A monochromatic light beam of wavelength λ is
s0k qlsri; go*,0z2kpdiffracted at a single slit of width
ki*;z qp k2gsr0,0lso $b$. After passing the slit, a diffraction pattern is observed on a screen a large distance away. The width of the central maximum is $w$.
The screen is moved closer to the slit. Which of the following changes, done separately, could result in no change in $w$?