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Re: (meteorobs) Comet film
Thankyou all for the informaton about the films you are using. I know a lot
about all of them as I used to work for Kodak. Tom your P1600 used to be
called P800-1600. It was a good emulsion when it came out as such. But
back then to use it at 1600 you had to push it. Now Mike keeps talking
about the grain of the film. In color film ther is no such thing as grain,
if you use the same definition for grain as used in black and white films.
In black and white films, the grain is an inherent property of the emulsion
itself. It does not matter how yo process it, the grain will not change as
lopng as weare talking about the same emulsion. Lets take Tri-X for an
example. The grain in Tri-X is the same whether you shoot it and process it
at 100 or at 400. It is a matter of the clumping of the silver . You can
magnify it and see the clumps. Now if you are talking about a T-Grain film
such as Delta 100 or T-Max 400, there is grain, but only because you are
still clumping the silver around the latent image. The difference is, the
shape of the silver crystals. The manufatures have figured out a way to
shape those crystals into the same basic shape all of the time, hence
tabular grain crystals or T-grain. Color film is completely different.
When you shoot the image, a latent image is formed just as with black and
white film. In fact, color film is like a muti layered black and white
film, with each layer sensitive to a different part of the electromagnetic
spectrum. Hence you can have some color films that are more sensitive in
the red and others in the green. But when you process color films, the
silver in the emulsion is removed before the latent image can be fixed, and
then where the image would have formed with silver crystals, various colored
dyes form the image. The dyes form a diffuse image with no crystalization
hence no grain. This is all found in the Kodak manuals on color developing,
be it the C-41 manual, the E-6 process manual (Z-119), or any of the manuals
that come with the home processing kits from other manufactures. Because
you have multi layers, the dyes respond differently in each layer. The dyes
can be denser in one layer than another, which when looked upon from outside
the emulsion, looks very much like grain. But it is not the same as the
grain as found in a black and white emulsion. In fact, nowhere in any color
data sheet from Kodak will you find mention of grain. Instead what you do
find is a term called granularity RMS. This is where the apparent diameter
of the dense areas are compared to the non-dense areas, and a figure is come
up with to express a rating for the film. The best ratings are 4-6. But if
you use some color films the rating can be as high as 10-20. The lower the
number (ie. 4 as compared to 10) the better the film. a lot of the Kodak
color films range from 4 to 15. With some of the T-Grain technology films
such as the old Ektar series, you could have the same amount of granularity
with Ektar 1000 that you did with Ektar 25. But there is a catch. The
granularity is effected by the chemical processing . That is one reason why
the temperatures used in color processing is higher, and more controlled
with less latitude then with black and white processing. Did you know that
you can use a color develope such as kodak's flexicolor developer to develop
Tri-x or any other old technology films. And you promptly have all kinds of
grain.
Many people who work at Kodak film labs have tried this experiment many a
time. I have. So please when you are referrring to color films do not use
the term grain in regards to the granularity found in the emulsion. Now, I
must again address the issue of color response. If a parent molecule in the
nucleus of a comet is released, it moves away from the nucleus. When it is
exposed to the radiation from the sun, it ionizes. Upon Ionization, it can
emit a spectral line. Each molecule has its own little set of spectral
lines that it can emit (basic spectroscopy and chemistry). If the spectral
line emited is in the blue part of the spectrum, you need a blue sensitive
emulsion to dectect it just as you need a blue sensitive CCD to detect it.
If you are using a red senisitive film, it will not detect any blue spectral
lines. That is one problem with using Tech Pan to try to image the tail
structure in comets. It can see or detect the red dust tail, but it can not
detect the blue ion tail. To detect the blue ion tail, you need a blue
sensitive film. Kodak used to make a bunch of them, but for the past
fifteen years the best readily available blue sensitive film was "Kodak
Commercial film" which was "..a medium speed, blue sensitive film with
moderatly high contrast....". The is a quote from the Kodak datat sheet
F-16. They stopped production of it in 2000. According to its spectral
sensitive curve, it was sensitive in only the blue and a portion of the
green. Hence it was called a blue sensitive film. Now Kodak's High Speed
Infrared film is sensitive in the infrared. However it is also sensitive to
light that is blueer the the infrared, that is why you use a red filter to
block out everything except the infrared. (ref. Kodak pub. F-13). That is
one of the major reasons to use filtration with some emulsions. But an
interesting thing about the High Speed Infrared film. If used with the
filter as recommended by Kodak (no. 25, 29, or 89B), it can not see the ion
tail of a comet. Again much of this is in the literature. Why don't you
guys read it.Today with CCD imaging, you have blue sensitive CCD's, red
sensitive CCD's, etc.. But I don't care what film or CCD you use. If it is
not the right film or CCD, it can not detect something if it is not
sensitive to that part of the spectrum. That means quite simply, if it can
not sense the radiation, no amount of prcoessing chemically or
electronically can insert that inofrmation so it is lost in and to that
image. So if you do not have that information, than there is no way that
anyone can create an image and say that that is how the comet looks, because
it is truly false...............................................
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