I. CAMERA FEATURESAND OPERATION 13
focusing pointsresults in faster manual selection, and linking spot metering to the
manuallyselected focusing point comes in handy under certain circumstances,
particularlywith off-center subjects.
•C.Fn 13-2 also reducesthe number of manually selectable focusing points to 11, just
like C.Fn 13-1, exceptthat spot metering is fixed at the center of the frame. Locking
spotmetering at the center can be desirable, especially in Manual exposure mode,
because itallows the separation of focusing and metering.
•C.Fn 13-3 reduces the number of manually selectable focusing points to 9; 8 around
the periphery ofthe Area AF ellipse plus the center focusing point. This is a useful
option for sportsphotographers, because the peripheral focusing points can be
selected rapidlyvia the Quick Control Dial.
Custom Function 17allows the photographer to create a cluster of active focusing
pointsduring manual focusing point selection.
•C.Fn 17-0 forces the camera to evaluate only the manually selected focusing point or
points. Thisis often the best choice when working with average subjects.
•C.Fn 17-1 expands the active focusing area by a radius of 1 point around the manually
selected focusing point, creating up to 7 active focusing points. The camera always
triesto use the manually selected focusing point, but when it can’t, it can choose one
ofthe other 6 active focusing points if there is readable subject detail under one of
them. Thisoption is intended to increase the odds of getting sharp photos with small,
fastmoving subjects such as birds in flight. However, it can sometimes cause critical
focusto shift slightly ahead of or behind relatively large 3-dimensional subjects like
human beings. We suggestpracticing with C.Fn 17-1 repeatedly until you get a feel for
whatit can and cannot do in your specific applications.
•C.Fn 17-2 performsa little differently according to the camera model. With the original
EOS-1D and EOS-1Ds, the camera decideswhether or not to expand the focusing area
bya radius of 1 or 2 focusing points around the manually selected focusing point
based on the focallength of the lens in use as well as the subject’s degree of
movement. The photographer hasno control over it other than lens selection. With the
MarkII cameras, on the other hand, C.Fn 17-2 expands the active focusing area by a
radiusof 1 point around the manually selected focusing point at focal lengths up to
200mm, or bya radius of 2 points when the focal length is greater than 200mm,
regardlessof the degree of subject movement.
Note:In theory, Custom Function 17-1 or 17-2 slightly reduces AF speed because of the
extra calculationsinvolved. However, expanding the active focusing area often
increasesthe odds of finding a readable subject when subject size is small, or low in
contrast. We encourage you to experimentwith all C.Fn 17 settings to determine which
setting isbest for your specific needs.
Custom Function 18programs the functions of the Assist Button near the eyepiece of
the camera.