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Converging and Diverging Lenses
Lenses are used to focus light and form images.There are a variety of possible types We will consider only the symmetric ones
the double concave and the double convex.
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Converging at the Focal Point
For a double convex (i.e. converging) lens, the light refracts such that it converges at the focal point.
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Diverging from the Focal Point A double concave (i.e. diverging) lens has the
refracted rays diverging as if they all come from the focal point.
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Constructing Ray DiagramsDraw two of the three principal rays originating from
the same point on the object and follow these rules:
1. P-Ray is drawn through a point on the object and parallel to the principal axis.
It is refracted through the focal point, F.
2. F-Ray is drawn through a point on the object and through (convex) or towards (concave) the focal point.
it is refracted parallel to the principal axis.
3. V-Ray is drawn through a point on the object and through the vertex.
It goes straight through and does NOT change direction (assuming lens is thin)
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Rays – Converging Lens
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Image Types – Converging LensConverging = ConvexThe convex lens forms different image types
depending on where the object is located with respect to the focal point
5 possible object locations1. Case 1: The object is located in front of F2. Case 2: The object is located at 2F3. Case 3: The object is located beyond 2F4. Case 4: The object is located between F and 2F5. Case 5: The object is located at F, the focal point.
Please complete handout for CONVEX lenses (front half)(two examples are done for you on the next slides to help
get you started)
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Image Types – Converging Lens
Case #1: Object is Located in front of F
Notice that you refract the ray along the optic axis i.e. the middle of the lens
Image Properties – in front of F
L –
O –
S –
T -
Same side of lens as object
Upright
Larger
Virtual
Notice here that for location, you are telling me what SIDE of the lens the image is on (same side or
opposite side as the object)
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Ray Diagram - Converging Lens
Case #2: Object is Located at 2F
Image Properties – at 2F
L –
O –
S –
T -
At 2F – Opposite Side
Inverted
Equal
Real
Notice here that for location, you are giving an
approximate location (between __ and ___, or at
____), but you are also telling me what SIDE of the lens the image is on (same side or opposite side as the
object)
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Rays – Diverging Lens
Diverging = CONCAVE
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Ray Diagram - Diverging Lens
Locate the image of an object located between F and 2F for a diverging lens
Diverging Lenses
Complete the ray diagrams for concave/diverging lenses
You only need to complete two or three of these … if you catch on to the trend, you can stop!
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Complete the summary table for Image properties of Diverging and Converging (next slide)
Summary: Image Characteristics formed by Concave and Convex Lenses
Concave Lens (Diverging)
Object Location Size Attitude Location Type
Arbitrary
Convex Lenses (Converging)
Object Location Size Attitude Location Type
Beyond 2F
At 2F
Between F and 2F
At F
In front of F
