  An ideal coronagraph with a band-limited image mask can efficiently image
off-axis sources while removing identically all of the light from an on-axis
source. However, strict mask construction tolerances limit the utility of this
technique for directly imaging extrasolar terrestrial planets. We present a
variation on the basic band-limited mask design--a family of ``notch filter''
masks--that mitigates this problem. These robust and trivially achromatic masks
can be easily manufactured by cutting holes in opaque material.
