Manual focus is the direct control of a camera/lens's focus by the photographer. This is generally accomplished by turning a focus ring which is mechanically coupled to the lens's focus, but some cameras without focus rings allow manual control over the autofocus motor.
I'm using two cameras: Canon EOS 400D (Digital Rebel XTi) and Canon EOS 450D (EOS Rebel XSi). 450D was more heavily used than 400D. Not so long ago I noticed that 450D's autofocus system works not ...