Canon EOS40D AF-Assist Beam with the Built-in Flash, Lens’ Maximum Aperture and AF Sensitivity

SSelecting the AF PointN

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 the external, EOS-dedicated Speedlite’s AF-assist beam, select the center AF point.

AF-Assist Beam with the Built-in Flash

Under low-light conditions, when you press the shutter button halfway, the built-in flash fires a brief burst of flashes. It illuminates the subject to enable easier autofocusing.

In the <3> <5> <7> modes, the AF-assist beam does not fire. The built-in flash’s AF-assist beam is effective up to about 4 meters/13.2 feet.

In the Creative Zone modes when you pop-up the built-in flash with the <I> button, the AF-assist beam will be fired when necessary.

Lens’ Maximum Aperture and AF Sensitivity

With lenses whose maximum aperture is larger than f/5.6 With all AF points, cross-type AF sensitive to both vertical and horizontal lines is possible.

With lenses whose maximum aperture is larger than f/2.8*

With the center AF point, high-precision, cross-type AF sensitive to both vertical and horizontal lines is possible. The center AF point’s sensitivity to vertical and horizontal lines is about twice as sensitive as the other AF points.

The remaining eight AF points will work as cross-type points with lenses brighter than f/5.6.

* Except with the EF 28-80mm f/2.8-4L USM and EF 50mm f/2.5 Compact Macro lenses.

79