The center of a converging lens is generally thicker than its rim.
The center of a diverging lens is generally thinner than its rim.
There are exceptions regarding meniscus lenses
Examples for converging lenses:
All convex-plano lenses, all plano-convex-lenses, alle biconvex lenses …
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… as well as all meniscus lenses with identical radiuses :
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Examples for diverging lenses:
All concave-plano lenses, all plano-concave lenses, all biconcave lenses
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