Waves‎ > ‎

Converging Lens

Convex lenses

A convex lens is also called a converging lens.

This type of lens can be used in cameras, projectors, some spectacles, and as magnifying glasses.
Ray diagrams can be used to represent what happens to light rays as they pass through the lens.
The magnification produced by a lens is calculated by comparing the image size with the object size.


A convex lens is thicker in the middle than it is at the edges. 
It is also called a converging lens because it converges light rays (brings them together). 

The principal axis is an imaginary line at 90° to the face of the lens, and passes through its optical center

Light rays passing through the lens parallel to the principal axis are focused to a single point. 

This is called the focal point. The distance from the center of the lens to the focal point is called the focal length.

When an object is placed in front of a lens, light rays coming from the object fall on the lens and get refracted. The refracted rays produce    an image at a point where they intersect or appear to intersect each other. The formation of images by lenses is usually shown by a ray diagram. To construct a ray diagram we need at least two rays whose path after refraction through the lens is known. Any two of the following rays are usually considered for constructing ray diagrams.


A ray of light passing through the Optical Center of the lens travels straight without suffering any deviation.

An incident ray parallel to the principal axis after refraction passes through the focus.


An incident ray passing through the focus of a lens emerge parallel to the principal axis after refraction.


Formation of a real image with a converging lens:

 Distance of object  Position of the image Properties of the image 

Further than 2F

 Between 2F and F

Real - Diminished - inverted 



Real - same size - inverted  

Between F and 2F

Further than 2 F 

Real - magnified - inverted  


 No image