Transcript:

In the eye, there is this lens, and that's the centre line of the lens. And what is happening in the lens is, it is getting light from the outside, which it is focusing on the retina. This is the retina, right? And this light is coming at an angle theta, let's say. Except there is more than one light ray coming here. There is lots of light. There is a light from here that is also focused. There's a light from here that is also focused.

So, the brain is getting this composite signal from the retina. This is the signal that is going to the brain. So it is integrating all of this signal over all angles of theta. And when you do that, you get this. This is the integrated signal over all angles, except in this complex exponent, you have sine of theta. This term is sine of theta.

Now notice, here it is, the t. Here it is, sine of theta, right? But for small angles, sine of theta is theta. So when you make this approximation of small angles, that is why the eye is only.