order to understand lenses, one must first define some terms.
Focal point is the location at which rays parallel
to the optical axis of an ideal mirror or lens converges to a
focal length is the distance between the focal point
and the middle of the lens. It will be represented by F.
You will also see 2F being
mentioned. 2F just refers to two times the focal length.
distance from the center of the lens to the object will be referred
to as do.
distance from the center of the lens to the image will be referred
to as di.
Real Image is an optical image at which rays from
the object converge. It is inverted or flipped
Virtual Image is a point from which Light rays appear
to converge without actually doing so. It is upright
or in the same direction as the object.
concave lens is a lens thinner in center than edges
and is diverging.
convex lens is a lens thicker in the center than
at the edges and is converging.