# Where is the "infinity" where image of an object kept at focus of a convex lens being formed?

Here the object is AB kept at first focal point F₁, and we see the light rays emerging parallel to each other, meeting at infinity.

When the object is kept at focus of a convex lens we say that image is formed at infinity. According to classical optics if image is to be formed then at least two rays must intersect. But in this situation we don't see any two rays intersecting. Nevertheless we can see the image.

So this might mean that that parallel rays are intersecting at infinity but where exactly?

• where do you think they intersect, if anywhere? Oct 10, 2021 at 11:28
• You don't see the image unless you add another lens. This may be the eye lens.
– nasu
Oct 10, 2021 at 11:45
• You can't see an image in that case. The lens will just be filled by a more or less uniform mush of colour. Oct 10, 2021 at 11:45
• They don't Meet at INFINITY. They meet at any finite distance when we see image. Oct 13, 2021 at 6:57
• One way to look at "focus at infinity" is to think of a lens with the object at the focus as a system that converts spatial position to angle. Consider the tip of the arrow in your diagram. As I change the length of the arrow, rays starting at the tip (regardless of what direction they leave the tip) always form parallel rays after the lens, but the angle of the parallel rays changes. Oct 13, 2021 at 10:59