Optics Flashcards
What is High Order Aberrations?
A distortion acquired by a wavefront of light when it passes through an eye with irregularities of its refractive components, such as: tear film, cornea, aqueous humour, crystalline lens and vitreous humour.
Electromagnetic Spectrum
The range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.
Visible Light
Electromagnetic radiation at wavelengths which the human eye can see.
We perceive this radiation as colours ranging from:
- Red = Longer wavelengths - 700nm
- Violet = Shorter wavelengths - 400nm
What does the Electromagnetic Spectrum consist of?
1) Radio Waves
2) MicroWaves
3) Infrared
4) Visible Light
5) Ultraviolet
6) X-ray
7) Gamma Ray
Electromagnetic Radiation
Refers to the waves of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy, in which electric and magnetic fields vary simultaneously.
Frequency
cycles per second - Hertz.
Wavelength
metres
Energy
electron Volts
Radio Waves ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ Gamma Rays
Long Wavelength
↓
Short Wavelength
Lower Frequency
↓
Higher Frequency
Lower Energy
↓
Higher Energy
Lightray
A ray is an idealised model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow.
Incident ray
An incident ray is a ray of light that strikes a surface. The angle between this ray and the perpendicular/normal of the surface is the angle of incidence.
What order does light travel through the Eye?
Conjunctiva ↓ Cornea ↓ Aqueous humour ↓ Lens ↓ Vitreous humour ↓ Retina/ macula – fovea
What are the stages in Visual Process?
1) Normal stimulus to vision i.e. light
2) The formation of an image when the optical image falls on the retina
3) Photochemical reaction between light falling on the retina and chemical light-absorbing substances within it.
4) Rod reaction is mediated by the substance known as visual purple
What are the Retinal Photoreceptors?
Rods
Cones
Rods
Rods become fully active at Low scotopic levels of illuminance (dim light)
Cones
Cones become fully active at High photopic levels of illuminance (bright light)
What is the ratio of Rods:Cones in the Human Eye?
7million CONES and 120million RODS
Distribution of Cones
Fovea Centralis is densely packed with cones only, there are virtually no rods present.
The distribution of cones decreases from the Central pit to the Periphery at low density.
Distribution of Rods
Rods are concentrated at the outer edges of the Retina and are used in Peripheral Vision.
Sensitivity of Photoreceptors
Rod cells are more sensitive than Cone cell and are almost entirely responsible for Night Vision.
How is the Macula responsible for Critical Vision?
The High Spatial Density of Cones along with the absence of blood vessels at the Fovea accounts for the High Visual Acuity capability at the fovea.
Basic Sign Convention
Concave
Convex
Practical Implication for Concave lenses?
If you have Myopia or Nearsightedness, you would use Diverging, Concave lenses to shift the focus of your eye lens backwards so that it can focus on the Retina.
Practical Implication for Convex lenses?
If you have Hypermetropia or Farsightedness, you would use Converging, Convex lenses to shift the focus of your eye lens closer so that it can focus on the Retina.