<P> For a smooth zone plate, the opacity (or transparency) at a point can be given by: </P> <Dl> <Dd> 1 ± cos ⁡ (k r 2) 2 (\ displaystyle (\ frac (1 \ pm \ cos (kr ^ (2))) (2)) \,) </Dd> </Dl> <Dd> 1 ± cos ⁡ (k r 2) 2 (\ displaystyle (\ frac (1 \ pm \ cos (kr ^ (2))) (2)) \,) </Dd> <P> where r (\ displaystyle r) is the distance from the plate center, and k (\ displaystyle k) determines the plate's scale . </P>

Similarities and dissimilarities between zone plate and convergent lens