4.1 - Magnification Flashcards

1
Q

Why consider image size?

A
  • Leads to important results about blur = understand refractive error
  • Gives an insight into the magnification produced by different refractive corrections (spectacles, contact lenses, refractive surgery) – don’t all produce same level of magnification
  • Has direct clinical relevance to aniseikonia
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2
Q

What is transverse magnification

A
  • Ratio of image height to object height ( h )

- Gives a relative size of how big image ( h’ ) is compared to object

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3
Q

What is equation for transverse magnification - for finite object

A
M = L/L' 
M = h'/h
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4
Q

What can the equation for transverse magnification be applied to

A

Any single surface or thin lens ( one surface where refraction takes place )

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5
Q

Why is transverse magnification called transverse

A

As its measuring image and object heights across the optical axis i.e. vertical heights

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6
Q

What values do we need to find out mag and image height

A

L and L’

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7
Q

How to work out retinal image height

A
  1. Object location l: L = n/l SO l = n/L
  2. Refraction at eye ( image vergence ): L’ = L + Fe
  3. Magnification: M = L/L’
  4. Retinal image height: h’ = M X h
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8
Q

What is the power of the eye

A

+60D

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9
Q

Is eye low or high power

A

High

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10
Q

What is magnification for real objects forming real images on or near the retina

A
  • Negative therefore image on back of eye from real object is inverted
  • Less than 1 cause power is high and positive = retinal image is much smaller than the object looking at
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11
Q

What does image on retina have to be for it to produce a response

A

Real

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12
Q

What happens in multiple surface/thin lenses

A

Image formed by one surface acts as object for the next ….
-If we can work out what the 1st lens does in terms of image it produces we take that info/image and use it as the object for the next surface and keep going through the surfaces all the way through the system

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13
Q

What happens when sp lens in front of reduced eye

A

Have 2 surfaces to take into account

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14
Q

How do you work out magnification for finite object for multiple surfaces i.e sp lens before eye

A
  1. Object location l1: L = n/l SO l1 = n/L
  2. Refraction at lens ( image vergence ): L’1 = L1 + Fsp
  3. Step along i.e. vergence at eye: L2 = L1’/(1 − dL1’)
  4. Refraction at the eye: L2’ = L2 + Fe
  5. Magnification: M = L1/L1’ X L2/L2’
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15
Q

What is finite object transverse magnification equation for multiple surfaces

A

M = L1/L1’ X L2/L2’

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