Question

The far point of an eye is 185 cm. A corrective lens is to be used to allow this eye to focus clearly on objects a great distance away. What should be the focal length of this lens?

What is the power of the needed corrective lens in diopters?

Answer 1

a) consider an object at the required corrected near point - inf The required image distance is at 105 cm, since this is the nearest that the eye can focus clearly. With this information we can use this formula -

1/f = 1/v + 1/u where f is the focal length of the lens, v is the image distance, and u is the object distance. Because the image is a virtual one, v is given a negative sign.

1/f = - 1/105

f = 1.05m

b) The power in diopters is the reciprocal of the focal length in metres; this is 0.952 diopters