Advances in high angular resolution astronomy make it conceivable that black hole dark matter could be detected via angular deviation effects. Assuming the dark matter in the galaxy is made of solar mass black holes, there is a nontrivial probability that a line-of-sight through the galaxy, leads to [Formula: see text]’s deviations, a value that has been discussed for various astronomical projects. In cosmology, the effects are magnified by an increased density at early times and an opening of angles due to redshift. We stress the interest of the resolution in observations on the CMB and emphasize the distinction between this and the power spectrum. If the dark matter is made of primordial black holes, present at the CMB, random deflections of the CMB photons lead to a limit on the angular resolution, approximately [Formula: see text] rad, with [Formula: see text] the mass of the black holes. Using the resolutions of [Formula: see text] demonstrated in observations of the “acoustic peaks” then implies the limit [Formula: see text]. While this large value seems uninteresting, improved resolutions would lead to significant exclusion limits or conceivably the discovery of primordial black holes.