A magnifying glass (also referred to as a magnifier, magnifying lens, loupe, or hand lens) is a lens or combination of lenses used to magnify (or enlarge) an object. A magnifying glass enables people to magnify almost anything (e.g. books, newspapers, fine print, stamps, coins, antiques, art, jewelry, gemstones, foliage, insects, fingerprints, rocks, etc.). The magnifying glass was invented in 1250 by Roger Bacon. Today, over 750 years later, it is more popular than ever, assisting people with hobbies and crafts and also helping people with low vision, macular degeneration and other vision conditions to see better.
In this section, we will explain, in basic terms, some of the science behind how a magnifying glass works. But first a little history and background information:
Roger Bacon (1214 AD - 1294 AD), an English philosopher, scientist and Franciscan Friar, is credited with the invention of what we commonly refer to today as a magnifying glass. Some research on magnifying lenses, however, had been conducted at least 200 years earlier by Arab scientist, Abu Ali Hasan ibn al-Haytham (Alhazen), who is widely regarded as the father of modern optics. Bacon most likely built upon Alhazen’s work in his development of the magnifying glass.
Early magnifying glasses probably looked somewhat similar to what they look like today. They usually consisted of a glass lens and metal or wood frame. Magnifying glasses of old were mostly used by doctors and scientists.
Magnifying glasses became more versatile as technology improved and demand increased. Although most people probably think of the classic hand-held magnifying glass used by Sherlock Holmes, today there many different types of magnifiers available in a wide variety of shapes, sizes and magnifications. In addition to Hand-Held Magnifiers, there are also Hands-Free Magnifiers, Lighted Magnifiers, Page, Bar and Dome Magnifiers, Neck Magnifiers, Loupes, Linen Testers and Stand Magnifiers, and Pocket Magnifiers. Each of the magnifiers in these categories meets different magnification needs.
The terms “magnifying glass” and “magnifier” are more or less synonymous. An digital magnifier, for example, is a type of magnifier, but one would probably not refer to it as a magnifying glass. A magnifying glass is also sometimes referred to as a "hand lens". Loupes are also a type of magnifying glass. Loupes tend to be smaller and higher in magnification power than your typical handheld magnifier, and are often referred to as jeweler's loupes.
From its humble beginnings over 500 years ago, the magnifying glass has become an essential tool for countless applications. They can be very beneficial for individuals with low vision conditions and extremely helpful for anyone needing just a little extra help with the fine print. They are also indispensable for a wide array of industrial, scientific and educational applications. They are useful for numerous hobbies, including sewing, model building, genealogy, art, stamp collecting, coin collecting, antiquing and much more. We invite you to tell us what you use your magnifier for!
Now on to the science part...
In order to help you select the best type of magnifier to meet your individual magnification needs, we'll first discuss three main points -- lens size, magnification, and focal length -- which are key to how magnifiers work.
The lens size is the optical area of the lens, generally measured in diameter for round lenses or in length and width for rectangular or square lenses. The lens size is a very important component of a magnifier because the lens size needs to be large enough or small enough to use the magnifier effectively. (Some people want the largest lens size possible to see as much of a subject as possible. Other people want a small lens size to enable them to keep the magnifier in their pocket, purse or handbag.) In any case, purchase the magnifier to meet your particular needs.
The size of most round magnifying lenses is between 1 inch and 5 inches. The size of most rectangular or square lenses is also between 1 inch and 5 inches. It is very important to understand the relationship between the size of the magnifying lens and the magnification power of the magnifying lens.
As the size of the round, rectangular or square magnifying lens increases, the magnification power decreases. And, as the size of the round, rectangular or square magnifying lens decreases, the magnification power increases. (Example: A round magnifying lens that is 5 inches in diameter has a magnification power of approximately 2x; however, a round magnifying lens that is 1 inch in diameter has a magnification power of approximately 10x.) The magnification power is created by the curvature of the magnifying lens. You will notice that the smaller the diameter (or size) of the magnifying lens the greater the curvature of the magnifying lens, and the larger the diameter (or size) of the magnifying lens the smaller the curvature of the magnifying lenses. (Think of this curvature as the width of a round, rectangular or square lens.)
