Image Formation

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Image Formation

• In order to form a coherent image, the eye, or
  some optical device, must focus or converge at
  least two light rays reflecting off of the same
  point on that object.
• The image seen is then the summation of all of
  the focused rays reflect off of all of the parts
  of the image.

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Virtual images vs. Real images

• Real Image Light rays from the same point
  intersect in real space on a ray diagram. Real
  images created by single converging lenses are
  inverted in most cases. The image formed by a
  human eye is a great example of this
• Virtual Image No actual intersection. Image
  formed behind lens/mirror.

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Eyeball
Mirror
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Converging Optics focus parallel light rays to
a single point

• Converging Mirrors
• Always concave in shape
• Real images form when ogtf
• Virtual images form when oltf
• Converging Lenses
• Always convex in shape
• Always form real images

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Converging lenses
Convex surface
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Diverging Optics separate parallel light rays
so that they NEVER intersect

• Diverging Mirrors
• Always convex in shape
• Images always virtual
• Diverging Lenses
• Always concave in shape
• Always form virtual images

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Diverging Lenses
Concave surface
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Lens Vocabulary
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Relationship between variables
Distance between object and optic
Focal length
Distance between image formed and optic
Magnification
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An important note

• The image distance for virtual images is ALWAYS
  negative in the lens equation.
• Be very careful with this. Dropping this
  negative can mess up your whole calculation.

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Drawing ray diagrams

• Draw a principal axis such that this line will
  pass through the center of the optical component,
  perpendicular to the optic.
• Draw the object as an erect (upright) arrow on
  the left side of the optic.
• --The height of the arrow will be proportional to
  the objects real size and its distance from the
  optical component proportional to the real
  distance, o.

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Finding images on a ray diagram(Converging
optics ONLY)

1. Incident ray parallel to principal axiscomes out
   through the focal point.
2. Incident ray into optics through focal
   pointcomes out parallel to the principal axis.
3. Draw image at point of intersection of rays.
4. Other rays can be drawn. (e.g., centerstraight
   reflection/refraction, etc..)

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Finding images on a ray diagram(Diverging optics
ONLY)

1. Incident ray parallel to principal axiscomes out
   through the focal point. Extend the point of
   interface behind the optic, through the focal
   point.
2. 2nd ray will be drawn to pass directly through
   the center of the lens/off the center of the
   mirror.
3. Draw image at point of intersection of rays.

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• Note that both types of optical components follow
  the same rules.
• We will study these in more detail in the coming
  days.

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Ray Diagrams A real image
f1 f2 o i