Tamron 28-50mm f3.5-4.5 CF Macro is an ultra-compact continuous focusing (CF) standard zoom lens. The extremely compact optical design reduces distortion at the wide angle settings and produces virtually zero distortion at the 50mm setting. Optical performance at 28 mm is very good at F/8, yet remains slightly soft in the corners. Optical performance from 37mm to 50mm is very good across the field by F/5.6, with much better corner sharpness as well. Macro performance reaches a 1:5 reproduction ratio at the 50mm setting.