5.4.1 Effects due to space curvature
Globally, the angular extent of an object seen at a given distance r depends on redshift z and on the cosmological parameters.
Local effects on the light path may become apparent in gravitational lensing, where the angular sizes can grow up to 2. Other local effects can generally be neglected.
The corrections mentioned in Sect. 5.3 also apply to angular measurements, where aperture effects may be present and central absorption discs at large inclinations may mask the outer parts of the galaxies.