[rollei_list] Re: Slightly OT: Why no advances in film?
- From: Emmanuel BIGLER <bigler@xxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sun, 15 Jan 2017 09:52:40 +0100
From Jeffrey L. Bromberger:
.... we're here now in the mid of the 2010s, and "science"
can't bring us anything more light sensitive than ISO 400, at best?
.....
For that matter, is there no silver-based methodology that's more sensitive
than 3200?
Hello from France!
First, it should be reminded that Polaroid Corp. had on catalogue a
silver halide product rated ISO 10,000.
This Polaroid (film+paper) combination was intended to record
oscilloscope frames in the one-shot mode, in the good old days of
cathode-ray tubes and 100% analogue electronics. Later, ISO 3000
Polaroid B&W film was a standard product and was discontinued ...
well, when all Polaroid silver halide products were discontinued.
Nowadays, even if oscilloscopes have kept their ergonomy: one button
or one knob = one function, they are nothing else than computers with
a signal digitization system.
Hence, what you see on the screen of a modern oscilloscope is just a
plot of some digital data that can be exported under a variety of file
formats, there is no longer any need for a one-shot analogue photo
of the screen.
Are digital sensors that much better than silver for capturing
photons of light?
Yes, definitely, and I'll elaborate shortly below.
Maybe it's time that we come up with a "different" film,
one that isn't digital, but uses something more light sensitive than the
current chemistry provides. What could we even experiment with?
At the end of the last century, French scientists, in cooperation with
AGFA, patented some new principles for increasing film sensitivity.
The principles were derived from some already known techniques in
astronomy, named hyper-sensitization.
https://en.wikipedia.org/wiki/Photographic_hypersensitization
I do not remember the exact scientific details of the research and
related patents of the French team, but those advances came too late,
at the end of the nineties.
In France, 2002 is the year when sales curves for film and digital
cameras crossed, up for digital and down for film, and I do not want
to remember the subsequent events, bankruptcy of AGFA Leverkusen,
Kodak under Chapter 11, etc...
You'll find here an official press release by CNRS (Centre National de
la Recherche Scientifique, one the the most important French public
research institution), dated Dec. 23, 1999 (better late for the XX-st
century than never ;-) ), related to this research.
The text is in French, but you'll probably find a translation somewhere.
http://www.cnrs.fr/cw/fr/pres/compress/emulsionsphoto.html
The research, conducted by a scientific team leaded by Jacqueline
Belloni, had started in the mid nineties, but since many importants
aspects of the research could be patentable and applied to the
industry, nothing was publicly released before the patents were issued.
Here is one patent
http://www.google.com.na/patents/EP0922994A2?cl=en&hl=fr
European patent EP 0922994 A2 issued June 16, 1999
"A photosensitive silver halide element with increased photosensitivity"
Inventeurs Jaqueline Belloni-Cofler, Keyzer René De, Remita Hynd, Mona
Treguer
Déposant AGFA-GEVAERT naamloze vennootschap
Remember that patents are enforced only during 20 years, hence this
patent will be in the public domain as of June, 2019 (in 2019 we'll
celebrate the 99th anniversary of the Rollei company!)
--------
Now regarding a comparison between film and silicon as image
detectors, even if we do not take into account the benefits of the
immediate availability of a data file, the possibility of white
balance in a variety of colour temperature by a simple software
setting, etc.. the reasons why silicon is much better than film is
certainly not in the number of possible pixels in the image (just
think of a 8"x10" 'chrome digitized on a drum scanner), but in the
efficiency of photon detection.
One of the most difficult part of film theory, modelling and
characterization is determining an equivalent quantum efficiency of a
silver-halide layer.
This has been done, and you can find in a legendary book by Pierre
Glafkidès (he was a research engineer at Kodak in France) some figures
related to the equivalent quantum efficiency of film.
Chimie et physique photographiques by Pierre Glafkidès
P. Montel, 1976 - 1033 pages (this is the last edition)
https://books.google.fr/books/about/Chimie_et_physique_photographiques.html?hl=fr&id=ZuE0AAAACAAJ
an English version exists but seems hard to find
Glafkides, Pierre, Photographic Chemistry, 2 volumes, Fountain, London 1958.
Well, to put it short, a beloved film like Kodak TRI-X, according to
Pierre Glafkidès, is only credited of an equivalent quantum efficiency
of 0.4%.
In other words, film wastes more than 99% of incidents photons in
terms of detection efficiency!
As a comparison, a photocathode used in a photo-multiplier tube has a
quantum efficiency of 40%
And a consumer-grade digital camera can be credited of a minimum of
30%, and silicon photo-detectors using the so-called back-lighting
technology can exceed 80%
The consequence is that for a given noise figure in the final image, a
consumer digital camera needs about 100 times less photons per pixel
than Tri-X film!
This advantage of silicon image sensors for the consumer market was
not immediately visible by the end user as long as the number of
pixels was, say, below 2 millions. Digital image quality was poor at
the beginning, I painfully remember at the end of the last century one
colleague proudly showing me the poor images he had done with a 500-K
pixel camera! Well, this colleague had never seen a 20"x20" print made
from a Rolleiflex TLR... ;-)
Call this a micro-rant. I'd love to be able to shoot chromes indoors, in
low light, without having to sit dead still for seconds at a time. Now, it
seems as if indoor slides are dead, especially since the new lighting (LED,
CF and the like) are so different from tungsten (and each other), making
color correction more unlikely than ever.
Yes, to date, there is no longer any colour slide film balanced for
tungsten light available.
The problem is just economical, profitability, the market for this
kind of product is too restricted.
So: wait and see, if Kodak can bring back Ektachrome film in 120
rolls, we'll be happy, but first, even if it has been recently
announced, it is just an annoucement, and only 135 ektachrome is
announced.
All the best
--
Emmanuel
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