Julian Loke wrote:
> So, I'm still a bit confused. Would it be correct to conclude that the
> EOS 3 does not have vertical sensors at f/5.6?
That is the spec. I think it might be more accurate to say that you are unlikely
to get consistent vertical-line focusing with the 3 at maximum apertures of
f/5.6 or smaller (or perhaps even f/4 or smaller), because the 3 will continue
to attempt to focus at f/5.6, and may even succeed on occasion. This is
consistent with Canon's specification, which is that vertical-line focusing is
lost at maximum apertures of f/4 or smaller.
I now wish that I had kept a copy of what I wrote a little longer--I don't
remember what I said about the performance of the center sensor! And, did I say
that the horizontal-line sensors continued to work well at f/5.6? I seem to
recall that they did.
What remains intriguing is the question of what happens between max apertures of
f/4 and f/6.7. The EOS 3 manual states that at maximum apertures of f/6.7 to
f/8, the center CT sensor is sensitive to horizontal lines only, and "the other
focusing points cannot be used for AF." We know that vertical-line sensitivity
for the center CT sensor is not supposed to extend below a max aperture of f/4
(did my test show it working at f/5.6? I really don't remember.) It would appear
from the manual, and from my test, that the other 44 sensors remain sensitive to
horizontal lines down to a max aperture of f/6.7.
> My EOS 1000FN, whose single autofocus sensor is sensitive only to
> vertical lines, behaves in a similar indecisive fashion when forced to
> work with horizontal-only detail (e.g. when I tried to focus on the eyes
> when shooting a portrait :-(
That seems odd. First, that it is sensitive to vertical rather than horizontal
lines. My little experiment showed me how difficult it is to find subjects with
strictly vertical lines compared to ones with horizontal lines (or a horizontal
component). I wonder if that design decision wasn't a carry-over from the
vertical-line split-image focusing aid in some MF cameras? It also seems odd
that it would have trouble with eyes, which are neither horizontal nor vertical.
FWIW, I've had little trouble autofocusing on eyes (bird's eyes, admittedly)
using the 2x extender on a 300/2.8L, although I will say that on the most recent
occasion I switched to MF to be sure I got the precise focus I wanted (and got
several frames where the focus was off!). Perhaps it's time for an EOS 30. . .
. ;-)
Craig ("It's fun to spend other people's money") Callahan
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