Autofocus can fail to achieve focus (the focus confirmation light <> blinks) with certain subjects such as the following:

• Low-contrast subjects (blue sky, solid-color walls, etc.).
• Subjects in low light.
• Extremely backlit and reflective subjects (car with a reflective body, etc.).
• Overlapping near and far objects (animal in a cage, etc.).
• Lens and/or external AF sensor is dirty

In such cases, do one of the following:

1. Focus 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.
3. Ensure that the lens and any external sensors on the camera are clean. If necessary they may be cleaned with a soft cloth.