AF (Auto Focus) can fail to achieve focus (the focus confirmation light blinks) on certain subjects such as the following:

(a) Low-contrast subjects.
e.g. blue sky, solid-colour walls

(b) Subjects in low light.

(c) Extremely backlit reflective subjects.
e.g. a car with a reflective body

(d) Overlapping near and far objects.
e.g. an animal in a cage

In cases such as these, do one of the following:

1. Focus on an object at the same distance as the subject and lock the focus before recomposing.

2. Set the lens focus mode switch to < MF> and focus manually.