  The magnitudes of beam shifts (Goos-H\"anchen and Imbert-Fedorov, spatial and
angular) are greatly enhanced when a reflected light beam is postselected by an
analyzer, by analogy with superweak measurements in quantum theory.
Particularly strong enhancements can be expected close to angles at which no
light is transmitted for a fixed initial and final polarizations. We derive a
formula for the angular and spatial shifts at such angles (which includes the
Brewster angle), and we show that their maximum size is limited by higher-order
terms from the reflection coefficients occurring in the Artmann shift formula.
