Canon EOS 20D EOS 20D Instruction Manual - Page 68

SSelecting the AF PointN Selecting with the Dial ¡ Press the and turn the or dial. ¡ When you turn the dial, the selection will go in the looping sequence shown on the left. ¡ When looking at the LCD panel to select the AF point, note the following: Automatic selection , center , right , top ¡ If focus cannot be achieved with an EOS-dedicated, external Speedlite's AF-assist beam, select the center AF point. AF-Assist beam with the Built-in Flash Under low-light conditions, the built-in flash fires a brief burst of flashes when you press the shutter button halfway. This is to illuminate the subject to enable easier autofocusing. ¡ In the modes, the AF-assist beam does not light. ¡ The built-in flash's AF-assist beam is effective up to about 4 meters/13.2 feet. ¡ In the Creative Zone modes when the built-in flash is popped up with the button, the AF-assist beam will be emitted if necessary. Lens' Maximum Aperture and AF Sensitivity The EOS 20D will execute high-precision AF with lenses whose maximum aperture is f/2.8 or larger. With lenses whose maximum aperture is f/2.8 or larger With the center AF point, high-precision, cross-type AF sensitive to both vertical and horizontal lines is possible. With cross-type AF, vertical-line detection is twice as sensitive as horizontal-line detection. The other eight AF points are horizontal-line sensitive or vertical-line sensitive. With lenses whose maximum aperture is larger than f/5.6 The center AF point is a cross-type AF sensor. The other eight AF points are horizontal-line sensitive or vertical-line sensitive. 68