358CHAPTER 25 (b) If the object distance must be 26.0 cmp=to position the image at , the actual focal length is 75.0 cmq=−()( )26.0 cm75.0m26.0 cm75.0pqfpq−==+−cm0.398cm=and 112.510.398 mf=+P(diopters The error in the power is )2.672.51 diopter∆=−Ps0.16 diop=ters too low 25.50(a) If q=when , the thin lens equation gives the focal length as 2.00 cm1.00 m100 cmp100 ccm100 cmpqfm2.00 cm1.962.00 cm=++(b) The f-number of a lens aperture is the focal length of the lens divided by the diameter of the aperture. Thus, the smallest f-number occurs with the largest diameter of the aperture. For the typical eyeball focused on objects 1.00 m away,
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