Canon EF 75-300mm f/4.0-5.6 III Filter Size 58mm Zoom Lens (Not USM)The optical system, construction, and exterior are the same as the EF 75 300 mm f 4 5. 6 III USM. The difference is that it uses a DC motor instead of a USM to drive the AF This lens has the same optical system, construction, and exterior design as the EF 75 300mm f 4 5. 6 III USM lens however instead of having a USM, it has a micro motor.