Question

how lenses are differentite

Answer 1

there are many types of lens.they are 1.convex lens 2.concave lens 3.plano convex 4.plano concave lens 5.concave convex lens
they differ in shap,propertys,
properties like convergens or divergens , image real or vertual , magnified or dimanished(of image)

Answer 2

because all the lenses are not same.there are many types of lenses concave,convex,plano concave,plano convex etc.