Using a fixed focus point actually reduces the camera's ability to
follow focus in AF-C mode. The camera's programming, if it's like all
the other AF cameras with multipoint sensor systems that I have used,
uses the differential in focus discrimination between the sensors to
aid follow-focus accuracy.
For instance, with my 10D I get almost dead-on accuracy when follow
focus is enabled across the entire sensor range with a subject
crossing the field of view or coming at me at an angle.
Follow focus on a head-on approach is simply the hardest situation
for an AF system to manage because the discriminator changes very
very little in comparison to focus traversing the field of view. You
need ALL sensors active to do the best with it. Then factors of
response time and latency also have their effect.
Rule of thumb: close up situations with head-on movement are better
handled with manual focus and DoF than AF-C automation. This is true
for every AF camera I've used.
Godfrey
On Mar 20, 2006, at 4:15 AM, Mishka wrote:
yes, i had a fixed af point, in the center, and i tried to keep the
kid in the
center of the frame all the time. the lens can focus this close and
much closer
w/o any problems.
i looked at the exif data in the "swing" set of pics, and apparently,
in about 60%
of them, it shows "distant view" focus seting when the kid is at the
closest distance
and "close view" whe he's at the farthest point. so it's the matter of
af-c latency.
unfortunately it doesn't show the exact distance. my guess would be
~1m at the closest
and ~4m at the farthest, with swing period about 2s.
best,
mishka
On 3/20/06, Kostas Kavoussanakis <[EMAIL PROTECTED]> wrote:
On Sun, 19 Mar 2006, Mishka wrote:
thanks guys, for confirming what i suspected.
so much for "better living through electricity".
I agree with all the previous posters. I also add that you may have
been too close to focus, Auto or Manual, in which case AF-C just went
for what it could focus on.
Had you fixed the focussing point, or does your camera not offer
this?
Kostas
