What is the meaning of saying " the plwer of lens is 1 dioptre"?

1 Answer
MeneerNask
Jun 21, 2018

A lens is more powerful as the focal length decreases.

Explanation:

This was thought contra-intuitive, to have a smaller number for a stronger lens. So they created a new measure: the diopter, or 'power' of a lens is defined as the inverse of the focal length, or:

#D=1/f# with #f# in meters, or #D=1000/f# with #f# in millimeters.

The reverse is also true: #f=1/D# or #f=1000/D#, depending on the use of meters or mm.

So a lens with a 'power'of 1 Diopter has a focal length of:

#f=1/1=1m# or #f=1000/1=1000mm#

A standard #50 mm# camera lens will have a 'power' of:

#D=1000/50=20# diopter.

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