  A perturbative method to compute the deflection angle of both timelike and
null rays in arbitrary static and spherically symmetric spacetimes in the
strong field limit is proposed. The result takes a quasi-series form of
$(1-b_c/b)$ where $b$ is the impact parameter and $b_c$ is its critical value,
with coefficients of the series explicitly given. This result also naturally
takes into account the finite distance effect of both the source and detector,
and allows to solve the apparent angles of the relativistic images in a more
precise way. From this, the BH angular shadow size is expressed as a simple
formula containing metric functions and particle/photon sphere radius. The
magnification of the relativistic images were shown to diverge at different
values of the source-detector angular coordinate difference, depending on the
relation between the source and detector distance from the lens. To verify all
these results, we then applied them to the Hayward BH spacetime, concentrating
on the effects of its charge parameter $l$ and the asymptotic velocity $v$ of
the signal. The BH shadow size were found to decrease slightly as $l$ increase
to its critical value, and increase as $v$ decreases from light speed. For the
deflection angle and the magnification of the images however, both the increase
of $l$ and decrease of $v$ will increase their values.
