  We explore a new technique to measure cosmic shear using Einstein rings. In
Birrer et al. (2017), we showed that the detailed modelling of Einstein rings
can be used to measure external shear to high precision. In this letter, we
explore how a collection of Einstein rings can be used as a statistical probe
of cosmic shear. We present a forecast of the cosmic shear information
available in Einstein rings for different strong lensing survey configurations.
We find that, assuming that the number density of Einstein rings in the COSMOS
survey is representative, future strong lensing surveys should have a
cosmological precision comparable to the current ground based weak lensing
surveys. We discuss how this technique is complementary to the standard cosmic
shear analyses since it is sensitive to different systematic and can be used
for cross-calibration.
