Johnny Johnson wrote:
> Before buying one you might want to try the same process using your
> current lens. I've found that, in my case, using the in-focus
> indicator is hit and miss - kinda like my manual focusing using the
> focusing screen.
>
I tried that when dong macro lens tests. Using the 90mm macro lens in MF
mode, the in-focus indication wasn't quite as precise as manual focus.
That is, it tended to continue to indicate correct focus very, very
slightly on each side of the sharpest manual focus.
That's actually pretty good. I was working on a copy stand with good
light, a high contrast subject and using my eagle right eye, which has
20/10 acuity, about as good a setup as it can get for manual focus. I'm
pretty sure you would never see any difference between manual focus and
setting focus using the in-focus indicator except maybe wide open pixel
peeping. So I would tend to trust the in-focus indicator with that lens
in circumstances where I can't readily manual focus. This is an f2.8
lens, so the following discussion applies.
One thing that affects this is the speed of the lens. The 5D manual says
on pg. 78 that it will "execute high-precision AF with lenses whose
maximum aperture is f2.8 or larger." It goes on to say something sort of
unclear about how the center AF sensor has a different, higher precision
mode with faster lenses. So the results with the in-focus sensor may be
more accurate with f2.8 and faster lenses.
The only AF lens I have that is that fast is the little 50/1.8. But most
OM mount lenses that I would use with the in-focus sensor are either
super wide or f2.8 or faster. According to the 'Bay listing, the little
adapter reports f1.4 to the camera body, which should activate the high
precision focus mode.
A lot of blather to say that trying the in-focus indicator with AF
lenses slower than f2.8 in Manual mode may not be an accurate indicator
of how it would work with faster lenses. Of course, Chuck's lens is
f2.8, so a test with it might well be meaningful for use with fast OM
mount lenses with the chip adapter. Or not, there are so many uncertain
variables.
Moose
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