Page 80 - (DK) Advanced Photography Guide

78 INTRODUCING |

FOCUSING

Despite the technical ingenuity of modern cameras and lenses, it is still

frustratingly easy to shoot blurry photos. Accurate focusing is the key to

overcoming this problem, and it helps to understand both the strengths
and weaknesses of a camera’s autofocus (AF) system so that you know which

options are best for any situation. It also helps you to decide when you would

get more accurate and consistent results by switching to manual focus (MF).

AUTOFOCUS SYSTEMS

There are two different AF systems used in cameras. DSLRs inside the lens (or via the camera body in the case of older AF
use phase detection through the viewfinder, while compacts, lenses) that move the lens optics to the right position so that
bridges, and CSCs use contrast detection, which is also the image is in focus. Both systems have their advantages and
employed in DSLR Live View. The AF systems drive motors disadvantages in terms of speed and accuracy.
PHASE DETECTION SYSTEM

The reflex mirror in a DSLR is partially translucent to allow light in the system—the lens, mirrors, and the AF module—must be
from the lens to be directed to a secondary mirror and, from precisely aligned. Any manufacturing fault or misalignment due
there, down to a phase-detection AF module. Phase-detection to damage will result in focusing errors, which some DSLRs can
AF is extremely fast and largely accurate, but every component compensate for with lens calibration (see p.81).

KEY TO ANNOTATIONS
10
1 Viewfinder eyepiece
2 Focusing screen
8 9 1
3 Digital sensor and shutter
4 Reflex mirror
2
5 Secondary mirror
3
6 AF module
4
7 Subject
8 Light rays 5
9 Lens optics 6
10 Pentaprism
7

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