The optical aids are based on the principle of reflection, refraction and diffraction of optics. Secondary vision equipment with concave and convex mirrors or lens enlargement images can be provided depending on the needs of seeing or seeing. Such auxiliary equipment can be divided into three categories.
The first category is handheld magnifiers and telescopes: use the hand to adjust the focus to read. Ordinary hand-held magnifier is not high magnification, in principle, should have more than three times the amplification function with lighting equipment is better; hand-held telescope with single glasses and double glasses of the points, due to the general amblyopia students in two eyes great difference in vision It is more suitable to use single glasses type.
The second type is a desktop magnifier: When used, the reader is first fixed on the table, then the magnifier is placed on the reading material, and the magnifier is read by hand. Some of these types of magnifiers have fixed focal lengths, some of which can be adjusted in focal length. The shape of the lens is round, square, or long. 😃
The lens is surrounded by a bracket or a vertical cylindrical stand. In principle, it is better to use a rectangular shape, a strip shape, a large lens area, a lighting device, and a magnification of three times or more. Such magnifiers, such as with a desk with a slope, can maintain an upright posture when reading, and a larger lens area can reduce the number of lens movements and reduce eye fatigue.
Magnifier made round because most of the factors in the production process is relatively simple, but also easier to use, but there are also square magnifiers, but as long as you can magnify the magnifiers are good.
Magnifier made round to good reading.☀
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