Lenses and Images

Different lenses produce different kinds of image
1. Converging Lens
  1. Convex - bulges outwards
    1. Causes parallel rays of light to converge (move together) at a focus
    2. Principal focus is where rays hitting the lens parallel to the axis meet
2. Diverging Lens
  1. Concave - caves inwards
    1. Causes parallel rays of light to diverge (spread out)
  2. Principal focus is the point where rays hitting the lens parallel to the axis appear to all come from
3. The distance from the centre of the lens to the principal focus is called the focal length
3 Rules for refraction in a converging lens
1. An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
2. An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
3. An incident ray passing through the centre of the lens carries on in the same direction
3 Rules for refraction in a diverging lens
1. An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus (so it appears to have come from the principal focus)
2. An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
3. An incident ray passing through the centre of the lens carries on in the same direction
Lenses can produce real and virtual images
1. A real image is where the light from an object comes together to form an image on a 'screen' - like the image formed on the eye's retina
2. A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place

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Lenses and Images

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