# Why are two rays required for us to see an image?

Why not one? Well we can't even sigle out a 'one ray' exactly because it's still a thin beam but my question is why do we see the image in a plane mirror only at the point where they all meet? We could have also thought the rays come from some farther point, if we continue it behind the mirror past the point where image is formed... So why only at that point? Yes the light intensity will be more there but than why can't we see layers of blurred images. I am really confused. Also when we do the candle experiment for lenses we see blurred images on the screen till we reach the point where image is formed. So how can we even see those blurred images if image isn't formed there? If we can see them there why not in plane mirror?

You don't need two rays. You do need all the rays from one point on the image to come from one point on the object.

If the rays from many different parts of the object go to the same point, and you try to make an image there, the image colour will be a mixture of the colours from all those different object points. So it will be blurry.

Usually we don't want to form blurry images. An image is what it's called when it's not blurry. Although there is a field called non-imaging optics where you just want to get light from A to B and you don't care whether it makes an image or not. (Examples: getting sunlight onto a solar panel, or lighting up a wall)

What actually happens is that rays come out of the object, from all parts of the object, in all directions. In order to make an image, we want as many as possible to go to the same place. With simple lenses, we only need to check the "extreme" rays (e.g. ones going through opposite ends of the lens) go to the same place, and then we know that all the in-between ones also go there.

Regarding the plane mirror, it works because the brain is expecting to see an object that rays come out of in all directions. Yes, it's possible that an even further back object was sending out rays in specific directions to make it look like a front object was sending out rays in all directions. That's how (some types of) holograms work. Have you ever seen one? They can be trippy. And yes, a hologram looks like it's in front of the hologram screen (or behind it). It doesn't look like it's where the screen is. In fact, there's no way to tell whether something is a hologram or a real object, unless you walk over to it and touch it. Our brains assume the simplest explanation (that there's a real object) is the correct one.

• Thanks! I was pondering over it since too long. "You do need all the rays from one point on the image to come from one point on the object."- that was the key line and a brilliant logic. Would have upvoted but I still don't have 15 reputations:) Nov 3, 2020 at 14:14
• @Anonymous If you're satisfied with their answer, you can click the "accept" button and it will close this question and award points. Nov 3, 2020 at 14:18
• @N.Steinle I think askers are recommended not to accept answers so quickly, in case a better answer comes along. Nov 3, 2020 at 14:20
• @user253751 Indeed, but I've found that many times the questioner will be satisfied and forget to ever check again. Especially when the questioner is new to the site. Nov 3, 2020 at 14:22
• @DaddyKropotkin good prediction :P Sep 10, 2021 at 15:08