The Fraunhofer diffraction pattern of an aperture formed between a kni
fe edge and a smooth surface of a turned metal cylinder or half cylind
er is different from the diffraction pattern of an ideal slit aperture
. The diffraction pattern is simulated by adding the light reflected b
y the cylinder surface to the pattern formed by a slit, and is measure
d using a cylinder that has been partly cut away so that it can repres
ent either a full or half cylinder. The theoretical and measured patte
rns agree well with each other.