How To Choose  Lens 

A lens is a piece of transparent material that refracts light in regular
way.It is bounded by one or two spherical surfaces.There are two main types of
spherical lens.

1. Convex lens
2. Concave lens

Convex Lens

  A lens which is thick at the center and thin at the edges is called
a convex lens.It converges parallel beam of light at a point and hence is also
called a converging lens.
There are three types of convex lens :

Double Convex Lens :-

Both The Surfaces of this lens are convex.

Plano-Convex Lens :-
One of the two surfaces of this lens is plane and other is
convex.

Concave-Convex Lens :-

One of the two surfaces of this lens is concave and
other is convex.

Concave Lens

  A lens which is thinner at the center and thicker at the edges is
called a concave lens.It diverges a parallel beam of light, hence it is also
called A Diverging lens.

There Are Three Types Of Concave Lens :

Double Concave lens

Both the surfaces of this lens are concave.

Plano-Concave lens

One of the two surface of this lens is plane and other is
concave.

Convex concave lens

On of the two surfaces of this lens is convex and
the other is concave.

Now You Are Able To Select lens !

Now People Ask Me What Is Aperture Okay
Actually Aperture Is the Diameter of lens is called aperture of lens.

Optical Center :

  The Geometric Center Of A Lens Is Called The Optical Center.

Power Of A Lens :-

The Reciprocal of focal length of a lens is called power of a
lens.The positive and that of concave lens is supposed to be negative.