With a redshift of z \approx 1.7 , SN 1997ff is the most distant type Ia supernova discovered so far .
This SN is close to several bright , z = 0.6 - 0.9 galaxies , and we consider the effects of lensing by those objects on the magnitude of SN 1997ff .
We estimate their velocity dispersions using the Tully-Fisher and Faber-Jackson relations corrected for evolution effects , and calculate , applying the multiple-plane lensing formalism , that SN 1997ff is magnified by 0.34 \pm 0.12 mag .
Due to the spatial configuration of the foreground galaxies , the shear from individual lenses partially cancels out , and the total distortion induced on the host galaxy is considerably smaller than that produced by a single lens having the same magnification .
After correction for lensing , the revised distance to SN 1997ff is m - M = 45.5 mag , which improves the agreement with the \Omega _ { M } = 0.35 , \Omega _ { \Lambda } = 0.65 cosmology expected from lower-redshift SNe Ia , and is inconsistent at the \sim 3 \sigma confidence level with a uniform gray dust model or a simple evolution model .