- It is argued that a precessing jet will, at some sufficiently large scale, be focused by an ambient plasma of finite pressure such that its angular spread on larger scales is much smaller than that of the precession cone at small scales. More generally, the collimation of a moderately wide jet can be sharpened by the ambient medium, and a smeared-out beam can be recollimated. Shapes of channels formed by such recollimated beams are calculated. The focal length along the precession axis is found to be nearly independent of the original opening angle if the other jet parameters are fixed. The results are compared with real sources where there is some observational evidence for jet focusing, such as SS 433.