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Kodachrome vs. Velvia

Federico Agostini , Sep 12, 1999; 07:03 a.m.

On an interesting article by Erwin Puts about Leica lenses there's a paragraph concerning the "superiority" of Kodachrome vs. Velvia. He states, knowledgeably, that K "is grain based where V is dye cloud based". And that "a grain image is an exact replica of the optical image falling onto the emulsion" whereas "the dye cloud image is a chemical interpretation of this image". My question is: does the dye cloud process apply to all the E-6 emulsions or particularly to Velvia? Thank you for answers and comments.

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Ellis Vener , Sep 12, 1999; 11:45 a.m.

It applies to all E-6 & C-41 films. Think of dye clouds as "shadows" left by the original photochemical lightreceptors. They are different technologies, one not necessarily superior to the other.

Patrick Giagnocavo , Sep 12, 1999; 05:05 p.m.

Kodachrome is different from other color slide and print films, in that there is NO color in the original film!

Instead, there are three layers of black and white film, each sensitized to different parts of the visible light spectrum.

During processing, the color is added, and somehow couples to the right layer.

Neal Vaughan , Sep 12, 1999; 05:39 p.m.

Can anyone else confirm what patrick just said?

Stan Benkey , Sep 12, 1999; 05:41 p.m.

Yes ... Kodak can confirm it.

grant groberg , Sep 12, 1999; 10:27 p.m.

any URLs to reference us to?

Ellis Vener , Sep 12, 1999; 10:57 p.m.

As a non-Kodak employee I can confirm it, I watched Kodachrome be processed at the old New York Filmworks lab in the early or mid 1980s. The color dyes are added during the processing. As to whether "the a grain image is an exact replica of the optical image falling onto the emulsion..."' is a true statement. I can't confirm that. My impression, speaking from a philosophical crag overlooking a vast technical valley in my knowlege, is that all images, whether recorded on film or digital media, are analogs (i.e., representations ofthe real event) of the actual event. (Before you criticize my use of the word "analogs" in this context, I suggest you look the word up in a dictionary.)

Dan Sapper , Sep 13, 1999; 02:36 a.m.

Both K-14 and E-6 films are dye-cloud images. Color imaging dyes are formed for cyan, magenta, and yellow. When combined, they provide the infinite variety of transparent color you see.

Kodachrome is unique in that the color couplers are in the color developing processing solutions. Ektachromes (and other manufacturers' chromes) have the couplers coated into the corresponding films layers; cyan in red sensitive layer, magenta in green sensitive layer, and yellow in blue sensitive layer.

Kodachrome process is a wonder to behold. There are four developers and two re-exposures to light.

K-14 First Developer brings up the negative black and white image in the silver (E-6 also has a B&W first developer).

After K-14 first developer, the film is next exposed during processing to pure red light, through the base-side of the film, closest to the bottom red-sensitive emulsion layer. This exposes the remaining undeveloped red-light-sensitive silver halide to provide a reverse (positive) image.

The next developer is the Cyan developer. In K14, each color developer has a unique developing agent which only couples with the freshly "re-exposed" layer. hence, you get a "positive" dye-cloud image in the proper layer when processed in the proper sequence.

Third, the film is re- exposed in-process to pure blue light, through the emulsion-side of the film, closest to the top blue-sensitive layer. This reverses the blue-sensitive silver halide. The next developer is Yellow, which works like the cyan described above, but with a different developing agent, and of course Yellow dye-coupler.

Fourth, the film goes directly into the Magenta developer. It is not re-exposed to green light. Instead, there is a chemical fogging agent which "fogs" any undeveloped silver halide in the film. By this point, the only silver halide is in the green sensitive layer, because all the other layers have had both negative silver developed, and the reversed silver-halide developed into dye clouds. So the green-sensitive layer is chemically reversed, and the Magenta coupler-containing developer goes to work on whatever silver halide remains.

Then the rest of theK-14 process is like modern color film "tail" solutions. Bleach the developed silver back to the silver-halide state. Fix the silver-halide into solution out of the film. And an assortment of washes in between. Fourteen steps in K-14 leave you with a dye-cloud image.

E-6 has a First Developer and only one Color Developer which develops the couplers coated into the specific layer structure of the film.

I get a thrill just thinking about the complexity of K-14. When it is done properly, the results are truly stunning!

Mark Ci , Sep 13, 1999; 02:09 p.m.

It sounds like Erwin ain't so "knowledgeable" after all.

Mike Scarpitti , Mar 15, 2000; 08:44 p.m.

The dyes in Kodachrome are crystaline, rather than organic (E-6), and are MUCH smaller particles. E-6 dyes is like a big fluffy cloud that is close to the grain, whereas the Kodachrome is like a sharp nail that sticks right through it. Irwin is right, but perhaps he didn't explain it as well as could be.


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