Spherical Aberration

Our Earth is an extremely colourful place to live

And often we are tempted to capture pictures so that we can preserve the image forever

But there can be multiple instances when the camera lens fails to capture the image perfectly

The colours of the image image might turn out to be blurry as shown above

Sometimes the image might also look distorted

All these abnormalities are due to the phenomenon called Aberration

Aberration mainly can be of two types- Spherical or Chromatic Aberration

Spherical Aberration is the inability of a lens to form a point image of an axial point

While Chromatic Aberration is due to the fact that different colours have different focal points

Let us study Spherical Aberration

Spherical Aberration arises due to the spherical nature of the lens or mirror

It can be defined as the inability of the lens to form point image of an axial point

Let us now focus on the reason behind why such kind of Aberration occurs

The rays of light coming farther from the principal axis are called Marginal Rays

The Marginal Rays are refracted more, and thus meet at a point close to the optical centre()

While the rays closer to the principal axis are called para axial rays

These para axial rays are refracted less, hence meet at a point farther from the optical centre ()

Thus, two images are formed at and , and hence the final image formed is not clear

Now it is important to note, that Aberration, be it of any kind, cannot be eliminated completely but can only be minimized

Let's see some methods to minimize Spherical Aberration

The first method is by using stops

By using stops, we allow only the Marginal Rays or the Para axial Rays to pass to form the final image

The images will be formed either at due to marginal rays or at due to paraxial rays

Eliminating a second image by using stops, we obtain a clear and final image by reducing spherical aberration

The second method to reduce Spherical Aberration involves the usage of Parabolic Mirrors

We know in case of mirrors also, the Marginal Rays would be more reflected than the Paraxial Rays

Due to this various focal points are obtained and hence the image gets distorted

The distance travelled by the marginal rays are more than the distance travelled by the paraxial rays

Hence, by using a Parabolic Mirror, we ensure that the distance travelled by all the rays are equal

In this method, by using the Parabolic Mirror we create one focal point for all the rays, resulting in the formation of one image

The last method of reducing the Spherical Aberration is by using a lens or mirror with large focal length

Now we know, Thus, if focal length is very large, then Spherical Aberration will be very small

Revision

Spherical Aberration is the inability of a lens to form a point image of an axial point

Spherical Aberration can be minimized by three methods: (a) By using stops (b) By using a Parabolic Mirror (c) By using a lens of large focal length

The End