Tamron SP 200-500mm f/5.6 (Model 31A) adaptall lens was designed for superior off-axis performance rather than for compactness. The zoom group uses four elements for the variator group and three elements for the compensator group. This seven element zoom group design allowed Tamron's optical engineers to firmly control off-axis aberrations. The SP 200-500mm is capable of close focusing to 8.2 feet for a 1:3.52 maximum magnification ratio, but the lens will exhibit moderate amounts of spherical aberration at very close focus distances. Close focusing induced spherical aberration is greatly minimized by F/11.