Question

Formula for focal length of concave lens used to rectify Myopiahi​

Answer 1

Answer:

Yes, we use a concave lens for a myopic eye whose focal length is equal to the far point of the eye. It can be proven mathematically and can also be reasoned out intuitively.

Firstly, I would like to represent the mathematical one. It goes as following:

Let's assume that the far point of a myopic eye has become F (instead of ∞ which is, as you know, the of far point of a normal adult human's eye).

Answer 2

Answer:

, we use a concave lens for a myopic eye whose focal length is equal to the far point of the eye. It can be proven mathematically and can also be reasoned out intuitively.

Firstly, I would like to represent the mathematical one. It goes as following:

Let's assume that the far point of a myopic eye has become F (instead of ∞ which is, as you know, the of far point of a normal adult human's eye).

Now, suppose that a person bearing such an eye wishes to see an object which is at an infinite using a lens. Of course, the lens will be a concave one (read the intuitive explanation for the reason behind using a concave lens for a myopic eye).

In such a case, u = -∞

and v= -F [obviously, the image distance should be F because the person can't see beyond F].

On applying the lens formula, we get