  A smartphone is a powerful learning aid in the hands of a large section of
students around the world. The camera of the phone can be used for several
learning purposes apart from its obvious purpose of photographing. If the focal
length of the lens of the camera can be determined, several experiments in
optics can be performed with it. In some recent works, the method of
determination of the focal length has been discussed. When a real image of an
object is formed by a lens of known focal length, one can determine either the
distance or the transverse magnification of the object if the other is known.
In this work we have shown that we can determine both the transverse size and
the distance of an object, by photographing it from two positions, separated by
a distance along the line of sight of the camera.
