Lenses
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Lenses
Lenses
Snell’s Law applies to light as it travels from the air into the lens and back into air.
Remember that light rays are always reversible – I see you – You see me.
The lensmaker’s formula also applies to lenses as it does for mirrors.
1/do + 1/di = 1/f
di/do = si/so
If the image is virtual di and si are negative.
•Rules for Lenses •In parallel – Out through the focal point •In through the focal point – Out parallel •In to the middle of the lens – Out thru the middle of the lens
•Light always goes toward the fatter part of the lens
Parallel Light through a Convex Lens
Convex Lens Convex lens Converging lens Fat in the middle lens Gathering light lens Magnifying lens
Images for Lenses Real images are always inverted and on
the other side of the lens from the object. They can be projected onto a screen and actually have light rays meeting at the image.
Virtual images are always erect and are
located on the same side of the lens as the object.
6 Cases for convex lenses
1 - Object at ∞
23456
Object beyond 2f Object at 2f Object between f and 2f Object at f Object closer than f
http://webphysics.ph.msstate.edu/javamirror/ipmj/java/clens /index.html
Case 6 for a Convex Lens
Convex Lens – case 6
Concave Lens concave lens diverging lens skinny in the middle lens spreads out the light lens wide angle lens all images are smaller lens and f is negative
Wide Angle Lens = Concave Lens
Concave Lens
The focal length for a plane lens is infinity!
Q - As the curvature of the lens increases, what happens to the focal point?
A lens made out of diamond!
Q - As the index of refraction for a lens increases, what happens to the focal point?
Blue light undergoes the greatest refraction – See reference tables.
Q– Which color will have the longest focal point in a convex lens?
Demo – overhead projector and smoke.
Focal Point for different colors
Chromatic Aberration
Different colors refract differently. They have different focal points. This is a problem when looking through other media like glass. This problem can be solved by coating the lens or by using a combination of lenses of different kinds of glass.
Spherical Aberration
When light rays pass through the edges of a lens, they do not form clear images. This problem may be solved by using only the center of the lens or by using a combination of lenses.
The EYE
1. Cornea 2. Iris 3. Pupil 4. Lens 5. Muscles 6. Retina 7. Blind Spot
Far Sighted
What lens would you use to move the image in?
Far Sighted
Near Sighted
What lens would you use to move the image out?
Near Sighted
Lenses
Snell’s Law applies to light as it travels from the air into the lens and back into air.
Remember that light rays are always reversible – I see you – You see me.
The lensmaker’s formula also applies to lenses as it does for mirrors.
1/do + 1/di = 1/f
di/do = si/so
If the image is virtual di and si are negative.
•Rules for Lenses •In parallel – Out through the focal point •In through the focal point – Out parallel •In to the middle of the lens – Out thru the middle of the lens
•Light always goes toward the fatter part of the lens
Parallel Light through a Convex Lens
Convex Lens Convex lens Converging lens Fat in the middle lens Gathering light lens Magnifying lens
Images for Lenses Real images are always inverted and on
the other side of the lens from the object. They can be projected onto a screen and actually have light rays meeting at the image.
Virtual images are always erect and are
located on the same side of the lens as the object.
6 Cases for convex lenses
1 - Object at ∞
23456
Object beyond 2f Object at 2f Object between f and 2f Object at f Object closer than f
http://webphysics.ph.msstate.edu/javamirror/ipmj/java/clens /index.html
Case 6 for a Convex Lens
Convex Lens – case 6
Concave Lens concave lens diverging lens skinny in the middle lens spreads out the light lens wide angle lens all images are smaller lens and f is negative
Wide Angle Lens = Concave Lens
Concave Lens
The focal length for a plane lens is infinity!
Q - As the curvature of the lens increases, what happens to the focal point?
A lens made out of diamond!
Q - As the index of refraction for a lens increases, what happens to the focal point?
Blue light undergoes the greatest refraction – See reference tables.
Q– Which color will have the longest focal point in a convex lens?
Demo – overhead projector and smoke.
Focal Point for different colors
Chromatic Aberration
Different colors refract differently. They have different focal points. This is a problem when looking through other media like glass. This problem can be solved by coating the lens or by using a combination of lenses of different kinds of glass.
Spherical Aberration
When light rays pass through the edges of a lens, they do not form clear images. This problem may be solved by using only the center of the lens or by using a combination of lenses.
The EYE
1. Cornea 2. Iris 3. Pupil 4. Lens 5. Muscles 6. Retina 7. Blind Spot
Far Sighted
What lens would you use to move the image in?
Far Sighted
Near Sighted
What lens would you use to move the image out?
Near Sighted
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