(1) When the light passes through the slit, it is not within the diffraction range, so at this time, the light propagates along a straight line, and the slit width is reduced, so the light spot is also reduced;

(2) When the slit width is small enough to diffract light, the light does not propagate in a straight line, but diffracts. At this time, if the light spot continues to decrease, it can be seen from the diffraction characteristics that the range of light spot stripes will become larger, that is, the light spot will become larger.

So the light spot should be smaller first and then bigger.