Originally Posted by drabina
So I got a crazy idea of switching brands and going for Nikon D80. I know that this is Pentax forum but I thought that somebody may have used D80 and knows how does this camera compares to K10D in terms of AF.
Even though the Nikon D80 AF is faster than the K10D (mainly at lower light levels, at bright levels the K10D is faster) -
it is still not instantaneous,
or even faster than
human reaction time (<0.2sec).
Lots of photographers manage to catch fast action and fleeting expressions with manual focus lenses - long before any AF
(and AF is
MUCH faster than we can focus manually) -
how? because they do
not try to focus only when they see the shot.....
What they did was to pre-focus their lens and wait for the shot - then trip the shutter - then it's down to only the shutter delay/lag itself, which is normally about 0.1sec.
With AF the technique remains basically the same -
Pre-Focus (half depression of shutter button and hold the focus) on a spot where the action/expression is likely to occur -
and when you see the shot fully depress the shutter -
then the delay is only about 0.1 sec -
which faster than human reaction time -
and certainly faster than
ANY known AF Nikon, Canon or otherwise......
FWIW - Popular Photography is one of the few places where they actually test AF speed over a range of light levels -
from:
Camera Test: Pentax K10D 
from:
Camera Test: Nikon D80 ... from:
Camera Test: Pentax K20D 
...

note: scale of horizontal axis of the K20D is misaligned - it should be the same as the Nikon D80