CHROMATIC ABBERATION

Chromatic aberrations

Definition:

Chromatic aberration is defined as the defect produced in the system of a given lens in which the image of a white object is colored.
It is due to the reason that when light form white object refracts through the thick and large lens the angle of refraction varies with colour. 
Hence the focus of different colours if different. Therefore multiple coloured images are formed instead of a single white image.

Types of chromatic aberration:

There are two types of chromatic aberrations. 
They are 1. Longitudinal chromatic aberration and 
2. Lateral chromatic aberration.

1.Longitudinal chromatic aberration :


In this defect the white light from distant object is separated into seven colours after refracting through the lens and different colours converge at different focal points. 
The focal point of violet is nearer to the center of the lens as it refracts at less angle whereas the red colour is focused far away from the center of the lens.

The single focal point of lens without aberration

When the lens is thin:

The multiple focal points with longitudinal chromatic aberration When the lens is thick :

If a point white object is placed on the principle axis in front of the lens at a distance between f and 2f , the image of a white point object is not a single but colored point images from violet to red in the order formed on the principle the axis of the lens.

Magnitude of longitudinal chromatic aberration = fr – fv ,

since fr > fv

2.Lateral chromatic aberration

When an object of certain size is placed on the axis in front of a lens then violet coloured image is formed near to the centre of the lens and red image is formed at far distance on the principle axis. In between them other coloured images are seen.

The image of red colour is larger than that of violet and other colours.