Diopter Change in Diving Cormorants Double-crested cormorants (Phalacrocorax aur

Question

Diopter Change in Diving Cormorants Double-crested cormorants (Phalacrocorax auritus) are extraordinary birds - they can focus on objects in the air, just like we can, but they can also focus underwater as they pursue their prey. To do so, they have one of the largest accommodation ranges in nature - that is, they can change the focal length of their eyes by amounts that are greater than is possible in other animals. When a cormorant plunges into the ocean to catch a fish, it can change the refractive power of its eyes by about 45 diopters, as compared to only 16 diopters of change possible in the human eye.

a. Should this change of 45 diopters be an increase or a decrease?


b. If the focal length of the cormorant's eyes is 4.2 before it enters the water, what is the focal length after the refractive power changes by 45 diopters?

Explanation / Answer

a) increase

B) diopter= 1/focal length in meters
4.2mm=0.0042m=f
1/f=diopter=1/0.0042m=238 diopters
238 diopters+45 diopters=283 diopters
1/283m=3.53*10^-3m= 3.53m= new focal length

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