  The response field of a half-space anisotropic superconductor is evaluated
for an arbitrary weak external field source. Example sources of a point
magnetic moment and a circular current are considered in detail. For the
penetration depth $\lambda \ll L$ with $L$ being any other relevant distance
(the source size, or the distance between the source and the superconductor),
the major contribution to the response is the $\lambda$ independent field of
the source image. It is shown that the absolute value of $\lambda$ cannot be
extracted from the response field with a better accuracy than that for the
source position. Similar problems are considered for thin films.
