| Front group rotational extension | The lens barrel section holding the front lens group rotates to move the front group backward and forward during focusing. This type of focusing is used only in zoom lenses and is not found in single focal length lenses. Representative examples of lenses using this method are the EF 35-80mm f/4-5.6 USM and EF 100-300mm f/5.6L. Since the filter attachment ring and hood rotate with the lens during focusing, care must be taken when shooting through a glass window to make sure the end of the lens does not contact the glass. |
