  A minimal solution using two affine correspondences is presented to estimate
the common focal length and the fundamental matrix between two semi-calibrated
cameras - known intrinsic parameters except a common focal length. To the best
of our knowledge, this problem is unsolved. The proposed approach extends point
correspondence-based techniques with linear constraints derived from local
affine transformations. The obtained multivariate polynomial system is
efficiently solved by the hidden-variable technique. Observing the geometry of
local affinities, we introduce novel conditions eliminating invalid roots. To
select the best one out of the remaining candidates, a root selection technique
is proposed outperforming the recent ones especially in case of high-level
noise. The proposed 2-point algorithm is validated on both synthetic data and
104 publicly available real image pairs. A Matlab implementation of the
proposed solution is included in the paper.
