  It is general wisdom that likely charged colloidal particles repel each other
when suspended in liquids. This is in perfect agreement with mean field
theories being developed more than 60 years ago. Accordingly, it was a big
surprise when several groups independently reported long-ranged attractive
components in the pair potential U(r) of equally charged colloids. This
so-called like-charge attraction (LCA) was only observed in thin sample cells
while the pair-interaction in unconfined suspensions has been experimentally
confirmed to be entirely repulsive. Despite considerable experimental and
theoretical efforts, LCA remains one of the most challenging mysteries in
colloidal science. We experimentally reinvestigate the pair-potential U(r) of
charged colloidal particles with digital video microscopy and demonstrate that
optical distortions in the particles images lead to slightly erroneous particle
positions. If not properly taken into account, this artefact pretends a minimum
in U(r) which was in the past misleadingly interpreted as LCA. After correcting
optical distortions we obtain entirely repulsive pair interactions which show
good agreement with linearized mean field theories.
