Galaxies and clusters around and in front of radio sources at 0.5 < z < 4.5

Some recent work on radio source fields at z ~ 0.7 and z ~ 4 is discussed. At z ~ 0.7 we find that radio-loud quasars are typically found in moderately rich environments independent of radio luminosity, consistent with previous results at z ~ 0.5. In the field of the z = 4.41 radio galaxy 6C0140+326 we find several candidate z > 4 galaxies using the Lyman-break technique, two of which have detectable UV absorption features. In two z > 4 radio galaxies, we find evidence for gravitational lensing affecting the fluxes by a few tens of percent, although we cannot rule out unusual lensing events which have larger magnifications associated with them. A simple calculation suggests lensing of z > 4 radio sources should be very common.