You know this
Here is a useless bit of information, but one that I like.
A lentil is a biconvex seed from the plant, Lens culinaris, of the legume family.
When those crazy cats like Grimaldi were mucking about in the 1600s, they noticed that the bits of glass they were using were the shape of lentils....hence, the lens was born.
And, always remember; the distance between the object and lens (u), the distance between the image and lens (v) and the focal length of the lens (f) are related by the equation -