When should the focal length of the lens be larger: when looking at close or distant objects? How does the optical power of the lens change when looking at close objects in comparison with looking at distant objects – does it increase or decrease?
From the formula for a thin lens, it follows that with a decrease in the distance a from the lens to the object at a constant distance f from the lens to the image, the focal length F should also decrease. Therefore, when considering close objects, the focal length of the lens should be shorter. With a decrease in the focal length of the lens, its optical power, equal to 1 / F, increases.
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