When does the focal length of the eyes increase?


When the muscles are relaxed, the lens becomes thin. Thus, its focal length increases. The image is formed on the retina even on increasing the distance of an object from the eye. For this eye, the lens becomes thinner and its focal length increases as the object are moved away from the eye.

  • If the object in concern is at a distance, for the image to form at the retina, the focal length has to be large. Here, the ciliary muscles relax, thereby thinning the eye lens. The focal length increases and the image is formed perfectly on the retina.
  • In the case of near lying objects, the ciliary muscles contract and thereby thickening the lens. This causes a reduction in the focal length for ideal image formation.

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