magnifying glass

Simplest optical instrument, a hand-held converging lens used to produce a magnified, erect, and virtual image. ‘Virtual’ means that the light rays do not actually pass through the place where the image seems to lie. The image can only be seen by looking through the magnifying glass.

The object to be magnified must be placed between the principal focus and the lens; the image produced is best seen if it is at the near point of the eye. The magnification produced by the lens is given by the ratio:

magnification = height of image/height of object

This ratio can be shown to be equal to the distance ratio:

magnification = image distance/object distance

It follows that bringing the object closer to the eye increases the magnification.