Real and virtual images

The images formed by a lens can be:

upright or inverted (upside down compared to the object)
magnified or diminished (smaller than the object)
real or virtual

A is an image that can be projected onto a screen. A appears to come from behind the lens.

Convex lenses

The type of image formed by a lens depends on the lens used and the distance from the object to the lens.

A camera or human eye

Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the from the lens, the image is:

inverted (upside down)
diminished (smaller than the object)
real (can be produced on a screen)

Three light rays extend out from the object arrows and cross the lens at each end. These cross on the other side of the lens under a smaller green arrow. — Figure caption,
Ray diagram for an object placed more than two focal lengths away from a convex lens

Projectors

Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:

inverted (upside down)
magnified (larger than the object)
real (can be produced on a screen)

Three light rays extend out from the object arrows and cross the lens. These cross on the other side of the lens under a larger green arrow that is labelled 'image'. — Figure caption,
Ray diagram for an object placed between 2F and F from a convex lens

In a film or data projector, this image is formed on a screen. Film must be loaded into the projector upside down so the projected image is the right way up.

Magnifying glasses

A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. The image is:

upright (the right way up)
magnified (larger than the object)
virtual (cannot be produced on a screen)

Two light rays extend out from the object which is shown by a small green arrow that sits between F and the lens. The rays that extend to the image are in a lighter shade. — Figure caption,
Ray diagram for an object placed less than one focal length from a convex lens

Only the person using the magnifying glass can see the image. The image cannot be projected onto a screen because it is a virtual image.

Concave lenses

Concave lenses always produce images that are:

upright
diminished
virtual

Peep hole lenses

Peep holes are set into doors so the occupant can identify a visitor before opening the door.

Three light rays extend out from the object towards the lens. On the other side of the lens the rays bend in different directions. — Figure caption,
Ray diagram for an object viewed through a concave lens

For an object viewed through a concave lens, light rays from the top of the object will be and will on the other side of the lens. These rays will appear:

from the same side of the principal axis meaning the image will be upright
further from the principal axis, so the image will be larger than the object

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Lenses and ray diagrams - OCR GatewayReal and virtual images