The Eye
The “Normal Eye”
- Far Point º distance that relaxed eye can focus onto retina
= ¥
- Near Point º closest distance that can be focused on to the retina
= 25 cm
Therefore the normal eye acts as a lens with a focal length which can vary from 2.5 cm (the eye diameter) to 2.3 cm which allows objects from 25 cm ® ¥ to be focused on the retina!
this is called “accommodation”
Diopter: 1/f Eye = 40 diopters, accommodates by about 10%, or 4 diopters