# Why do we need a screen to see a real image whereas a virtual image can be seen without a screen?

We did a physics practical in which I couldn't see the image formed by the convex lens without the screen. But I can see the virtual image formed by the plane mirror without a screen.

• Duplicate You do not need a screen to see a real image. Commented Dec 30, 2018 at 14:05

You can see real images without a screen. Just look through a converging lens. If what you see is upside-down, then you are seeing a real image.

You are only able to use a screen to show where a real image is because light rays physically converge to a point in space.

When you use a screen, the screen "sees" the real image just as if your eye was where the screen was$$^*$$. Then we see what is reflected from the screen.

For the plane mirror you are just seeing a reflection, just as if the "mirror image" of your world was placed behind where the mirror if located without the mirror actually being there. Seeing things in a mirror is essentially just like seeing things normally.

$$^*$$ This is neglecting the fact that your eye is also a lens, so in reality you don't want your eye to be exactly at the image.

• I had practical class in which I could not see the real image until I put a screen there Commented Dec 30, 2018 at 13:18
• @Monkyman If you had put your eye where the screen was you would have seen the real image. Screens are used to reflect that real image to your eyes. Commented Dec 30, 2018 at 13:20
• but then for a virtual image on a plane mirror you need not put your eyes anywhere but you can still comfortably see the image . why is that so ? thanks for helping out Commented Dec 30, 2018 at 13:22
• @Monkyman I have added more about the plane mirror Commented Dec 30, 2018 at 13:25
• @AaronStevens With practice or the help of a translucent screen you can see a real image in mid air. The difficulty in seeing the image is that you have to focus on a region without any material reference points. Have a look at the link that I posted in my comment above. Commented Dec 30, 2018 at 14:14

This might help. Try focussing the sun with a convex mirror on your hand. You can not merely see it. You can feel it. That is a real image. You cannot catch a virtual image on a screen. You can catch a real image on a screen. (Just as you could do it on your hand.) It is a more convenient way to see a real image. I my school physics lab, we would use pointed needles to determine the distances. We have to adjust the position of the image pin to avoid parallax. When the room was a bit dusty we could actually see the real inverted image of the object pin from the side.

• Your first experience is poorly described and could be dangerous depending on how it is understood. Please clarify, prove that it's safe or remove it. Commented Dec 30, 2018 at 19:07
• I fail to see what is so dangerous about using a convex lense to focus the sun into the skin. You would feel the heat and move the lense fast enough. Commented Dec 31, 2018 at 13:05

The mirror directs the reflected rays towards you so you see.

If you direct the rays from a lens towards you you will see the image.

So to see the image formed by an optical system the rays need to reach your eyes in some way.