How can we create an image at infinity using a converging lens?

[adjacent]

https://dl.dropboxusercontent.com/u/260388836/index.html

Let arrow height be 1cm.
focal length:1cm
So if I move the arrow to the focal point,image is not formed.(i.e formed at infinity)
But,
Lets move it to say 0.999
Now the image is virtual and is magnified to about 1000X
If I make it closer and closer to the focal point,the image will eventually be infinite in length
How is this possible?
Then what's the need for microscopes.

 

[mfb]

An image that is at an infinite distance is not really useful, as you cannot watch it.
An image at a very large, but finite distance is possible. That's exactly the way a simple microscope works.

A better microscope will use more lenses to correct for various technical difficulties (no lens is perfect, they react a bit different depending on the angle and color of incoming light and so on), but the basic idea is always the same.

 

[adjacent]

Ok. Now keep the settings as previously stated(but keep the object at the focal point) and imagine that you are putting your eye in at the focal length of the right side of the lens.
Will you see anything at the edge of the lens?
Even if the rays are coming parallel to your eye,you would still see some color.
But no rays are coming towards your eyes in that direction.

 

[adjacent]

An image that is at an infinite distance is not really useful, as you cannot watch it.
An image at a very large, but finite distance is possible. That's exactly the way a simple microscope works.

A better microscope will use more lenses to correct for various technical difficulties (no lens is perfect, they react a bit different depending on the angle and color of incoming light and so on), but the basic idea is always the same.

mfb,You didn't really explain this point.

If I make it closer and closer to the focal point,the image will eventually be infinite in length
How is this possible?

 

[Drakkith]

Ok. Now keep the settings as previously stated(but keep the object at the focal point) and imagine that you are putting your eye in at the focal length of the right side of the lens.
Will you see anything at the edge of the lens?

What do you mean "at the edge of the lens"?

Even if the rays are coming parallel to your eye,you would still see some color.
But no rays are coming towards your eyes in that direction.

With the arrow 1 cm away from a lens with a 1 cm focal length the light rays leaving the lens on the right side will be parallel to themselves. If you put your eye in the light path you will see an image of the arrow. However, the further away your eye is from the lens, the larger the distance between points on the image gets, and eventually not all of the light rays can enter your eye and you will not be able to see the entire arrow anymore.

If I make it closer and closer to the focal point,the image will eventually be infinite in length
How is this possible?

As you move the object closer to the focal point, the rays converge/diverge less and less until they are finally parallel, which is when the image will be infinite in length. Parallel light rays do not form an image of any type. Does that help? If not, what exactly is confusing about the situation?

 

[adjacent]

What do you mean "at the edge of the lens"?

I mean the "edge".The place furthest from the center of the lens.

As you move the object closer to the focal point, the rays converge/diverge less and less until they are finally parallel, which is when the image will be infinite in length. Parallel light rays do not form an image of any type. Does that help? If not, what exactly is confusing about the situation?

If I bring the image to 0.999999999999999 cm,the image height will be x.I don't want to move it to 1cm.Just close to it.So,as you move it closer and closer and closer,the image will be larger than the solar system.
How is this possible?

EDIT:The program will crash if you write that value.But think logically.

 

[Drakkith]

I mean the "edge".The place furthest from the center of the lens.

Yes, I know where the edge of the lens is. What I mean is that I don't know what you are asking when you ask, "Will you see anything at the edge of the lens".

If I bring the image to 0.999999999999999 cm,the image height will be x.I don't want to move it to 1cm.Just close to it.So,as you move it closer and closer and closer,the image will be larger than the solar system.
How is this possible?

What's the problem? That just means that the focal length of the rays is so long that by the time the light converges to a point the distance between the ends of the image is larger than the solar system. What exactly are you confused about?

 

[adjacent]

Yes, I know where the edge of the lens is. What I mean is that I don't know what you are asking when you ask, "Will you see anything at the edge of the lens".

Ok.Let's leave it.I first want the one below.

What's the problem? That just means that the focal length of the rays is so long that by the time the light converges to a point the distance between the ends of the image is larger than the solar system. What exactly are you confused about?

I didn't mention anything about increasing the focal length.Focal length is 1cm and the object is brought closer to it.So image length is increased tremendously.Why can't we build a microscope with this?We will bring the object really closer to the focal length by the means of a computer or something.
This is my confusion.
Look at the simulation link I provided.

 

[mfb]

Ok. Now keep the settings as previously stated(but keep the object at the focal point) and imagine that you are putting your eye in at the focal length of the right side of the lens.
Will you see anything at the edge of the lens?
Even if the rays are coming parallel to your eye,you would still see some color.

