5. Spherical Lenses Flashcards

1
Q

Spherical lenses

A

part of a sphere

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2
Q

Convex lens

A

converge light
plus lens
for hypermetropiaco

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3
Q

Concave lens

A

diverge light
minus lens
for myopia

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4
Q

total vergence power for THIN lenses

A

sum of each surface

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5
Q
  • Principal / nodal point, N
A

point where the principal plan and axis intersect (light passing through here is undeviated)

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6
Q

First principal focus, F1

A

point of ORIGIN of rays which AFTER refraction are parallel to the principal plan

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7
Q
  • First focal length, f1
A

F1 to N

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8
Q
  • Second principal focus, F2
A

where incident light parallel to the principal axis BEFORE refraction and brought to after refraction

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9
Q
  • Second focal length, f2
A

N to F2
o Positive for convex
o Negative for concave
o Lenses are designated by the f2

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10
Q
A

B-first principal focus
F-second principal focus
C-first focal length
D-second focal length
A, E-nodal point

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11
Q
A

A, E-nodal point
C-first focal length
F-second focal length
B-first principal focus
D-second principal focus

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12
Q

thin lens formula

A
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13
Q

how to construct a ray diaram

A
  1. Ray from top of object passing through the principal point
  2. Ray parallel to the principal axis through / away from second principal focus
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14
Q

image formed by a thin convex lens outside F1

A

real, inverted, outside F2

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15
Q

image formed by a thin convex lens at F1

A

virtual, erect. at infinity

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16
Q

image formed by a thin convex lens inside F1

A

virtal, erect, magnified, further from the lens than the object

17
Q

imaged formed by a thin concave lens

A

virtual, erect, diminished, inside F2

18
Q

dioptric power

A

reciprocal of the second focal length in metres
* F = 1/f2
o F: vergence power in dioptres
o f2: second focal length in metres

19
Q

the shorter the focal length

A

the more powerful the lens

20
Q

converging lens with a second focal length of +5cm

A

F = 1 / 0.05 = +20D

21
Q

linear magnification

A

= I / O = v / u
o I: image size
o O: object size
o v: distance of the image from the principal plane
o u: distance of the object from the principal plane.an

22
Q

angular magnification

A

o Angle subtended by the eye governs the retinal image size
o Apparent size = size / distance

23
Q

the loupe

A
  • Bigger angle subtended by the eye = bigger image
  • Loupe is a convex lens
  • E.g. for the loupe = x8 loupe = 32D lens / 4
24
Q

magnifiying power

A

M = F / 4

F = lens power in dioptres

25
Q
  • Peripheral portion of the lens acts as
A

a prism
o Convex = towards axis
o Concave = away from axis

26
Q

prismatic effect

A

P = F X D
o P: prismatic power in prism dioptres
o F: lens power in dioptres
o D: decentration in cms

27
Q

increasing prismatic power

A

o Greater spherical aberration
o Ring scotoma
o Jack on the box effect