  In the last decade, metamaterials-based superlenses, with a resolution below
Abbe's diffraction limit, have emerged. To obtain a rough estimate of the
resolution of such superlenses, imaging of two subwavelength slits, separated
by a subwavelength gap \textit{d} is typically performed. The resolution
$\Delta$ of the lens corresponds to the minimum possible gap $d_{min}$ for
which a distinct image of the two slits can be resolved ($\Delta \sim
d_{min}$). In this letter, we present a more quantitative estimate of the
resolution of manufactured lenses by fitting analytical near-field image
profiles, obtained from imaging a two-slit object with a theoretical
negative-index lens of known resolution, to experimental data. We conclude the
discussion by applying our analytical method to 3 case examples of superlensing
from the literature. As shown, this method is particularly attractive for
rapidly assessing the performance of fabricated superresolution lenses.