Magnifiers enlarge, or magnify, the size of an object to the naked eye. Magnification is the process of enlarging an object in visual size, normally through an optical lens. The degree to which an object is magnified is expressed as magnification or magnification power. A number followed by the letter “x” signifies the magnification power of a particular magnifier. It is the ratio between the apparent size and the true size of the viewed object behind the lens. 2x magnification power means that the magnifier will make objects appear two times as large as they actually are. 3x magnification means that the magnifier will make objects appear three times as large as they actually are, and so on. It is important to note that the magnification power of a particular magnifier is the magnification power when the magnifier is held at the appropriate distance from the object being viewed and the object being viewed is in focus. For example, if a 5x power magnifier is held too far away from the object being viewed, it will not achieve 5x magnification power. The optimal distance that a magnifier should be held from the object being viewed is referred to as the focal length. Focal length is described in greater detail in the section below.
Another term used as a measurement of optical power, but different from magnification is diopter. Diopter refers to the optical power (or strength) of the magnifying lens. It is the strength of the magnifying lens measured at one meter. Four diopters (4.0D) represent a 100% increase in magnification or 1x power magnification. A 20 diopter (20.0D) measurement is approximately equal to 5x power magnification. A rough formula to convert from magnification power to diopters is to multiply the magnification power by four.
Focal length is the distance from the magnifying lens to the object behind the lens when the object is in focus. To put it another way, the optimal distance between the object being magnified (when it is in clear focus) and the magnifying glass is the focal length.
As the magnification power increases, the focal length decreases; conversely, as the magnification power decreases, the focal length increases. The stronger the optical power of the magnifying lens, the shorter the required distance between the magnifier and the object behind the lens.
For example, if you are looking at a diamond through a 10x loupe, the distance between the diamond and the magnifying loupe will be very small (about an inch or so away). The focal length is therefore about an inch. Your eye will also need to be very close to the loupe.
If you are looking at fine print with a 2x hand-held magnifying glass, the magnifying glass will need be several inches away (roughly 6 to 8 inches) from the fine print to bring it into optimal focus. The focal length in this example is 6 to 8 inches.
If you are not using a magnifier at its correct focal length, the object you are viewing will appear out of focus, distorted, or upside down when trying to view it through the magnifying glass.
Relationship of Lens Size to Magnification
Please keep in mind, as the lens size (diameter) of the magnifier lens increases, the magnification power of the magnifier decreases. As the lens size of the magnifier lens decreases, the magnification power of the magnifier increases. This is a result of the amount of curvature in the magnifier (lens). Magnification power is a result of the amount of curvature in the magnifier lens. As the lens size increases, the amount of curvature in the lens decreases, resulting in lower magnification power of the lens. As the lens size decreases, the amount of curvature in the lens increases, resulting in higher magnification power of the lens. This is why higher magnification lenses are generally smaller in size than lower magnification lenses.
Field of View
The end result of magnification is to provide you with a magnified “field of view.” The field of view is the area of magnification you see through the lens. Generally, the larger the diameter (or lens area for rectangular or square lenses) of the lens the larger the field of view of the lens. However, not all magnifiers are the same and some have larger fields of view than others. Not all manufacturers identify the field of view as a specification of the magnifier.
Types of Lenses
Along with understanding the lens size, magnification and focal length, it is important to purchase the appropriate type of material or composition of the optical lens to meet your needs. A magnifying glass lens can be made of glass or acrylic (plastic) material. Each type of lens has advantages and disadvantages when compared to the other.
Generally, glass lenses allow more light to be transmitted through the lens and usually have very clear optical qualities. It is hard, but not impossible, to scratch a glass lens. A glass lens is generally heavier than an acrylic lens of the same size.
Acrylic lenses are used as an alternative to glass lenses. They are usually very lightweight compared to glass lenses. Acrylic is the common name for Poly(methyl methacrylate) (PMMA), a thermoplastic or transparent plastic, created in 1928. Its composition makes it less prone to breakage and shattering. With modern technology, it has become possible to produce magnifiers with exceptional optical qualities using an acrylic lens. A majority of today’s magnifier lenses come with a high quality acrylic lens. You can find a wide selection of high-quality acrylic lenses in all of the magnifier categories sold on the See It Bigger website.
One specific type of acrylic lens that is very well known is the Fresnel lens, created by the French physicist, Augustin-Jean Fresnel. The Fresnel lens is very thin, lightweight and permits a large amount of light to transmit through the lens. Fresnel lenses are normally used to make page, bookmark, or sheet magnifiers. To achieve different levels of magnification (2x to 4x), the Fresnel lens needs to be between two to five inches from the subject. (Please note the Fresnel lens is not as clear as other acrylic lenses or glass lenses.)
At See It Bigger, we sell a wide selection of brand name magnifiers, from leading optical industry manufacturers including Bausch and Lomb, Carson Optical, Eschenbach Optik, Konus, UltraOptix, and more. You can learn more about the different types of magnifiers that are available at the link below.