704 Interamnia
Its very dark surface and fairly far distance from the Sun means Interamnia can never be seen with 10x50 binoculars. At most oppositions its magnitude is around +11.0, which is less than the minimum brightness of Vesta, Ceres or Pallas. Even at a near-perihelion opposition its magnitude is only around +9.9, which is over four magnitudes lower than Vesta.