As the mask is moved further, more electrons can travel through both slits, changing the
pattern from single-slit to double-slit diffraction. When the mask is centered on the double-slit,
both slits are completely open and full double-slit diffraction can be observed (P12 in figures 1(c)
and 2). In this position, interaction between the mask and the diffracting electrons is negligible.
The edges of the mask are 2250 nm away from the center and would only affect diffraction
orders greater than the 50th. The mask is then moved further and the reverse happens; doubleslit
diffraction changes back to single-slit diffraction (P2 in figures 1(b) and 2). Now, the singleslit
diffraction pattern has a weak contribution of double-slit diffraction in its positive first order
(see right edge of P2 in figure 2). (See supplementary movie 1 for more positions of the mask.)