The optics of the EF 90-300mm f/4.5-5.6 are based on those of the EF 75-300mm f/4-5.6 III and the optical performance is similar. However, the AF drive pattern has been optimized for the EOS 300V, giving a faster AF speed. Also, a new AF algorithm has been developed. All the lens elements are manufactured from environmentally-friendly lead-free glass. A redesigned electromagnetic diaphragm (EMD) provides an aperture which is nearly circular at the widest settings. This gives an improved out-of-focus background effect.