Pls explain lamda / 20 in radio telescope mech

Question: Pls explain lamda / 20 in radio telescope mech
- Keywords:
  lamda 20,
  radio telescope
Asked by YungTingShirley to Hermine on 18 Mar 2018.
- Hermine Schnetler answered on 18 Mar 2018:
  
  I think you are referring to the required smoothness of a parabolic dish antenna. Thus it implies that the surface r.m.s error of a parabola typically should be less than lambda/20, which is basically the rule of thumb to make the error negible.

Question: Pls explain lamda / 20 in radio telescope mech