Images in a concave lens
A concave lens always gives a small, upright image on the object's side.
Spectacles for short sight
Some spectacle lenses are concave lenses. Looking through them, a printed page looks a little smaller, but upright.
Can a concave lens ever form a bigger image than the object?
What this lesson covers
The idea
A concave lens always gives a virtual, erect and diminished image between F1 and the optical centre, whatever the object position; an object at infinity gives a point-sized image at F1.
Spectacles for short sight
Some spectacle lenses are concave lenses. Looking through them, a printed page looks a little smaller, but upright.
Can a concave lens ever form a bigger image than the object?
- No, its image is smaller than the object whatever the position
- Yes, when the object is close to it
- Yes, when the object is at F₁
Near and far
Slide the object far away and then close to the lens. Watch the image.
Always the same kind
At every distance the image was upright, smaller than the object and between F₁ and O, on the same side as the object.
A concave lens always gives a virtual, erect and diminished image between F₁ and the optical centre, whatever the position of the object. An object at infinity gives a point-sized image at F₁.
Notes
A concave lens always gives a virtual, erect, diminished image between F₁ and O, and a point-sized image at F₁ for an object at infinity.
Check yourself
A concave lens forms an image of an object. What is the image like?
Where is the image of an object at infinity, formed by a concave lens?
The image formed by a concave lens always lies
Can a concave lens give an enlarged image?
- Virtual, erect and diminished — correct. Yes!
- Real, inverted and diminished. A concave lens does not give a real image.
- Virtual, erect and enlarged. A concave lens always gives a diminished image. An enlarged virtual image comes from a convex lens, with the object between F₁ and O.
- At F₂, on the other side. A concave lens gives its image on the same side as the object, at F₁.
- At F₁, point-sized — correct. Yes!
- At the optical centre. The image is at F₁, not at the optical centre.
- beyond F₁, on the same side as the object. The image lies between F₁ and O, closer to the lens than F₁ is.
- on the other side of the lens. A concave lens gives a virtual image on the same side as the object.
- between F₁ and the optical centre — correct. Yes!
- No, its image is diminished for every position of the object — correct. Yes!
- Yes, when the object is very close to the lens. A concave lens gives a diminished image whatever the position of the object.
- Yes, when the object is at F₁. A concave lens gives a diminished image whatever the position of the object.