The magnifying glass, a convex lens used to magnify objects, was first invented by Alhazen in 1021. It inspired the microscope and revolutionized biology and chemistry. The magnification is determined by the lens’ optical power and distance from the object. The area covered by the lens is the area being shown, and each point viewed has its own ideal focal distance. The light is bent to meet at a point, which can cause objects to appear upside down at close range.
A magnifying glass is simply a convex lens meant to be brought close to an object to see it magnified. It is a very simple form of microscope and its invention allowed many subsequent breakthroughs in optics to occur. The magnifying glass is particularly visible in mystery fiction and is iconically associated with the fictional character Sherlock Holmes, who used one to study a crime scene in order to locate clues.
The first recorded magnifying glass was created by master scientist Alhazen in 1021. He published a comprehensive work, The Book of Optics, which expounded many principles of optics and many interesting devices. One of these has been described as “a magnifying device, a convex lens which forms a magnified image”. This basic invention went on to inspire many others, including the microscope, which helped revolutionize the fields of biology and chemistry.
The magnification of a glass is determined by the optical power of the lens and by the distance it is kept from the observed object and from the eye. A typical one would be labeled a 2X magnifier, implying that the size of objects being viewed is doubled, although that’s likely to be better than most average users would get. On the other hand, someone with relatively poor eyesight could use such a tool to achieve even greater relative magnification.
Although some people think that a magnifying glass cuts off the area being viewed, in reality the area covered by the lens is the area being shown. Unlike straight vision, however, some areas are much larger than they would be with the naked eye, while others are much smaller. Each point viewed under the lens has its own ideal focal distance, which is why most people move the glass closer and closer to the object being viewed to find the ideal distance.
The best way to think about how a magnifying glass works is to first imagine it in a two-dimensional situation. If a person imagines something under glass, such as a ladybug, he can imagine two lines rising into the air from either side of the insect. Under a regular piece of glass, those lines would travel straight and never meet, and the viewer would see both points of the ladybug relative to where they actually are. With a magnifying glass, however, the light is bent in such a way that the two invisible lines eventually meet in the air. An ideal distance has that point right in the eye.
After these two imaginary lines meet, they cross and cross in the opposite direction. This is why at extremely close range, an object under the lens may appear to be upside down. The light has continued to move, but has reversed its orientation as it is seen.
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