A magnifying glass is a convex lens, usually mounted in a frame with a handle, which is used to produce a magnified image of an object. The glass works by creating a magnified virtual image of an object behind the lens. However, the distance between the lens and the object must be shorter than the focal length for the glass to work. If the distance is not correct then the image will appear small and inverted.
Many magnifying glasses are mounted on a stand to insure the proper distance from the studied subject. They are also often used by the visually impaired.
The earliest evidence of any sort of magnifying device dates to 424 where a glass globe filled with water provided magnification to read small letters. In 13th century Italy the eyeglasses were developed.
The easiest way to focus and gain the highest magnifying power is to put the lens close to the eye and move eye and lens towards the object. It is easier to put the magnifier close to the object rather than the eye. This way the eye can be farther away and a image may be obtained easily; the focus is not very sensitive to the eye’s exact position.
A typical magnifying glass might have a focal length of 9.8 inches, corresponding to an optical power of 4 dioptres. Such a magnifier would be sold as a “2Ã—” magnifier. In actual use, an observer with “typical” eyes would obtain a magnifying power between 1 and 2, depending on where lens is held.