Why do you expect anything special at the edge?
You'll see light, but you will be unable to recognize objects as their image is totally distorted.

But no rays are coming towards your eyes in that direction.

Which direction, and why?

If I bring the image to 0.999999999999999 cm,the image height will be x.I don't want to move it to 1cm.Just close to it.So,as you move it closer and closer and closer,the image will be larger than the solar system.
How is this possible?

I don't see the problem. You'll need a screen the size of the solar system, and it won't work with visible light due to diffraction, but that is a different topic.

 

[Drakkith]

I didn't mention anything about increasing the focal length.Focal length is 1cm and the object is brought closer to it.So image length is increased tremendously.Why can't we build a microscope with this?We will bring the object really closer to the focal length by the means of a computer or something.
This is my confusion.
Look at the simulation link I provided.

The focal length of the lens is unchanged. The focal length of the light rays, by that I mean the distance the light travels before it is brought to focus, is enormous.

 

[adjacent]

The focal length of the lens is unchanged. The focal length of the light rays, by that I mean the distance the light travels before it is brought to focus, is enormous.

I think you all have misunderstood.
I am talking about virtual rays. 0.999999 cm is closer than focal length isn't it?

 

[Drakkith]

I think you all have misunderstood.
I am talking about virtual rays. 0.999999 cm is closer than focal length isn't it?

In the case of virtual rays it would be the "virtual" focal length of the rays. The diverging cone of light looks like it is coming from a point X cm's in front of the lens, where X is the image displacement in your program. At 0.9999999 cm, the image displacement is very, very far away.

 

[adjacent]

And Image gets large and will look very large?(Like magnified 10000X)?

 

[jtbell]

The image is indeed very large, but how far away is it?

When you look at an object or image, its apparent size depends both on its actual size and on its distance from you. Try calculating the angular size θ of the image, where

tan θ = (height of image) / (distance of image from your eye)

Try it for different object locations, e.g. 0.9 cm, 0.99 cm, 0.999 cm.

 

[Drakkith]

And Image gets large and will look very large?(Like magnified 10000X)?

Yes, but beyond a certain magnification the image just becomes a blurry mess. I just tried it using a telescope eyepiece, and the virtual image had a limit to how big it could get before I could no longer see any detail.

 

[adjacent]

The image is indeed very large, but how far away is it?

When you look at an object or image, its apparent size depends both on its actual size and on its distance from you. Try calculating the angular size θ of the image, where

tan θ = (height of image) / (distance of image from your eye)

Try it for different object locations, e.g. 0.9 cm, 0.99 cm, 0.999 cm.

I pu my eye in the focal point
Yes in that way,if the focal length is unchanged,the angular size is always the same.If your eye is in the same place.So the image should always look the same size.But this is not the case.Am I getting something wrong?

 

[Varun Bhardwaj]

It depend on the quality and size of lens that how much you can magnify image on the edge of lens
If you want to magnify a image infinite than you require infinite quality and size of lens,that is not possible
It is thing to think but not to do really.

 

[adjacent]

It depend on the quality and size of lens that how much you can magnify image on the edge of lens
If you want to magnify a image infinite than you require infinite quality and size of lens,that is not possible
It is thing to think but not to do really.

Am I dong it?Or going to do it?
I am just thinking.Ya know..

 

[adjacent]

The image is indeed very large, but how far away is it?

When you look at an object or image, its apparent size depends both on its actual size and on its distance from you. Try calculating the angular size θ of the image, where

tan θ = (height of image) / (distance of image from your eye)

Try it for different object locations, e.g. 0.9 cm, 0.99 cm, 0.999 cm.

I put my eye in the focal point
Yes in that way,if the focal length is unchanged,the angular size is always the same.If your eye is in the same place.So the image should always look the same size.But this is not the case.Am I getting something wrong?

Please elaborate,jtbell.

 

[adjacent]

jtbelllllllllllll

 

[mgdaubo]

Hi all,
I have another question related to this.

Suppose we move the arrow to 0.9999 cm as adjacent said, then the virtual image will be very far, will it give us the feeling like we are seeing an object at infinity?
In my case I want to make something like a Head-up-display which create image at infinity. I imagine I will put a lens in front of a screen and adjust the distance to get virtual image at infinity. I tried with a converge lens: use 10cm focal lens, and move the screen close to focal plane, I expected to see the screen as it is about some meters away from me, but it was not. What is not correct in my understanding? I just want to bring a screen says at 10cm distance from my eye to a further distance says 2m, how can I do that?