Canon EOS 5D Mark III EOS 5D Mark III Instruction Manual - Page 211

Using AF to Focus Shooting conditions that can make focusing difficult Low-contrast subjects such as the blue sky and solid-color, flat surfaces. Subjects in low light. Stripes and other patterns where there is contrast only in the horizontal direction. Under a light source whose brightness, color, or pattern keeps changing. Night scenes or points of light. Under fluorescent or LED light sources or when the image flickers. Extremely small subjects. Subjects at the edge of the picture. Subjects strongly reflecting light. The AF point covers both a near and faraway subject (such as an animal in a cage). Subjects that keep moving within the AF point and cannot keep still due to camera shake or subject blur. A subject approaching or moving away from the camera. Autofocusing while the subject is way out of focus. Soft focus effect is applied with a soft focus lens. A special effects filter is used. If you use AF with any of the following lenses, using [Quick mode] is recommended. If you use the [Live mode] or [u Live mode] for AF, it may take a longer time to achieve focus or the camera may not be able to achieve correct focus. EF24mm f/2.8, EF35mm f/2, EF50mm f/2.5 Compact Macro, EF100mm f/2.8 Macro, EF135mm f/2.8 (Softfocus), EF28-90mm f/4-5.6 III, EF55200mm f/4.5-5.6 USM, EF90-300mm f/4.5-5.6, EF90-300mm f/4.5-5.6 USM 211