Magnifying Glass Principle

To see small objects or their details clearly, it is necessary to move the object closer to the eye, which can increase the viewing angle and form a larger real image on the retina. But when the object is too close to the eye, it cannot be seen clearly. In other words, to be observant, not only should the object have a sufficiently large angle to the eye, but also an appropriate distance should be taken. Obviously, for the eyes, these two requirements are mutually restrictive. If a convex lens is installed in front of the eyes, this problem can be solved. A convex lens is the simplest magnifying glass, a simple optical instrument that helps the eye observe small objects or details.
Taking a convex lens as an example, calculate its amplification power. Place the object PQ between the focal point of the lens L and the lens, and bring it closer to the focal point, so that the object forms an enlarged virtual image P'Q 'through the lens. If the focal length of the image of a convex lens is 10cm, then the magnifying power of a magnifying glass made of that lens is 2.5 times, written as 2.5 ×. If we only consider the amplification ability, the focal length should be shorter, and it seems that this can achieve any large amplification ability. However, due to the presence of aberrations, the commonly used amplification power is about 3 ×. If a double magnifying glass (such as an eyepiece) is used, it can reduce aberration and achieve a magnification power of 20 ×.
Focusing Magnifier
A magnifying glass installed on the focusing cover of a dual lens reflex camera. Accurate focusing is required for easy copying or microscopic photography. When used with single lens reflex cameras, it should be mounted on the eyepiece for use.