What should I do if the autofocus fails to achieve focus?

If the focus confirmation light blinks, autofocus has failed, which can happen with low-contrast subjects, subjects in very low light, extremely backlit or reflective subjects, or subjects with repetitive patterns. You can use focus lock by focusing on an object at the same distance as the subject and recomposing, or set the lens focus mode switch to MF and focus manually by turning the lens focusing ring. (Page 31)