In this letter , we exploit the gravitational potential of the rich cluster A 2218 as a magnifying glass .
We demonstrate that the magnification due to the cluster allows us to observe distant background galaxies at a comparable level of detail to galaxies at z \sim 0.1 .
Using the GMOS Integral Field Unit on Gemini North we observed the spatially-resolved [ O ii ] \lambda 3727 emission line spectrum for a lensed disk-galaxy at z=1.034 .
Using a detailed model for the cluster mass distribution , we are able to correct for the lensing by the cluster and reconstruct the source morphology .
We find that the overall magnification is a factor of 4.92 \pm 0.15 , and the rest-frame absolute I -band magnitude is M _ { I } ^ { rest } = -22.4 \pm 0.2 , where the error bars include conservative estimates of the uncertainty in the source-plane reconstruction .
The inclination-corrected circular velocity is 206 \pm 18 \hbox { km } \hbox { s } ^ { -1 } .
The galaxy lies very close to the mean Tully-Fisher relation of present-day spirals .
Although our results are based on a single object , they demonstrate that gravitational lensing can be viably used to make detailed studies of the evolution of the structure of distant field galaxies .