# Concave Lens _ Image Formation

• -Castiel-
In summary, a concave lens will always form a real image for a virtual object, as long as the rays passing through the lens are diverging. This is due to the nature of a concave lens, which causes rays to diverge rather than converge. However, the exact position and characteristics of the resulting image will depend on the focal lengths of the lenses and their positions. Therefore, there is no general rule for whether a concave lens will always form a real image for a virtual object. It ultimately depends on the specific optics involved.

#### -Castiel-

A concave lens always forms a virtual image (for a real object), will it always form a real image for a virtual object? (that is, when rays converge on it)

If yes, why?

If no, why?

Ask yourself what happens to the rays leaving an object when they pass through a concave lens. Would they ever be brought together to form a real image?

sophiecentaur said:
Ask yourself what happens to the rays leaving an object when they pass through a concave lens.

They Diverge?

sophiecentaur said:
Would they ever be brought together to form a real image?

Yes?

If two rays are, as you say, 'diverging' then how can they meet at a point to form a real image? They are surely getting further and further apart. No?

btw, what is a "virtual object"? (I missed that when I first read it).

However . . . . if you have a convex lens, producing a real image and you put a concave lens between the first lens and the image it forms, then the resulting (real) image will be formed a bit further away than the original (real) image.

sophiecentaur said:
btw, what is a "virtual object"? (I missed that when I first read it).

sophiecentaur said:
if you have a convex lens, producing a real image and you put a concave lens between the first lens and the image it forms,.

This precisely. If you put a Concave Lens in front of an image (make the converging rays that form the said image, fall on the concave lens before they can intersect and form he image) then that image should act as an object (virtual?) for the concave lens.

So basically an actual object that you place in front of a lens, is a real object.

sophiecentaur said:
then the resulting (real) image will be formed a bit further away than the original (real) image

the original (real) image as you put it is no longer real because it was never formed, right? The rays were supposed to intersect but the lens intercepted them before that could happen. That is what I mean by a virtual object.

So again, for a virtual object, will a concave lens Always form real image?

That is if two converging rays were to fall on a concave lens could it diverge them so much that they appear to come from behind the mirror as opposed to only shifting a bit further.

You are talking of an intermediate image and not a virtual object here, I think.

In answer to your original question, I would say that you can produce a real or virtual image, depending on the focal lengths of the two lenses and the position.
A Galilean telescope has a convex lens with a concave eyepiece lens - producing a virtual image at a distance which you can actually focus you eye on. The optics inside some camera lenses produces a shifted real image because of the presence of a concave element. So there is no general rule.

-Castiel- said:
So again, for a virtual object, will a concave lens Always form real image?

Are you familiar with the thin-lens equation? If so, you can answer this question for yourself.

## 1. How does a concave lens form an image?

When light rays pass through a concave lens, they spread out and diverge. This causes the image to appear smaller and upright compared to the object. The image is formed behind the lens and can be projected on a screen or observed directly.

## 2. What is the difference between a real and virtual image formed by a concave lens?

A real image is formed when the light rays actually converge and intersect at a point, creating a sharp and focused image. This can be seen by projecting the image onto a screen. A virtual image, on the other hand, is formed by the apparent intersection of the diverging light rays. It appears to be behind the lens and cannot be projected onto a screen.

## 3. How does the distance between the object and concave lens affect the image formed?

The distance between the object and concave lens, also known as the object distance, affects the size and location of the image. A larger object distance will result in a smaller and more magnified image, while a shorter object distance will result in a larger and less magnified image.

## 4. What is the focal length of a concave lens and how does it impact image formation?

The focal length of a concave lens is the distance between the lens and the point where the light rays converge. It is a measure of the lens' ability to bend light. A shorter focal length results in a more divergent and wider spread of light rays, creating a larger and less magnified image. A longer focal length results in a smaller and more focused image.

## 5. Can a concave lens form a magnified image?

Yes, a concave lens can form a magnified image. However, the image will always be smaller than the object, as the light rays diverge and spread out rather than converging. The amount of magnification depends on the object distance, lens curvature, and focal length of the lens.