American Board of Opticianry (ABO) Practice Test

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What is the focal length of a +4.00 diopter lens?

15 cm
25 cm
35 cm
45 cm

The correct answer is: 25 cm

The focal length of a +4.00 diopter lens is 25 cm. Diopters are a unit of measurement used to describe the optical power of a lens, and they are equal to the reciprocal of the focal length measured in meters. As the diopter value increases, the focal length decreases, resulting in a more strongly converging lens. Therefore, options A, C, and D are incorrect because they have larger focal lengths and lower diopter values. In contrast, option B has a smaller focal length and a higher diopter value, making it the correct answer.