Information on Magnification Glasses

Almost everyone has used a magnification glass at some point, whether it's to examine an object in science class or to make it easier to read the fine print of a document. And almost everyone has them lying around, these powerful devices that can make research and reading not just easier. For some, a magnifying glass makes it possible.

The Lens

The most important part of a magnification glass is the lens. The lens is the piece of glass that enlarges the image, by using a combination of light and refraction. While there are different types of lenses, the type used for magnification is a convex lens (meaning that the surface of the glass curves outward rather than inward).

The curve of the lens must have complete axial symmetry to be effective---meaning that the curve of the lens is the same around the circle. When the light strikes the lens, it is refracted through the glass and makes anything viewed through the lens seem larger.

The First Magnifying Glass

The first magnifying glass was developed in approximately 1021 by Alhazen, an Arab/Persian scientist and mathematician. Alhazen was fascinated by the wonders of the human eye and how we perceive the world around us. He's often been credited with being the father of optical science and was also one of the first to experiment with optical illusions.
He was the first to examine and calculate the magnifying principles of the lens, documented what is perhaps one of his most famous works, The Book of Optics. It was in this book that the details and constants of magnification, mirrors and refraction were first outlined.

The magnifying glass became popular in Europe in the 12th and 13th centuries---after Alhazen's book was translated into Latin.

Focal Distance

Since the lens of the magnification glass is curved, the distance that the light must travel from the object, through the lens and into the eye of the person viewing it is different. This is why, when viewing an object through a magnification glass, the center of the object might be in sharp focus and become blurry near the edges. This is also why the viewer may find that moving the glass closer to or farther from the object will bring objects into sharper focus.

Different people viewing the same object need to hold the glass at different distances to get the same effect. Each human eye is unique, and each individual must find the proper distances to get the desired effect, much like adjusting the field of a microscope.

Considerations

The amount that an object is magnified is also relative to an individual. While a glass might be rated at 2x (indicating that it will magnify the object two times), a person with poor eyesight might gain a more noticeable benefit from it.

A magnifying glass typically works by bringing it closer to the eye in order to find what is called the near point---the point at which the image looks the clearest. In older individuals, the near point can be up to several meters away, making it seem as though the image is magnified much more than it would be to a younger person with a closer near point.

Limits

While magnification increases the size of the object and the detail that is visible, there is a limit to how much something can be magnified. The detail of an object can only be increased until it reaches the limit that the human eye can discern. Most hand-held magnifying glasses magnify an image about two times, or doubling the size and the amount of detail that can be seen.