  Advances in upcoming weak lensing surveys pose new challenges for an accurate
modeling of the lensing observables. With their large sky coverage, common
approximations based on a flat-sky geometry cannot be used anymore to evaluate
all measurable angular scales. Moreover, additional relativistic effects
manifest themselves on large scales and thus need to be accounted for. In
particular, the lensing magnification cannot be correctly described by the
standard lensing convergence only. We present the analytical solutions for the
fully-relativistic weak lensing angular power spectra, including the
contribution from primordial gravitational waves. We compare the results
obtained by using the Limber approximation with the precise all-sky
calculations using spherical harmonics. Our numerical evaluations show that
general relativistic corrections are one order-of-magnitude below cosmic
variance at small scales ($l\geq 10$). At large scales ($l<10$), however,
neglecting them leads to more significant errors, especially when combined with
the Limber approximation. Hence, a precise, fully-relativistic modeling is
necessary at these largest scales.
