Intermediate Photography Lesson 2 Quiz | Test Your Knowledge

At 1/1000 second the motion is frozen, so the blur is a focus problem, not a movement problem. AF-S sets focus once when the button is half pressed and then holds it, so a dog running toward you leaves the plane of focus before the shutter fires. Continuous AF (AF-C) keeps refocusing as it moves.

Single-point AF lets you put focus exactly on the nearest eye, which is where viewers look first. Wide-area and zone modes let the camera choose, and they often pick the nose, eyebrows or a shoulder instead. At wide apertures, that small miss is enough to leave the eye soft.

Back button focus moves autofocus to a rear button, so the shutter button only takes the picture. With continuous AF set, holding the rear button tracks a moving subject, and letting go locks focus for a still one. You switch behavior with your thumb instead of changing AF modes.

Autofocus tends to grab the nearest strong edges, and a fence in front of the bird provides plenty. Manual focus lets you set focus on the bird yourself, and a wide aperture then blurs the wires so they nearly disappear. A smaller aperture would make the fence sharper, not hide it.

With AF-S the focus distance locks when you half-press. Turning the camera to recompose swings the plane of focus, so with a wide aperture and a thin depth of field the face ends up just outside it. Moving the AF point onto the face instead of recomposing avoids this.

Zone focusing means setting the lens to a fixed distance and using a fairly small aperture, such as f/8, so a band of distances in front of and behind that point stays acceptably sharp. You can then shoot instantly without waiting for autofocus, which is why it suits street photography.

Autofocus needs light and contrast, and in a very dim room it hunts. Manual focus with focus peaking or a magnified view lets you confirm sharpness yourself. Holding the half-press longer does not add light, and wide-area AF has the same problem.

A common handheld guide is a shutter speed of at least 1 over the focal length, about 1/50 second for a 50mm lens, and high-resolution sensors need faster still. At 1/30 second, small hand movements smear the whole image even when focus is correct. A faster shutter, stabilization or a support fixes it.

Focusing at the hyperfocal distance puts the far limit of depth of field at infinity while bringing the near limit as close as possible, about half that distance. That gives the greatest front-to-back sharpness for the focal length and aperture in use. Focusing on the horizon wastes depth of field beyond infinity.

Eye detection finds eyes, but it cannot know which of many people you care about. In a crowd at different distances it may jump between faces or lock onto the nearest one. A single person facing the camera, with or without glasses, is the case it handles best.