  With magnetic force microscopy in mind, we study the unbinding transition of
individual flux lines from extended defects like columnar pins and twin planes
in type II superconductors. In the presence of point disorder, the transition
is universal with an exponent which depends only on the dimensionality of the
extended defect. We also consider the unbinding transition of a single vortex
line from a twin plane occupied by other vortices. We show that the critical
properties of this transition depend strongly on the Luttinger liquid parameter
which describes the long distance physics of the two-dimensional flux line
array.
