Canon EOS-1 - Manual (Page 13)

I. CAMERA FEATURES AND OPERATION 13
focusing points results in faster manual selection, and linking spot metering to the
manually selected focusing point comes in handy under certain circumstances,
particularly with off-center subjects.
• C.Fn 13-2 also reduces the number of manually selectable focusing points to 11, just
like C.Fn 13-1, except that spot metering is fixed at the center of the frame. Locking
spot metering at the center can be desirable, especially in Manual exposure mode,
because it allows the separation of focusing and metering.
• C.Fn 13-3 reduces the number of manually selectable focusing points to 9; 8 around
the periphery of the Area AF ellipse plus the center focusing point. This is a useful
option for sports photographers, because the peripheral focusing points can be
selected rapidly via the Quick Control Dial.
Custom Function 17 allows the photographer to create a cluster of active focusing
points during manual focusing point selection.
• C.Fn 17-0 forces the camera to evaluate only the manually selected focusing point or
points. This is 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
tries to use the manually selected focusing point, but when it can’t, it can choose one
of the other 6 active focusing points if there is readable subject detail under one of
them. This option is intended to increase the odds of getting sharp photos with small,
fast moving subjects such as birds in flight. However, it can sometimes cause critical
focus to shift slightly ahead of or behind relatively large 3-dimensional subjects like
human beings. We suggest practicing with C.Fn 17-1 repeatedly until you get a feel for
what it can and cannot do in your specific applications.
• C.Fn 17-2 performs a little differently according to the camera model. With the original
EOS-1D and EOS-1Ds, the camera decides whether or not to expand the focusing area
by a radius of 1 or 2 focusing points around the manually selected focusing point
based on the focal length of the lens in use as well as the subject’s degree of
movement. The photographer has no control over it other than lens selection. With the
Mark II cameras, on the other hand, C.Fn 17-2 expands the active focusing area by a
radius of 1 point around the manually selected focusing point at focal lengths up to
200mm, or by a radius of 2 points when the focal length is greater than 200mm,
regardless of the degree of subject movement.
Note: In theory, Custom Function 17-1 or 17-2 slightly reduces AF speed because of the
extra calculations involved. However, expanding the active focusing area often
increases the odds of finding a readable subject when subject size is small, or low in
contrast. We encourage you to experiment with all C.Fn 17 settings to determine which
setting is best for your specific needs.
Custom Function 18 programs the functions of the Assist Button near the eyepiece of
the camera.