Concave Lenses



Concave lenses, unlike convex ones, bend light so that it moves away from the focal point of the lens.

When rays of light come into the lens that are parallel to the principal axis they bend away from the focal point in front of the lens as shown in the diagram to the right.		 foc p

The three rays of light that reflect off an object that we can use to predict the image placement using a concave lens are:

Ray 1: Light that travels into a concave lens parallel to the principle axis refracts out away from the front F.
Ray 2: Light that travels into a concave lens toward the back F refracts out parallel.
Ray 3: Light that travels into the center of a concave lens experiences no change in direction.



ray tr


Note that as was shown for convex mirrors, a concave lenses produces only one type of image - virtual images. These images will always be on the same side of the lens as the object and to view them you must look through the lens. These images can not be projected onto a screen, so these lenses can not be used in projectors or cameras to project an image.
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