Focal Length is reciprocal of the Diopter. It means, Zero Diopter , Plano, has Focal Length of Infinity. Now, I am going to write the Diopter n Focallength in Meter values as 'D/F '. 0.25/4 , 0.5/2 , 0.75/1.33 , 1/1 , now, the focal length is being written in centimeter. 1.25/80, 1.5/66.6, 1.75/57.41, 2/50 ,2.5/40, 3/33.33, 4/25. 5/20, 6/16.66 7/14.285, 8/12.5, 9/11.11 , 10/10, 11/9.0909 12/8.33 . Kindly notice, for change in Diopter from 1 to 2, the Focal Length changed from 1 meter to 50 cms, (Change of 50 cms) . But, for change of 11 to 12, focal length changes merely by 0.75 cm ! Let us try to understand the meaning. When a 0.25 sph. Lens gives 6/6 vision, its changing the Focal Length by 4 meters. When a 12 diopter lens achieve 6/6,focal length changes by just 8.33 cms. The lens pricing should be based up on the Focal Length. More the focal length, more should be price. The Rxs should also be written in meters and not diopters..Good change for recession !
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