Accommodation is defined as the ability of an eye to focus the distant objects as well as the nearby objects on the retina by changing the focal length of its lens.
The far point of an eye is defined as the farthest point from the eye which can be seen clearly. The far point of human eye is at infinity.
The near point of an eye is defined as the nearest point from the eye up to which eye can see objects clearly. The nearest point of normal human eye is 25 cm from eye.
Defects of vision of eye:
Hypermetropia / long-sightedness is the defect of vision in which the eye cannot see the nearby objects clearly but can see the distant objects clearly.
Causes of Hypermetropia
Myopia is the defect of vision in which an eye cannot see the distant objects clearly but can see nearby objects clearly.
Causes of myopia
Short-sightedness cannot be corrected by the use of convex lens, why?
For an eye with short-sightedness, the light rays coming from distant objects should be diverged to retina which is possible only by using concave lens as concave lens is a diverging lens. Therefore, convex lens, being converging lens cannot be used to correct the defect of short-sightedness.
|The focal length of eye lens can be changed by the power of accommodation. The distance between the eye lens and the retina is fixed. Hence, the focusing is done by changing the focal length of the lens.||The focal length of the convex lens is used in a camera is of fixed type. Hence, adjusting the distance between the lens and the film does focusing.|
|Image is formed on the retina.||Image is formed on the film in camera.|
© 2019-20 Kullabs. All Rights Reserved.