Kombinera förstoringsglas

The simplest case is where lenses are placed in contact: if the lenses of focal lengths f1 and f2 are "thin", the combined focal length f of the lenses is given by

{\displaystyle {\frac {1}{f}}={\frac {1}{f_{1}}}+{\frac {1}{f_{2}}}.}{\frac {1}{f}}={\frac {1}{f_{1}}}+{\frac {1}{f_{2}}}.

Since 1/f is the power of a lens, it can be seen that the powers of thin lenses in contact are additive.