In this picture the concave lens forms an image that is smaller, erect and just in front of the actual object.
A concave lens is shaped like two half moons back to back, thin at the center and thick at the edges. Concave lenses are diverging lenses. Diverging lenses force light rays to bend away and never come together to a point. Concave lenses only produce virtual images which means the image is located on the same side of the lens as the light rays came from. These images produced are also erect and diminished.
A convex lens is shaped like two half circles, thin at the edge and thick at the middle. A convex lens is converging and can produce virtual and real images. A converging lens bends light inward so the light rays meet and form an image. This usually causes a real image wich is located on the opposite side of the lens that the light entered. The focal point of a convex lens and where you place the object in respect to the focal point is very important. There are two important places an object can be placed. Before focal point: image is virtual, erect and larger; magnifying glass. After the focal point: image is real and inverted. If the object is place very far from the lens the image gets small. For a magnifying glass the image's dimensions in respect to the object increase as the focal length increases. An image can be dim or bright. This is due to the light intensity over the image which increases with the diameter of the lens.
