Canon UK has indicated on a support page that the Canon 7D, 60D, 50D and 40D have AF problems with certain older Canon EF zoom lenses.
When using any of eight zoom lenses listed below released between 1990 and 1995 with any of the listed cameras, the peripheral AF points do not function as cross-type AF points resulting in vertical and horizontal lines not being simultaneously detected. Vertical or horizontal lines can only be detected separately.
The affected lenses are as follows:
- EF 35-80mm f/4-5.6
- EF 35-80mm f/4-5.6 II
- EF 35-80mm f/4-5.6 III
- EF 35-80mm f/4-5.6 USM
- EF 35-105mm f/4-5.6
- EF 35-105mm f/4-5.6 USM
- EF 80-200mm f/4.5-5.6 II
- EF 80-200mm f/4.5-5.6 USM
Canon notes the cause of the problem as follows:
This is due to the optical characteristics of the camera’s AF sensor and lens. If the maximum aperture of the EF lenses and EF-S lenses other than the lenses above is up to f5.6, all of the AF points function as cross-type AF points, and both vertical and horizontal lines are simultaneously detected.
[via Canon UK]