Why do our eyes need to be far from the lens to view a real image?

[SplinterCell]

I do understand that we don't need a screen to view a real image, but why our eyes need to be far away from the lens than the image? Why can't we be exactly where the image would normally appear if we had a screen? Moreover, the image there is sharp because the rays converge exactly at that point, so it supposed to be the perfect location for us.

 

[dauto]

You can't see the image if it is too close to your eyes for the same reason you can't see an object if it is too close to your eyes. Your eyes won't be able to focus the image on your retina. If you could remove your retinas from the back of your eyeballs and use them as a screen than your idea would work. You can't do that, can you?

 

[jtbell]

Why can't we be exactly where the image would normally appear if we had a screen?

To put dauto's response another way, we can't put our eye exactly at the image location and expect to see it, for the same reason why we can't put the object right on the front surface of our eye (let alone inside the eye :yuck:) and expect to see it (at least not very clearly).

Hold an object in front of your eye and slowly bring it in closer and closer. How close can you get it and still see clearly the fine details on it?

 

[272]

So if i stand behind the concave mirror and place a card where an image should be formed,
i will see the image on the card.color and everything?even though I am standing behind the mirror?please explain.

 

[davenn]

So if i stand behind the concave mirror and place a card where an image should be formed,
i will see the image on the card.color and everything?even though I am standing behind the mirror?please explain

no, how do you expect to see anything from behind a mirror ?
The image is reflected off the front of the mirror, nothing is transmitted through the mirror, else it wouldn't be a mirror would it ?Dave

 

[sophiecentaur]

So if i stand behind the concave mirror and place a card where an image should be formed,
i will see the image on the card.color and everything?even though I am standing behind the mirror?please explain.

You'd have to draw a picture of this. The verbal description doesn't really seem to make sense.

 

[272]

My confusion comes from my txt book. My txt. Book reads,"if you were to hold card at the position of the image,the image would show up on the card-the image is said to be focused on the card by the mirror." This is for an object outside the focal point of a concave mirror. So I am thinking of the mirror as a projector and the card as the screen. So that standing behind the mirror i'd see the image on the card. But i don't know. I don't have a concave mirror to check. So that's my question, would i be able to see the image on the card? Please explain. It would make sense to see a regular image because if for example i turned on a lightbulb i would see it on the card because of the light rays. So i should be able to see a regular image (not a light bulb)too right? assuming the room is properly lit.

 

[sophiecentaur]

So that standing behind the mirror i'd see the image on the card.

Yes. That's right but the rays from the mirror will go past the screen if you take it away. You need to stand in front of the mirror and a reasonable way beyond where the screen was and you will then see a real image. You can do this with a shiny spoon. No fancy equipment is needed. You will see the image and even put a pencil point to coincide with it. A (Concave) shaving mirror is even better for this because you can see 1. A virtual image with your head near it (well within the focal length) and 2. A real image of your face (enlarged and upside down) that appears in front of the mirror if you stand a long way off.