The image formation by convex lens is due to retraction. The rays bend and hence appear the come from a different point rather than an object, which is called an image.

In the image attached below, the refracted rays should only be visible to an observer to the right of the lens. enter image description here enter image description here But how are we able to watch the image even from the left of the lens, even though the refracted rays are not reaching an observer on the left.

Can someone explain why this happens?

  • $\begingroup$ Welcome to Physics Stack Exchange. I don't think that the image is visible to an observer observing from the left. The object is, but the image isn't. (I'm not sure) $\endgroup$ May 21, 2020 at 7:10
  • $\begingroup$ Even i thought that but I saw A video on YouTube of imave formation by convex lens and in it the image is clearly visible from behind the lens.Can someone explain why this happens. $\endgroup$
    – user265103
    May 21, 2020 at 7:13
  • $\begingroup$ Can you share the link? $\endgroup$ May 21, 2020 at 7:13
  • $\begingroup$ m.youtube.com/watch?v=FxQQ6fILi3k $\endgroup$
    – user265103
    May 21, 2020 at 7:15
  • $\begingroup$ Can you tell about the part of the video you're referring to? $\endgroup$ May 21, 2020 at 7:16

1 Answer 1


The image is upside down. That shows it is a real image, in other words the light actually converges to a point (as in the diagram you linked to). However the light rays do not stop at the image but keep on going. If you looked from far enough away to the right, without the mirror in the way you would be able to see the upside-down image. The mirror reflects the light back so that we can see it from the left side. It is like taking that diagram (with the lines extended) and folding it.

If you took the mirror away and put a white screen at the correct place you would see the image (upside down) show on the screen. You often need to experiment to find the place where the image is in focus; it might not be where the mirror is.

  • $\begingroup$ So after refraction the rays simply get reflected from the screen and thats why its visible?? $\endgroup$
    – user265103
    May 21, 2020 at 15:38
  • $\begingroup$ If it is a screen, it is placed at the (real) image. Light from each point in the object lights up just one point on the screen, making the image we see. The reflection is diffuse (light scatters in all directions) so the picture on the screen can be seen from anywhere, the same as with a projector. $\endgroup$
    – Peter
    May 21, 2020 at 23:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.