OK, I think I understand your point of concern. One of the reasons why
I selected such a long distance is because it negates a lot of the
focus accuracy issues which would dramatically change the outcome of
near-infinity objects. I repeated the test again over lunch. Just
walked back into the office a few minutes ago. This time I focused on
an object just over a meter away that had foreground and background
objects. In my initial inspection, the characteristics are repeated.
Tell you what. Why don't you define the exact test that you want me to
perform and I'll do it. Obviously, my own testing methods--as real
world as I attempt to make them, don't past muster. I would ask,
however, that you try the exact same test with your equipment too to
confirm the validity and repeatability of the test WITH multiple
lenses of your own.
In fact, if the test you devise is generic enough, other list-members
can perform the same test on their own equipment. I will gladly host
the results on www.zone-10.com for everybody to see. Maybe we need to
use tape-measures or something to provide and confirm precise focus
distances.
Chuck, let's go one step further. Please come up with the exact CoC
values to use and generate the hyperfocal distance and apertures to
use. Let's do it for FourThirds, APS and 35mm. This way we can also
compare real-world images for usable DoF vs Aperture vs Format.
However we plan the test and determine focus points, we do need to be
realistic. If I can't get an accurate and repeatable focus with a
tripod-mounted camera and live-view at maximum magnification I don't
know how to do it any better. I also did a maximum zoom on the
playback image to confirm focus accuracy.
It is possible that I'm making mistakes in my testing procedures. But
since they are also based on how I use the cameras in real-life with
real-life subjects I'd say that the results are accurate as they
perfectly reflect real-world usage, not theoretical calculations.
Again, this test confirms what I've been seeing with the lenses used
in real-life.
In the article on zone-10, the sample photograph scene is extremely
busy with tons of texture to gauge DoF on. I worked particularly hard
making sure I was focused on exactly the same point. The tripod never
moved and I used 2-second prefire. I did have to reaim the camera
slightly with the second lens because of variations in lens centers
and the IS. (I turned IS off, but the optics don't necessarily return
to exact center). When examining the original files, the image-center
is in focus and the foreground and background blurring occur at the
same places--but only at different rates. I chose to crop up slightly
from center because the OM-Z lens does have a curved plane of focus
whereas the Leica is very flat-fielded. By limiting the offset for the
crop, we stick pretty close to the center of the lens.
Today's test was different--using bronze statues in place of real
people, but shot from a common in-your-face people-event-photography
distance.
AG
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