Summary 6.2 Light and lenses
Refraction by lenses
Light moves in straight lines, but if light meets a piece of glass or another transparent material at
an angle, its direction changes. This is called refraction.
o For example when light is concentrated into one point using a magnifying glass.
In the picture, the middle of the lens is thicker than
the edges.
o This is a convex or positive lens.
Before the lens, the lines move in lines parallel to the
main axis of the lens.
After the lens, all the rays meet at one point: the focal
point.
In drawings, the focal point is indicated by F. The
distance from the lens to the focal point is called the
focal length.
o The shorter that length, the stronger the lens.
Creating images using a lens
You can use a positive lens to create an image of an object on a screen.
A lens in the camera produces a small image of the view in front of the lens on a light-sensitive
sensor chip. A computer in the camera records that image pixel by pixel in a file.
The lens makes sure that all the light from any one point on the object comes together at a
single point again: the image point I of the object point P. A single photo consists of millions of
such image points or ‘pixels’
If the image sensor is at the right distance from the lens, the photo will be sharp. A sharp photo
consists of pixels that do not overlap.
o If the sensor chip is not at the correct distance, the image will be blurred. The pixels
overlap and the picture will be blurred.
Object distance and image distance
To focus the camera, two distances have to be matched up:
1. the distance between lens and object, the object
distance o
2. the distance between the lens and the sharp image, the
image distance i.
Refraction by lenses
Light moves in straight lines, but if light meets a piece of glass or another transparent material at
an angle, its direction changes. This is called refraction.
o For example when light is concentrated into one point using a magnifying glass.
In the picture, the middle of the lens is thicker than
the edges.
o This is a convex or positive lens.
Before the lens, the lines move in lines parallel to the
main axis of the lens.
After the lens, all the rays meet at one point: the focal
point.
In drawings, the focal point is indicated by F. The
distance from the lens to the focal point is called the
focal length.
o The shorter that length, the stronger the lens.
Creating images using a lens
You can use a positive lens to create an image of an object on a screen.
A lens in the camera produces a small image of the view in front of the lens on a light-sensitive
sensor chip. A computer in the camera records that image pixel by pixel in a file.
The lens makes sure that all the light from any one point on the object comes together at a
single point again: the image point I of the object point P. A single photo consists of millions of
such image points or ‘pixels’
If the image sensor is at the right distance from the lens, the photo will be sharp. A sharp photo
consists of pixels that do not overlap.
o If the sensor chip is not at the correct distance, the image will be blurred. The pixels
overlap and the picture will be blurred.
Object distance and image distance
To focus the camera, two distances have to be matched up:
1. the distance between lens and object, the object
distance o
2. the distance between the lens and the sharp image, the
image distance i.
