I just tried the Tokina 28-80/2.8 of the 5D in manual mode and the focus
confirmation indicator is extremely sensitive. I don't seem to be able
to hold the camera with this heavy lens, half depress the shutter button
and turn the focusing collar to within some fraction of a millimeter to
hold the light steady on instead of blinking and beeping. Looks like it
will take some practice on technique. Getting old and shakey I guess.
On another note, I downloaded the focusing accuracy chart from here
<http://www.focustestchart.com/chart.html> and discovered that the lens
is decidedly front focusing. At least when up close as illustrated in
the test procedure. Seems totally at odds with my earlier tests where I
discovered that the camera/lens were focusing much more accurately than
I could do manually with OM mount lenses on the camera. In this test
scenario I seem to be able to manually focus (with the Tokina) much more
accurately than the camera.
Right now I'm totally befuddled as it doesn't seem to make any sense.
However, in my earlier tests of photographing a map I was about 4 or 5
feet away instead of about 2 feet with this small (8-1/2x11) test chart.
Maybe some peculiarity of the Canon's center sensor. The test chart
was produced for a Nikon D70 and has only a horizontal black bar with
some teeny text inside. But, as far as I know, the center sensor in the
Canons and Nikons is sensitive to both horizontal and vertical lines.
Looks like lots more testing is in order. I don't understand it.
Chuck Norcutt
Moose wrote:
> 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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