A monochromatic light beam of wavelength λ
lxlv lq op:n3lv8-+ 0u is diffracted at a single slit of width
+q :nx3ol puv-0l l8vl $b$. 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 $w$?