in article
5b818771-9c68-48b0-8b3a-cb3f61760252@[EMAIL PROTECTED]
at aniramca@[EMAIL PROTECTED]
wrote on 1/1/08 00:50:
> Or, I may miss something completely and more fundamental here?
The sensor points are not magic 'rangefinders' that output distances. They
are phase detection sensors. Some are 'cross type'- i.e they detect in two
planes at the same time.
See the following pages on Nikon's site:
http://preview.tinyurl.com/2mnrns
http://preview.tinyurl.com/36dj2z
There are many different focus modes on the D300:
€ Single point AF
€ Dynamic Area AF [9 points, 21 points, 51 points, 51 points
(3D-tracking)]
€ Automatic-area AF
I think in dynamic area mode, you can set whether it biases the choice to
closer subjects, or not. It will also automatically start focus tracking
(predicting where a subject will be, and focussing there before the
subject
reaches that point). Combine all these options with AF-S and AF-C modes,
and
you're looking at quite a few combinations of settings.
In Live View mode, it will use contrast detection AF on any desired point
in
the frame (i.e. change the focus, see if this increases contrast, if not,
go
the other way, etc.). All other AF modes won't work, as the focus sensors
are in the bottom of the mirror box, and they get their image from a
secondary mirror that reflects light from the middle of the frame (that
has
passed through the semi-silvered primary mirror). As the mirror is up
during
live view, this can't work. I think there is an Olympus live view method
where the live view comes from a second colour CCD in the prism housing,
and
so the mirror is down.
HTH,
Ben
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