Focusing Systems

Floating System
Extending the focusing lens group at close focusing distances can sometimes cause distortions such as curvature of field – particularly noticeable with wide-angle lenses. Canon counteracts this problem by incorporating 'floating' lens elements into many EF lenses. Because the floating component is separate to the focusing lens group, aberrations caused by lens extensions are significantly reduced. This means you can be sure of high image quality at all focusing distances.

Inner and Rear Focusing System
Many photographic lenses use either all-group focusing (all lens groups are moved together along the optical axis) or front-group focusing (only the front lens group is moved). These systems require far more power from the drive mechanism, limiting auto focus speeds. The need for large front lens groups also limits the potential for compact lens sizes.

The majority of Canon's lenses use inner focusing systems (placing the focusing lens group between the front lens and diaphragm) or rear focusing systems (placing the focusing lens group behind the diaphragm). These systems contribute to more compact lens sizes, rapid auto focusing and shorter minimum shooting distances. Lenses are also easier to handle since they do not change length during focusing. And because the front frame of these lenses does not rotate, polarizing filters are easier to use.

Click here to find out more about the Canon EF Lens Range and Technology.