The magnification ratio of a lens describes the maximum size at which an object can be reproduced on the camera’s sensor. For example, if an object is 1cm long, and a lens can photograph it so that the impression on the sensor is also 1cm long, the magnification ratio is said to be 1:1. If the impression on the sensor were 0.5cm, the magnification ratio would be 1:2. Sigma’s macro lenses are true macro because they have a 1:1 magnification ratio.