• This section covers geometric optics principles.
• Information about geometric optics is included in these notes.

Sec 6.2: Eye and Vision

• Covers how the eye functions in light.
• Information about eye function is included in these notes.

Vision and Light

• Light is essential for vision.
• Understanding light's behavior is important to understand vision.
• Light is visible electromagnetic radiation.
• Light reflects off objects, allowing us to see.

Sec 6.1: Geometric Optics

• This section focuses on geometric optics which provides a more detailed insight.

Reflection

• Reflection is a change in the direction of a light ray when it hits a boundary between two surfaces, turning back without transmitting through.
• The reflected light leaves the surface at the same angle as the incident light making the "law of reflection".
• Diffuse reflection occurs on rough surfaces, causing light to scatter.
• Specular reflection happens on smooth surfaces, creating clear reflections.

Refraction

• Refraction is a change in the direction of light rays when passing between two different mediums due to a change in wave speed.
• The speed of light changes when moving between different media.
• The wavelength of light changes with refraction but the frequency remains constant.
• Light from an object underwater appears closer to the surface than it actually is due to refraction.

Refractive Index

• Refractive index (n) is a ratio of the speed of light in a vacuum (c) to the speed of light through a material (v).
• It is denoted by n = c/v
• Snell's law describes how light bends when entering a different medium.

Image Production

• An image is a reproduction of an object by light, either by refraction or reflection.
• Images are not always identical to the original object (e.g., can be larger, smaller or inverted).
• Some images appear on a surface, others do not show.

Plane Mirror

• A plane mirror is a flat reflective surface.
• Images produced by plane mirrors are virtual: light rays don't actually come from the image.
• Images are upright and the same shape and size as the object.
• The image and object are equidistant from the mirror.

Converging and Diverging in spherical mirrors and lenses

• Mirrors create images by converging or diverging reflected light.
• Lenses create images by converging or diverging refracted light.
• Different types of mirrors (convex and concave) and lenses (double convex and double concave) have different effects on light.

Lenses

• Lenses are pieces of transparent materials used to bend light rays.
• Double concave lenses diverge light rays.
• Double convex lenses converge light rays.
  • Diverging lenses make images that are smaller and upright.
  • Converging lenses make images that may be smaller or larger, and inverted or upright.

Image Types

• Images result from the gathering of proceeding light rays (refracted or reflected).
• Real images are formed by converging light rays, can be projected on a screen, and are always inverted.
• Virtual images are formed by diverging light rays and cannot be projected on a screen; they appear to be behind the lens or mirror, and are sometimes upright.

Ray Diagram

• Crucial for optical system analysis, involving:
  • Focal length (distance where parallel rays converge/diverge).
  • Object height
  • Image height
  • Object distance (from the optical center)
  • Image distance

The mirror or thin lenses equation

• Mathematical relationship between the object’s location and the corresponding image's location.
• Equation provides calculations for various aspects of mirrors and lenses.
  • f: focal length.
  • di: image distance.
  • hi: image height.
  • do: object distance.

Lateral Magnification

• Ratio of image height to object height.
• M = (image height)/(object height)
• Also representable by negative ratio of image to object distance.
• A negative magnification value indicates an inverted image.

Lens Power

• Measure of a lens's strength, expressed as P = 1/f.
• Units of lens optical power are diopters (D).
• Long focal length indicates a weaker lens.

Questions about lenses

• Students are expected to determine the type and optical power of a lens.

Homework Problem (H.W.1)

• Determine object distance and image type for an inverted, magnified image formed by a double convex lens.

Explore the principles of optics and the mechanics of vision in this comprehensive quiz based on Chapter 6 of the Biomedical Physics Course. Delve into topics such as geometric optics, the function of the eye, and the nature of visible light. Enhance your understanding of how we perceive the world around us through light.