Calculations with Optical Instruments
Magnifying Glass
A magnifying glass is a convex lens, meaning it curves outwards. Most magnifying glasses have a handle. They can be made of glass or another transparent material such as clear plastic. The more curved the lens, the shorter the focal length, and therefore the greater the magnification.
M = 25 cm / f
This is the formula for calculating the focal length and magnification of a magnifying glass. The conversion factor is the clear viewing distance, also called the standard viewing distance. This is 25 centimeters. This is a defined reference value from optics, which describes the average clear viewing distance of a healthy, young person. Such a young person can often still see an object clearly at a distance of 25 centimeters. If the distance decreases, this is usually no longer possible.
The focal length is the distance from the center of the magnifying glass to the object being viewed, such that it appears at its sharpest. The magnification indicates how many times larger an object appears when viewed through the magnifying glass. Reading magnifiers usually magnify 2 to 6 times. Detail magnifiers can achieve magnifications of 15 times and more. The higher the magnification, the closer the object must be to the magnifying glass. At 3 times magnification, the distance is slightly more than 8 centimeters, while at 12 times magnification it is only 2 centimeters.
The curvature of a magnifying glass doesn't have to be the same on both sides. Sometimes one side is flat and only the other is curved. In fact, there are many different shapes, with significant differences in image quality and manufacturing complexity. The magnification is the same on both sides, regardless of which way you hold the magnifying glass, but the sharper image with less distortion is obtained when the curved side faces the object being viewed.
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