1 converging lenses if we think of a double convex lens as consisting of prisms, we can see how...
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Converging Lenses
If we think of a double convex lens as consisting of prisms, we can see how light going through it converges at a focal point (assuming the lens is properly shaped).
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Diverging Lenses
A double concave lens can also be modeled by prisms:
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Converging and Diverging Lenses
Terminology of ConvexLenses
Principal axis
Optic axis
Optical centre
Principal FocusSecondary Focus
Focal LengthFocal Length
In reality, light bends twice at the air / glass boundaries
On diagram, we show that light ray bends once: on the optic axis
Concave Lens Terminology
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Concave Lens is diverging.The Principal focus is virtual, in front of the lens.
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Principle Rays – Converging Lens
Lens has two focal points because light can go both ways and still focuses on one spot
Principle Rays – Converging Lens (Convex)
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Incident Ray Reflected RayParallel to principal Axis Through the focal point
Through the focal point Parallel to principal Axis
On the vertex of the lens Goes straight through and does NOT change direction
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Principle Rays – Diverging Lens
Concave lens also has secondary focus, behind the lens.On diagrams, light rays also bend on the optic axis.
Principle Rays – Diverging Lens (Concave)
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Incident Ray Reflected RayParallel to principal Axis Through the focal point
Aiming the secondary focal point
Parallel to principal Axis
On the vertex of the lens Goes straight through and does NOT change direction
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Ray Diagram - Converging Lens
Location of the image of an object located at 2F
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Ray diagrams– Converging Lens
Location the image of an object located in front of F
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Ray Diagram - Diverging Lens
Your turn: Locate the image of an object located between F and 2F for a diverging lens
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Image Types – Convering Lens
The convex lens forms different image types depending on where the object is located with respect to the focal point
S size can be enlarged or reduced A attitude can be inverted or
upright L image can be infront or behind
the lens T image can be real or virtual
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Image Types – Diverging Lens
The concave lens forms same type of image no matter where object is located:
S reduced A upright L in front of the lens T virtual
Concave Lens (Diverging)Object
LocationSIZE ATTITUD
ELOCATION TYPE
Arbitrary Smaller Upright Same side of lens as object
Virtual
Convex Lens (Converging)Object
LocationSIZE ATTITUD
ELOCATION TYPE
In front of F Larger Upright Same side of lens as object
Virtual
Between F and 2F
Larger Inverted Opposite side beyond 2F
Real
At 2F Equal Inverted Opposite side at 2F
Real
Beyond 2F Smaller Inverted Opposite side between F and 2F
Real
As object moves away from convex lens, real image moves closer to lens
When object is located at F, no image is formed (verify with ray diagram)
Summary: Image Characteristics formed by Concave and Convex Lenses
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The Thin-Lens Equation Sign Convention
Distances: positive for real negative for virtual
Heights : positive above axis negative below axis
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The Thin-Lens Equation
do = the distance from the mirror to the object
di = the distance from the mirror to the image
f = the focal length
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Focal Lengthf
Object Distancedo
Image Distancedi
+Converging Lens(Convex)
Object is in front of mirror
Image is REAL
(opposite side of object)
-Diverging Lens(Concave)
N/A. do is always positive
Image is VIRTUAL(same side as object)
Sign conventions: LENS Equation
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Magnification Equation for LENS
M
M
If |M| > 1, image is larger than object (enlarged)
If |M| < 1, image is smaller than object (reduced)
M > 0 for up-right images
M < 0 for inverted images
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