Why rays of light from different points don't form an image?

Question

I'm asking a clarification about this questions: Why does an image only form where light rays coming from a single point get reflected or refracted and converge to a common point?
I want to know if the answer to that question given by Farcher is correct (The question has to be interpreted as it was by Farcher, not by the other answerer).

Namely the question is, why only the rays coming from a single point of an object form an image when focused by a lens, for example on the retina? Because as shown in that questions rays of light geometrically can be thought as originating from all points of space not only from the ones in which is located the surface of an object.
So what's the physical mechanism that permits the retina or the lens to distinguish the points from which the light is really originating and the points in which the light rays are only crossing?

Answer 1

The way I understand your question is that you are asking that why is the eye able to distinguish between the image formed by rays emerging from the same point source and the image formed by rays emerging from different point sources.

The answer is that the eye does not know which rays are from the same point source and which are from different point sources, but instead the eye lens continuously changes its focal length to form the image which is most logical to the brain. A similar process is done by you when you change the focus of camera to put different objects in focus:

You will see that in the second picture the camera forms a clear image of twigs by accurately forming the image of each point on the twigs, but does not form a clear image of the flower as rays emerging from different point sources are being converged. Similarly the eye forms different images of the same scene by adjusting the focal length of the lens, which are then checked by the brain and you see the final image that brain perceives to be the most logical after this process.

You can try this by looking at a very distant object(a tree) which is behind a very close object(a pen). You will notice that once you focus on the tree, then pen becomes blurry, and when you focus on the pen, the tree becomes blurry.

Answer 2

The real way to say it is that we SEE an image at such a point. Why is this so? This is how we have learned to see. Light from a small button spreads out, refracts through the lens of our eyes, and then comes together on a small portion of the retina. This is what we call seeing the button. When the button is too close, the light from the button spreads out over a large portion of the retina. We call this blurred. This looks the same as a button at a focused distance spread out over a large area, kind of like what a smeared out dot of paint would look like. All of this is seeing an object without any extra mirrors or lenses.

When we look at an image, the brain interprets it to be the real thing it looks like on the retina. For the image of a small dot to look like a small dot, light has to "look like" it is spreading out from a small dot when that light reaches our eyes. Light that would come together behind your head, if your head were not in the way, is light coming together rather than spreading out. It won't make a pattern on the retina that looks like anything real. A real image is light that spreads out from where light rays come together.

A virtual image is when light is spreading out, but not really from a location on your side of the mirror or lens. The light rays of a virtual image are lined up as if they are spreading out from the other side of the mirror or lens. It still looks like something real to your brain, but it looks like it is on the far side. This is why your image in a bathroom mirror looks like it is behind the mirror. Light from your nose reflects and comes together on your retina to make the pattern of a nose on your retina. Light from your eye comes together on your retinal to make the pattern of an eye. All these pieces make all the parts of your face at different locations on your retina, thus making up your whole face.