Calculations with Optical Instruments

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Glasses

Glasses are made of two lenses and a frame. The strength of glasses, their optical power, is measured in diopter (dbt), this value is the reciprocal of the lens focal length in meters. Convex (bend outward) lenses have a positive diopter value and correct farsightedness. Concave (bend inward) lenses have a negative diopter value and correct nearsightedness. Farsighted people see better at distances than at close objects, this is common in higher age.

Focal length f:		m
Optical power P:		dpt

P = 1 / f

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Strength of Reading Glasses for Farsightedness

Enter the average distance of your eyes from the text you want to read and the minimal distance where you can see clearly. The strength of the required reading classes is calculated. This is an estimation, ask your optician, which glasses you really need.

Reading distance:		cm
Minimal seeing distance:		cm
Glasses strength:		dpt

Glasses strength = 1/(reading distance in meters) - 1/(minimal seeing distance in meters)

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Calculation of focal length, optical power and diopter of glasses and the estimation of the right strength of reading glasses.

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