Eye & Optical Machines

NODE 01

The Human Eye

• The eye as an optical system.
• Cornea → Pupil → Lens → Retina → Brain.

NODE 02

Cornea

• Provides major part of optical power.
• Curved transparent surface, refraction.

NODE 03

Iris & Pupil

• Iris: controlling structure.
• Pupil: opening for light.
• Aperture control for bright/dim conditions.

NODE 04

Eye Lens

• Crystalline lens fine-tunes focusing.
• Changes curvature/focal length (Accommodation).

NODE 05

Accommodation

NEAR OBJTHICK LENS

FAR OBJTHIN LENS

• Ciliary muscles change lens shape.
• Eye is NOT a fixed-focus camera.

NODE 06

Retina

• Light-sensitive surface.
• Photoreceptors (Rods, Cones).
• Conversion to neural signals.

NODE 07

Real Image in Eye

• Forms real, INVERTED image on retina.
• Brain interprets the visual information to be upright.

NODE 08

Near & Far Point

NEAR~25cm

FAR~∞

• Near: closest distance for clear focus.
• Far: farthest without accommodation.

NODE 09

Defects of Vision

MYOPIAHYPERMETROPIAPRESBYOPIAASTIGMATISM

• Major school-level defects.
• Require optical correction.

NODE 10

Myopia

• Short-sightedness. Focus is in front of retina.
• Correction: Concave (diverging) lens.

NODE 11

Hypermetropia

• Long-sightedness. Focus is behind retina.
• Correction: Convex (converging) lens.

NODE 12

Presbyopia

AGE-RELATEDREDUCED
ACCOMMODATIONLENS CORRECTION

• Age-related reduction in accommodation.
• Difficulty with close work.

NODE 13

Astigmatism

• Different focusing power in different directions.
• Correction: Cylindrical/toric optical power.

NODE 14

Colour Vision

• Cones provide colour perception.
• Different spectral sensitivities to wavelengths.

NODE 15

Visual Acuity

E

F P

T O Z

• Ability to distinguish fine detail.
• Angular separation, resolution, contrast.

NODE 16

Angular Size

• Small object appears large if angular size increases.
• Foundation of magnifying instruments.

NODE 17

Ang Magnification

M =θ_INSTRUMENT / θ_EYE

• Apparent angular size with instrument / without instrument.
• Different from linear magnification.

NODE 18

Simple Magnifier

• Convex lens, object within focal length.
• Virtual, upright, enlarged image.

NODE 19

Magnifying Power

RELAXED: M = D/fNEAR PT: M = 1+D/f

• D = Near-point distance (usually 25cm).
• f = focal length.

NODE 20

Compound Micro

• First major optical machine.
• Object → Objective → Real Img → Eyepiece → Virtual Final Img.

NODE 21

Objective Lens

• Short focal length. Operates close to specimen.
• Forms real, inverted, magnified intermediate image.

NODE 22

Eyepiece Lens

• Acts as a simple magnifier.
• Enlarges angular appearance of intermediate image.

NODE 23

Micro Magnification

M_total= M_obj × M_eye

• Total angular magnification.
• Depends on f_o, f_e, tube length.

NODE 24

Micro Resolution

• Magnification isn't enough; resolution matters.
• Minimum resolvable separation. Diffraction limited.

NODE 25

Telescope

• Designed to observe distant objects.
• Distant Obj → Objective → Intermediate Img → Eyepiece.

NODE 26

Refracting Tele

• Uses lenses.
• Objective collects light. Eyepiece magnifies.

NODE 27

Astro Telescope

OBJECTIVELARGE f & A

EYEPIECESMALL f

• Objective: Large focal length, large aperture.
• Eyepiece: Small focal length.

NODE 28

Tele Ang Mag

• Normal adjustment: M = f_o / f_e.
• Magnitude tells angular enlargement.

NODE 29

Normal Adjustment

• Final image effectively at infinity.
• Minimizes accommodation for relaxed eye.

NODE 30

Tele Resolution

• Depends strongly on APERTURE.
• Diffraction limits distinguishing close sources.

NODE 31

Reflecting Tele

• Concave primary mirror, secondary mirror.
• Reduced chromatic aberration. Astronomy standard.

NODE 32

Refract vs Reflect

REFRACTLENS-BASED

REFLECTMIRROR-BASED

CHROM ABERAVOIDS CHROM

• Mirrors avoid chromatic aberration.
• Large mirrors easier to support than large lenses.

