4 - Grover - Visual Optics Flashcards
Refraction
Refractive Index
Bending of light caused by change of velocity of light as it crosses interface between two substances
Refractive Index = Speed in Air / Speed in Substance
Convex Lens
Convex Lens converge parallel light rays
At center of lens, light not bend, angle of incidence increases moving out, leads to greater refracting
- - -
Bends light to single point behind lens
Concave Lens
Concave lens diverge parallel light rays
Center of lens not bent, increasing angle of incident towards edge, greater refraction
- - -
Concave lens bens light away from a single point
Cylindrical Lens
Concave or Convex in only one axis
Light refracted towards or away from a line, not a point
Cylindrical Lenses combined at right angles?
Have same focuses effect as one spherical lens
Focal Length
How does it change with distance of source?
Convexity impact on Focal Length?
Distance behind convex lens at which light rays converge
- - -
The closer th source, the greater the focal length
Refractive Power: Diopter
Diopter = 1 m / Focal Length (m)
+1 Diopter = 1 m Focal Lenth
+2 Diopter = 0.5 m Focal Length
- 1 Diopter diverges light equal to which Concave focuses (focal point on same side as source)
How is refractive power “neutralized”
Combinding Concave and Convex lenses with equal focal strengths (diopters)
Ex. +1 Concave and -1 Convex
Refractive Power - Cylindrical Lenses
Focal Line - Horizontal = Axis of 0 degrees
Focal Line - Vertical = Axis of 90 degrees
Refractive Interfaces of Eye
Air - Surface of Cornea
Back of Cornea - Aqueous Humor
Aqueous Humor - Surface of Lens
Back of Lens - Vitreous Humor
Greatest Refractive Power in Eye?
2/3 Air and Cornea
1/3 Lens
Accommodation
Change in refractive power by changing curvature of lens
Range of Accommodation in Lens
20 d - 34 d
Only in young children, range decreases with age
Nature of Lens in Resting Conditions
Ligaments Tense = Lens Flat = Less Power
Nature of Lens in Contracted Conditions
When contracted ligaments are pulled anterior/medially, releasing tension, more convex = more power
Circular fibers function like a sphincter
Contracted = Relaxed Ligaments = More Convex = More Power