Various lens shapes, and the location of the principal planes.ʟ̩ 
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Converging or positive lenses.
1 -  Symmetrical double convex lens. 2 - Asymmetrical double-convex lens3 - Plano- convex lens.  4 - Positive meniscus lens.
Diverging or negative lenses.
5 - Symmetrical biconcave lens.6 - Asymmetrical biconcave lens.7 - Plano-concave lens.8 - Negative meniscus lens.


ʟ̩Location of the principal planes depending on the geometry of the lens.File:LensEquals.png
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