On 11/21/2011 6:41 AM, Chuck Norcutt wrote:
> Still much difference in brightness and very difficult to compare.
What are you trying to compare? Although not what I was looking for when I took
these test shots, a clear result IS the
differences in 'exposure' or 'brightness'
I was looking first for differences in bokeh. I am not happy with the bokeh of
many modern lenses, and was curious about
an older, non-symmetrical design with fewer elements. Second, I was also hoping
to find differences in that elusive
quality sometimes discussed here and elsewhere, 'drawing', 'rendering' and
similar fuzzy terms. Third, I was interested
in any obvious difference in sharpness.
Those weren't what I found. Bokeh, at least at these apertures and
subject/background distances, isn't much different.
"Rendering"? I can certainly see the difference between the soft, but somehow
sharp rendition of good LF portrait lenses
and the edgy sharpness of small format lenses. But I saw no real difference in
that area here.
Sharpness? Although I mis-focused a bit, so that the Tessar didn't have the
same focal plane as the others, with the
limited parameters of this test, I don't see any significant differences. With
the 60D and FF coverage lenses, I'm also
not looking at the whole output of the lens. It would take quite a different
test target and set-up to really test that.
It's also useful to remember that 'sharpness' isn't a measurable thing. It's a
poorly defined combination of resolution
and edge contrast. With contemporary PP tools, modest edge definition and edge
contrast failings in a lens are
relatively easy to correct.
What I did find was interesting and complex differences in luminance
distribution and in color. In my initial
processing, I was careful to distort the lens response as little as possible
while compensating for differences in
mechanical aperture accuracy, which is secondary to optical qualities.
So I used Exposure in ACR to put the top of the recorded image data just at the
top of the histogram, 'kissing the
post', and set Blacks to zero, with no other adjustments like Recovery, Fill
Light, etc. to distort the histogram.
That approach "failed", in that the central tones were in different positions
relative to the ends of the histograms.
But it was a success in that it showed that these very different lenses
actually distribute the light that travels
through them differently. Exposure to place midtones in the center would work
well with one and result in blown
highlights with another.
Then I went a step further. I used the Filter=>Blur=>Average tool to measure
the average brightness of each image and
adjusted the midpoints of the histograms in Levels to make them all the same
average brightness. I can't think of a more
accurate measure of equal brightness than that.
And still you see "much difference in brightness". And yes, they do appear
different, but I submit that the difference
is in the distribution of luminance and color, not overall brightness. Move
between them looking at different details.
What I see is differences in the relationships of nearby brightness and color
in areas much smaller than the whole image.
My conclusion so far is that there is more difference in these details between
lenses than I would ever have imagined.
Perhaps I shouldn't be surprised. They are very, very different lenses, a four
element design from early in the history
of lens design with single coating, a multi-coated, six element, relatively
modern version of the old double-Gauss
formula and a recent 11x zoom with 15 elements, including two kinds of exotic
glass, aspheric surfaces and much more
highly developed multi-coatings.
> Maybe it's a hopeless task. Pick the one you like.
Not hopeless; the differences you see ARE the differences in the lenses, not
some failure of exposure. And indeed, it's
"Pick the one you like." That's the point of such a test, isn't it?
I like the Tessar best, at least for this kind of subject. But I am happy that
the Tamron is very close, perhaps even
more accurate, and that's what I use day to day.
Testy Moose
--
What if the Hokey Pokey *IS* what it's all about?
--
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