Calculations with Optical Instruments
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.
P = 1 / f
Glasses strength = 1/(reading distance in meters) - 1/(minimal seeing distance in meters)
Calculation of focal length, optical power and diopter of glasses and the estimation of the right strength of reading glasses. These calculations are those for the basic properties of glasses. In fact, there is of course a lot more to say about glasses. There are bifocal lenses with two different prescription strengths per lens and the more modern progressive lenses with several, seamlessly merging strengths. Progressive lenses have developed into freeform lenses, which are made individually for the eyes of the person concerned based on complex measurements and calculations. Please refer to the appropriate optical specialists for this. The same applies to the question of when glasses are useful or helpful and what type they should be. Lenses can be made of mineral glass or plastic, both materials have certain advantages and disadvantages. The shape and size of the lenses must also be taken into account individually.