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Concave Lenses



basic diagram

ray diagrams




Types of Lens



types of concave 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



ray diagram for a concave lens




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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)



concave lens ray diagram #2




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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