- Abbe value
- A measure of a material’s dispersion. Higher values mean less color fringing.
- Lecture 1
- Chromatic aberration
- Color fringing caused by dispersion in a lens.
- Lecture 1
- Collimated light
- Light with parallel rays and zero vergence.
- Lecture 1
- Convergence
- Light coming together toward a point of focus. Measured in positive diopters.
- Lecture 1
- Critical angle
- The angle of incidence beyond which light going into a lower-index medium is totally internally reflected.
- Lecture 1
- Diopter (D)
- The unit of vergence and lens power: the reciprocal of a distance in meters.
- Lecture 1
- Dispersion
- The separation of white light into colors because the index of refraction varies with wavelength.
- Lecture 1
- Divergence
- Light spreading apart as it travels away from a point. Measured in negative diopters.
- Lecture 1
- Focal point
- The point where collimated light focuses (or appears to come from) after a lens. Every lens has two.
- Lecture 1
- High-index lens
- A lens made of a material with a high index of refraction, letting strong prescriptions be thinner and lighter.
- Lecture 1
- Index of refraction (n)
- The ratio of the speed of light in a vacuum to its speed in a medium: n = c/v.
- Lecture 1
- Lens power (P)
- The vergence a lens adds to light, in diopters: P = 1/f.
- Lecture 1
- Negative lens
- A diverging lens; collimated light appears to come from a virtual focal point to its left.
- Lecture 1
- Normal
- The line perpendicular to a surface at the point where light strikes it.
- Lecture 1
- Optical infinity
- 6 m (20 ft). Light from this distance or farther is treated as collimated in optometry.
- Lecture 1
- Point source
- An idealized, infinitely small source of light that radiates equally in all directions.
- Lecture 1
- Positive lens
- A converging lens; its focal point (for collimated light) is real and to its right.
- Lecture 1
- Reflection
- Light bouncing off a surface, leaving at the same angle (from the normal) at which it arrived.
- Lecture 1
- Refraction
- The bending of light as it passes from one medium into another.
- Lecture 1
- Snell’s Law
- n₁ sin θ₁ = n₂ sin θ₂. Predicts the angle of refraction.
- Lecture 1
- Vergence
- The amount light is converging or diverging at a location: 1 ÷ distance (m) to the point of origin or focus.
- Lecture 1