Home >> Optics, concave lenses

Types of lens

All four types of concave lens are diverging lenses. That is, they diverge parallel rays of light from a focus, producing a virtual image.

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Basic ray diagram

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Ray diagrams

Ray diagrams are constructed by taking the path of three distinct rays from a point on the object:

note - the lens is considered to be so thin as to be represented by the axis of the lens(green)

A) a ray passing through the optical centre of the lens

B) a ray parallel to the principal axis, which refracts through the lens and appears to have come from the principal focus

C) a ray heading towards the principal focus(on the opposite side of the lens) and being refracted through the lens, emerging parallel to the principal axis

For all the object positions listed below,

object between f and the lens
object at f
object between f and 2f
object at 2f
object at infinity

the ray diagrams are virtually the same as in the diagram above. Hence the result is the same. The image produced is virtual, upright, diminished and on the same side of the lens as the object.

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