Ken Norton wrote:
> For the sake of argument (or non-argument), I'll agree with you,
> Chuck. We'll make the assumption (which may or may not be true) that I
> misfocused for the original test. Since I didn't have usaf charts in
> the scene, I was at the mercy of the details in the scene--which in
> this case is the grass. If I did misfocus, this does point out just
> how haphazard our focusing really is and we're just getting it close
> or maybe not-so-close most of the time. I did think my "real world"
> landscape shot with ultra-detail was a good indicator of lens
> performance, though.
I wouldn't worry too much about misfocusing. Afterall, the focusing
error in this case is easily within the DoF... although it doesn't take
a large error within that range to move and increase the DoF by a large
amount. CH said he thought you couldn't focus precisely within that 5-6
meter range because it is within the DoF. I wouldn't be that extreme
about it. I think it's probably true if you consider only DoF
resolutions typical of 8X enlargement but it is possible to achieve
resolutions better than that. We might be able to decipher that on a
10X liveview display but maybe we have to have targets at 5 and 7 meters
(or whatever) rather than 5 and 6 meters
>
> As to the 5D Mk2's live-view--it is my understanding that this camera
> doesn't use all pixels for live-view and skips pixels. This, again,
> would get you in the neighborhood but is anything, but exact. To
> differenciate a focus point at 5 vs. 6 meters with a "normal" focal
> length, the difference with most lenses is a whisper of a nudge. Like
> C.H. says, 0.5mm or so. The problem is that wide-open, there is
> usually just enough CA or other issues with the lens which prevents
> precise focusing to this level. As mentioned, stopping down the 24mm
> F2.8 lens to F4 acually make precise focusing more feasable. The
> line-pairs on the usaf lit up like a Christmas Tree when in focus. I
> could conclude, therefore, that it is possible the L1 has a superior
> live-view than the 5Dmk2.
I'd never heard this about the 5D Mk II live view and I'm not sure how
one would come to that conclusion. The display spec is 920,000 pixels
which I conclude means about 780x1170. The vertical dimension of a 5D
Mk II image is 3744 pixels. If we blow that up 10X then it gets divided
down to 374.4 pixels which doesn't have any trouble fitting into 780.
On the other hand, maybe 960,000 pixels means 920,000 RGB dots. In that
case the real display resolution is only 306,667 (real) pixels and the
resolution is only 260x390. In that case 374 vertical pixels doesn't
fit although I don't know how they could claim 10X.
>
As to the rest of your commentary I don't know except that I reject the
statement below. That is exactly what I don't believe you have
demonstrated despite the fact that you now seem to believe that it's
impossible to focus accurately enough to prove it.
> The emperical evidence shows that there is something
> beyond the simple algebraic calculations which assume simple optical
> traits.
Chuck Norcutt
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