I really don't have any desire to spec such a test since I'm not sure I
could and I don't really care if you're correct or not. My only point
was that... you haven't proven your point... at least with that test case.
Chuck Norcutt
Ken Norton wrote:
> 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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