Article about Contact lens Farsightedness Nearsightedness
Nearsightedness eyes can be normalized using eyeglass lenses and contact lenses. Eyeglass lenses are affixed to the eyeglass, while contact lenses are attached to the eyeball. Eyeglass has a certain distance from the eye, while contact lenses stick to the eye so that the distance between the contact lens and the eye can be ignored.
An example of problems experienced by a person with nearsightedness and farsightedness is explained, what types of lenses are used to normalize the eyes, what is the focal length and power of the lens. This focuses on the use of contact lenses in normalizing nearsightedness and farsightedness.
Farsightedness eye and contact lens
The farthest distance that can be seen clearly by a person with nearsightedness is 50 cm. For nearsightedness eyes to see infinite objects clearly, determine (a) the type of lens used, (b) the focal length of the lens and the type of lens, (c) the power of the lens.
Contact lenses are very close to the eyes, so ignore the distance between the lens and the eye. The distance between objects and image with the contact lenses is considered the same as the distance between objects and image with the eyes.
解決方案：
（A） 所用鏡頭的類型
Regarding nearsightedness, it has been explained that the lens used to normalize nearsighted eyes is a concave lens or diverging lens or negative lens.
（b）在 鏡頭的焦距
Objects that are observed in nearsighted eyes through contact lenses are at infinite distant, so the lens must form an image at a distance of 50 cm in front of the contact lens. The image is in front of the lens, so the image is virtual (compare the explanation regarding the image formation by the concave lens)
已知：
物距（do）= 無限
像距 (di) = -50 公分（負值表示像是虛像）
通緝： The focal length (f)
解決方案：
1/f = 1/do + 1/di
1/f = 1/~ + (- 1/50)
1/f = 0 – 1/50
1/f = – 1/50
f = – 50/1 cm = -50 cm = -0.5 meters.
The focal length is negative, means that the lens used is a 凹透鏡 還是 發散透鏡.
（C） The power of the lens
P = 1/f = 1/-0.5 m = -2 Diopters
The power of the lens is -2 D. Negative sign means that the lens used is a concave lens or divergent lens.
Nearsightedness eye and contact lens
The closest distance that can be seen clearly by a person with nearsightedness is 50 cm. For the person to be able to read at a distance of 25 cm like the average normal eye, determine (a) the type of lens used, (b) the focal length of the lens, (c) the power of the lens.
Contact lenses are very close to the eyes, so ignore the distance between the lens and the eye. The distance between objects and image with contact lenses is considered the same as the distance between object and image with the eyes.
解決方案
（A） 所用鏡頭的類型
用於矯正近視的鏡片是凸透鏡、會聚透鏡或正透鏡。
（b）在 鏡頭的焦距
For the observed object to be 25 cm in front of the eye, the lens must form an image at a distance of 50 cm in the front of the eye. The image is in front of the lens, so the image is upright and virtual.
已知：
物距 (do) = 25 厘米
像距 (di) = -50 公分（負值表示像是虛像）
通緝： The focal length of the contact lens
解決方案：
1/f = 1/do + 1/di
1/f = 1/25 + 1/-50
1/f = 2/50 – 1/50
1/f = 1/50
f = 50/1 = 50 公分 = 0.5 米
The focal length is positive means that the lens used is a convex lens or convergent lens or positive lens.
（C） 鏡頭功率
P = 1/f = 1/0.5 = +2 迪奧普TER值
The power of the lens is +2 D. Positive sign means that the lens used is a convex lens or convergent lens.
