研究了一下manual,发现5D2跟7D的中心点对焦在小于F2.8时应该是一样的,
两者在F5.6时都是中心十字(非高精)对焦。
可能的区别是在F2.8时,7D中心应该是双十字高精对焦(5D2是十字高精)。
所以在7D或5D2上用xxb, 540等一系列F4.0的镜头,两者对焦精度应该一样,
只有1D系列机身,在F4仍然是高精对焦。
所以,镜头最大光圈小于F2.8并只用中心对焦的时候,在5D2和7D难道不是一样的?
除非我还miss了什么。
以下摘自Canon manual
【【5D2】】:
【With lenses whose maximum aperture is larger than f/5.6】
With the center AF point, cross-type AF (sensitive to both vertical and
horizontal lines) is possible. The remaining eight AF points are
horizontal-line sensitive or vertical-line sensitive.
【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 are horizontal-line sensitive
or
vertical-line sensitive
【【7D】】:
【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. Note that with certain lenses (p.263), the
peripheral AF points will be vertical-line or horizontal-line sensitive
only
(They will not work as cross-type points).
【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 18 AF points will work as cross-type points with lenses
brighter than f/5.6.
【【1Ds3】】:
【With f/2.8 and faster lenses】
With the 19 AF points indicated by ,
high-precision, cross-type AF (both
horizontal- and vertical-line sensitive) is
possible. With cross-type AF, vertical-line
detection is about 2 times as sensitive as
horizontal-line detection. The remaining
26 Assist AF points are horizontal-line
sensitive only.
【With lenses whose maximum aperture is f/4 or larger】
If the maximum aperture of the lens or Extender and lens combination
is faster than f/4, the center AF point will work as a high-precision,
cross-type point sensitive to both horizontal and vertical lines. The
remaining 18 AF points and the 26 Assist AF points work as
horizontalline
sensitive AF points.
【With lenses whose maximum aperture is f/5.6 or larger】
With lenses whose maximum aperture is larger than f/5.6, all the AF
points, including the Assist AF points, will be horizontal-line
sensitive
only.
With lenses whose maximum aperture is f/8 or larger
With lenses whose maximum aperture is larger than f/8, AF will be
possible with the center AF point which will be horizontal-line
sensitive.
AF will not work with the other AF points.