[Leica] re: how easy/expensive is digital

["Tom Lianza" <tlianza@sequelimaging.com>]

Hey Austin,

Sorry, I can't resist:
You wrote:
    It's a tough job educating the world, but hey, someone has to do it ;-)

I know it was said in jest, BUT ....

You are quite right, educating the world is a tough job, and based upon your
some of your responses to this group, it doubtful that you, alone, are up to
the job.

You wrote:
/***************************************************************/
I've been designing this stuff for over 25 years, and I've never heard of a
"dedicated digital lense".  There are lenses that are designed to match the
MTF to the sensor pitch, but whether that really improves things or not has
yet to be demonstrated...  I've tested both high end lenses, and supposed
"digital" lenses...and have not seen any advantage, with the same
sensor...and be aware, that the specific lense has to be matched to the
sensor, which means that it's only good for THAT sensor, not for one with a
higher pitch or lower pitch...
/***********************************************************/
While it is true that Rodenstock and Schneider have really spun some
marketing nonsense in this area, let's not confuse the marketing hype with
reality.  There ARE lenses that are designed specifically for use with
digital sensors.  The MTF matching issues that you speak of are not really
the issue, the location of the exit pupil is usually the issue.  The
designer has to have a sense of the sensor geometry and any other "add ons",
microlensing, etc.  The aberrations are balanced based upon a different set
of criteria.  This is particularly true with issues of coma.  Digital lenses
will generally depart from the symmetrical forms found in photographic
imaging.  One of the two companies mentioned above, generated a white paper
a few year ago that was obviously not peer reviewed prior to publication.
That's where the urban myth of "sensor balanced MTF" came from.  The white
paper advocated using the lens as a low pass filter to limit the aliasing
introduced by the sensor.  There were two flaws in that general thinking:

A. It's real hard to make a lens that has relatively low resolution and high
MTF at the lower frequencies (without putting structure in the stop).

B. Many of the off axis color issues are based on the angle of the chief
ray, and balancing a lens design without correcting that point, yields a
lens that works well on axis and not too well off axis.  The standard off
axis color correction techniques don't work because the abberation is
introduced by a sensor interaction.

You noted that you have tested lenses of various types and you did not see a
difference.  Without any background about the test, the test metric, and
test equipment, doesn't that represent the same type of blanket, self
serving statement that you so often accuse others of using?

You wrote:
/*****************************************/
  You can adjust the color fidelity of film same
as you can digital, so I don't see how that claim holds.
/************************************************/
The first part of your sentence, prior to the comma, is sophistry.  The part
of the sentence following that comma is true.  Roy Berns ( an educator) , at
R.I.T. has written a rather good paper on this subject in the context of
archival capture of color in the museum.

http://www.cis.rit.edu/people/faculty/berns/research-mvsi.html

 Film has three characteristics that define and limit the gamut of the
reproduced color: the basic sensitivity of the color layers, the
interstitial color filters, and the dyes used in the production of the final
color.  The latter represents the fundamental limitation of gamut and the
two other issues result in colorimetric error. Film is a two step, chemical,
color reproduction process that limits the range of input colors to the
extent of the gamut reproducable by the dyes used in the formation of the
image.

Digital scanning products with visual color matching function response, have
been delivered to the packaging and graphic arts markets for well over 20
years. These products offer excellent color reproduction and require far
less processing to match original colors in print applications.  Most
importantly, the provide useful color information out side of the
reproducable range of film and they allow specific areas of color space to
match up better with printable gamuts so there is a lot less correction that
needs to be done.

If you look at the Kodak site and download some of their sensor literature

http://www.kodak.com/US/plugins/acrobat/en/digital/ccd/kaf16802ce.pdf

you will see that the RGB sensitivity functions overlap quite a bit.  These
sensors can capture the full spectral range of the human visual system with
out gaps.  The reproduced colors may be off, but they are still captured.
The above link is for a camera sensor.  The link below is for a sensor
traditionally used in line scanning applications.

http://www.kodak.com/US/plugins/acrobat/en/digital/ccd/kli14403.pdf

The sensitivities for this sensor have less overlap and the peaks are in
different places.  These sensors have been designed for other applications
in scanning such as negative emulsion scanning or paper products.  Kodak and
other sensor manufacturers offer a rather broad range of application
specific sensitivities that make the job of getting accurate color  easier
and often much better than film.  Companies are employing these sensors and
developing techniques for arriving at color reproduction levels that simply
are not addressable by chemical means.

One of the greatest educators I ever met was a man named Hollis Todd.  He,
and Richard Zakia wrote a book called Photographic Sensitometry: the Study
of Tone Reproduction.  Many years ago, as a graduate student and teaching
assistant, I was given the honor of talking at his retirement.  I recounted
that I never really thought that Hollis was much of a teacher.  I waited for
the collective gasp and inevitable buzz and then went on to explain why THAT
made him such a great educator: there wasn't a day that went by that Hollis
hadn't learned something new,often from his students,  and there wasn't a
week that went by that we (his class and himself) didn't discover something
new together.  Hollis didn't share his knowledge, Hollis shared himself.
Hollis encouraged skepticism.  The goal was never to prove a point, only to
learn what was right.

The imaging world is filled with a lot of marketing hype.  It's a said
reality.  As imagists, we need to share our experiences and each of us must
try to relate those experiences to our own context.  As a result of some of
my work in color science, I often get students or practioners writing to me
for advice.  I usually take the "Hollis" approach, point them generally
north, share some knowledge about the topic, and correct a specific errors.

I read this forum because I get a kick at viewing the images, listening to
the sometimes absurd political and technical arguments, and learning more
about a true love of mine: Leica cameras and imaging. I occasionally post to
this group to share an experience or some knowlege that I've picked up over
the years. I don't give a big rat's ass about educating the world, I'll
leave that to you, but for goodness sakes, hold yourself to the same
standards that you hold other contributers to this list.

Tom Lianza
Technical Director
Sequel Imaging Inc.
25 Nashua Rd.
Londonderry, NH 03053

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