The Magnifying Glass

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The Magnifying Glass
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The angle that the objects subtends in (a) is
greater than in (b)
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A magnifying glass allows us to place the object
closer to our eye so that it subtends a greater
angle.
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The angular of magnification or magnifying power,
M, of the lens is defined as the ration of the
angle subtended by an object when using the lens,
to the angle subtended using the unaided eye with
the object at the near point of the eye.
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Telescopes
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Magnification of Telescope
M-fo/fe
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Reflecting Telescopes
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Aberrations of Lenses and Mirrors
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Distortion
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Chromatic Aberration
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Important Example

• An achromatic lens is made of two very thin
  lenses placed in contact, that have focal length
  of 25cm and 20 cm.
• Is this combination diverging or converging?
• What is the net focal length?

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Limits of Resolution
The ability of, lens to produce distinct images
of two point objects very close together is
called the resolution of lens.
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The two images are just resolvable when the
center of the diffraction disk of one is directly
over the first minimum in the diffraction pattern
of the other.