A lens forms an image of an object. There are two kinds of image:Real image: formed where light rays actually meet after passing through the lens. It can be projected onto a screen, and is always inverted for a single lens.
Virtual image: formed where rays only appear to come from. It cannot be projected onto a screen, and you see it by looking through the lens.The nature of the image from a convex lens depends on where the object is. Draw a ray diagram with two rays from the top of the object (one parallel to the axis then through F, one straight through the optical centre). The image is where they cross.
Object at 2F: image at 2F; real, inverted, same size.
Object between F and 2F: image beyond 2F; real, inverted, magnified. Used in projectors.
Object at F: rays emerge parallel, so no image forms (it is at infinity).
Object closer than F: rays diverge after the lens, so they only appear to come from a point on the object side. Image virtual, upright, magnified. This is a magnifying glass.A concave lens always gives a virtual, upright, diminished image.Example: a projector must give a large, real image on a distant screen, so the slide is placed between F and 2F, and it is put in upside down so the image appears the right way up.
Virtual image: formed where rays only appear to come from. It cannot be projected onto a screen, and you see it by looking through the lens.The nature of the image from a convex lens depends on where the object is. Draw a ray diagram with two rays from the top of the object (one parallel to the axis then through F, one straight through the optical centre). The image is where they cross.
Object at 2F: image at 2F; real, inverted, same size.
Object between F and 2F: image beyond 2F; real, inverted, magnified. Used in projectors.
Object at F: rays emerge parallel, so no image forms (it is at infinity).
Object closer than F: rays diverge after the lens, so they only appear to come from a point on the object side. Image virtual, upright, magnified. This is a magnifying glass.A concave lens always gives a virtual, upright, diminished image.Example: a projector must give a large, real image on a distant screen, so the slide is placed between F and 2F, and it is put in upside down so the image appears the right way up.