- The size of the eye ball is too large or long.
- The focal length of eye lens is too short.
- The size of the eye ball is too small or short.
- The focal length of eye lens is too long.
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.|