NODE 33

Aberrations

SPHERICALCHROMATICCOMAASTIGMATISM

• Real systems are not perfect.
• Beginning of optical engineering.

NODE 34

Spherical Aberr

• Rays through different portions don't converge to exactly same point.
• Solved with aspheric surfaces/multiple elements.

NODE 35

Chromatic Aberr

• Different wavelengths refract differently (Dispersion).
• Lens focuses colours at different distances.

NODE 36

Achromatic Lenses

• Combination of optical materials reduces chromatic aberration.
• Optical system design vs single lens.

NODE 37

Fibre Optics

• Core surrounded by cladding.
• Suitable refractive index relationship.

NODE 38

TIR in Fibres

• Guiding mechanism is Total Internal Reflection.
• n_core > n_cladding.

NODE 39

Fibre Structure

CORECLADDINGCOATING

• Light path within core.
• Guided modes (advanced preview).

NODE 40

Acceptance Angle

• Accepts light only within range of input angles.
• Acceptance cone.

NODE 41

Numerical Aperture

• NA = √(n₁² - n₂²).
• Describes fibre's light-collection capability.

NODE 42

Modes

SINGLE

MULTI

• Single-mode: one guided mode, long dist.
• Multimode: multiple propagation modes.

NODE 43

Fibre Attenuation

• Signal power decreases as light propagates.
• Absorption, scattering, bending losses.

NODE 44

Fibre Dispersion

• Modes/wavelengths arrive at diff times.
• Broadens pulses, limits bandwidth.

NODE 45

Fibre Comm

• Elec Data → Modulation → Fibre → Photodetector → Elec Signal.
• Realm 29 preview.

NODE 46

Endoscope

• Fibre carries illumination/images through paths.
• Medical imaging, industrial inspection.

NODE 47

Fibre Sensors

STRAINTEMPPRESSVIBE

• Optics + Sensing.
• Detects changes via light propagation properties.

NODE 48

Camera

• Lens + Aperture + Sensor.
• Object → Lens → Image → Sensor.

NODE 49

Eye vs Camera

CORNEA/LENSLENS SYS

PUPILAPERTURE

RETINASENSOR

• Biological vs Computational processes are analogous but not identical.

NODE 50

Binoculars

• Multiple elements for angular mag, upright viewing.
• Prisms fold light path. Extends telescope family.

NODE 51

Periscope

• Reflection (or TIR).
• Observation around obstacles, submarines.

NODE 52

Design Principle

LIGHT?MAGNIFICATION?RESOLUTION?

• Every instrument balances these three (plus distortion).
• Powerful design framework.

NODE 53

Mag vs Resolution

MAG = SIZERES = CLARITY

• Magnification: increases apparent angular size.
• Resolution: distinguishes two close details.
• High mag + poor res = large blur.

NODE 54

Diffraction Limit

• No instrument produces infinitely fine detail.
• Wave diffraction imposes limits. θ ≈ 1.22λ/D.
• Bridge to Realm 24.

NODE 55

Light Gathering

• Aperture is crucial. A ∝ D².
• Increasing aperture dramatically increases collection.

NODE 56

Experiment Lab

EYE MODELMICROSCOPETELESCOPETIR

• Lens focusing, magnifying glass, optical resolution.
• Camera obscura, acceptance angle.

NODE 57

Graph Chamber

• 1/f vs 1/u, P vs 1/f, m = v/u.
• NA vs index diff, Resolution θ ∝ λ/D.

NODE 58

Misconceptions

X

• "Eye emits light" → No.
• "Magnifier makes obj larger" → Increases angular size.
• "More mag = better scope" → Resolution matters.

NODE 59

Solving Engine

• Eye: Obj Dist → Accomm → Image → Retina/Defect.
• Inst: Obj → Obj Lens → Int Image → Eye Lens → Mag.
• Fibre: n_core > n_clad → TIR → NA.

NODE 60

Master Map

EYE → DEFECTSMICROSCOPE → TELESCOPEFIBRE OPTICS

• The entire realm compressed.

NODE 61

Deep Synthesis

BIOLOGICALINSTRUMENTALTECHNOLOGICAL

• Systems manipulate propagation to extract information.
• Limitation: Ray model cannot explain interference, diffraction, or polarization.