Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site peora.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!mtuxo!mtunh!mtung!mtunf!ariel!vax135!petsd!peora!jer From: jer@peora.UUCP (J. Eric Roskos) Newsgroups: net.rec.photo Subject: Re: film sharpness Message-ID: <1166@peora.UUCP> Date: Tue, 25-Jun-85 15:26:34 EDT Article-I.D.: peora.1166 Posted: Tue Jun 25 15:26:34 1985 Date-Received: Thu, 27-Jun-85 05:21:17 EDT References: <2807@decwrl.UUCP> Organization: Perkin-Elmer SDC, Orlando, Fl. Lines: 86 Um, while I will agree with a lot of what you said [I posted the original article you are commenting on], a few of the statements aren't entirely accurate (though close):* > 1. Reversal films such as Ektachrome are inherently finer grained > than the equivalent negative film, because in the negative film > the image is made up of the larger grains of silver which pick > up light better. In a reversal film, the image is made up of what's > left after the large grains are removed in the reversal process, i.e. > the smaller grains. Kodachrome film does not use silver, I don't think. However, I believe other reversal films do. This is one reason why Kodachrome has better grain/sharpness. But, negative film does not leave behind the silver grains either. The silver grains produce "dye clouds" during development; but during the last step of the development process (the "Blix" step in 2- step processes), the silver grains are chelated out with EDTA, leaving only the dye behind. The main reason why negative film has a POTENTIAL for greater graininess is that negative-working paper has higher contrast, and consequently can make the graininess be exaggerated. The reason it has higher contrast is that print film has lower contrast than reversal film. The reason for THAT is that print film has a greater "exposure latitude" -- a wider range of luminance produces different densities in the film than in reversal film, because reversal film has the constraint that the densities produced in the film are those used to actually view the image. Along with the wider range of exposure latitudes comes a smaller relative difference in densities between two luminances (in the linear portion of the characteristic curve), since there is only a certain density range that is usable, for practical purposes. This is a design decision in the manufacture of negative film. Just as B&W negative film doesn't give the same densities in the negative (e.g., there is a visibly-grey base+fog density, Dmin) that appear in the print, so you can adjust the appearance of your print by varying the exposure of the paper, so also color negatives do likewise. > 2. But market conditions are that most pictures are made with > color negative film, therefore they put more effort into the negative > films. An example is the new range of high performance print films. Actually, it's not "market conditions". I wrote a letter to Kodak about this a long time ago, asking "given the fact that you make negative film specifically for making prints, why is it that people claim the quality of reversal film (for prints) is so much better? Why don't you optimize the negative film for making prints, and the reversal film for making slides?" Kodak wrote back (just recently) and said, in essence, "we do. It's just that some people prefer high-contrast prints and saturated colors. We make the negative film to suit what are considered normal print properties by professionals in the industry. It's just a matter of what the individual prefers." > 3. Kodachrome has an advantage over Ektachrome because the emulsion > is thinner. This is because the dye is added in during processing in > the Kodachrome method. This is true. Despite my dogmatic Realism-based opposition to people's obsession with Kodachrome, actually it is very good film, for slides. However, print film has another interesting advantage that is not related to emulsion thickness -- most of the print films have 2 emulsions in each color, one faster (but coarser) than the other. This is why many people overexpose VPS film (which is rated at ASA 160) by exposing it at ASA 100; it exposes the finer emulsion more, and gives a finer grain. You can do this with print film because of the above exposure latitude. > But back to reality, aren't the full-page spreads in Time, Sports > Illustrated, etc, good enough? They're mostly taken with 35mm film, hand- > held... Well, except that they are usually printed through a halftone-screen, which introduces a severe "grain" of its own! ... actually Audobon Magazine experimented with printing without halftone screening about 8 years ago. This produced very beautiful prints, although many of them had flaws where the dye didn't go on uniformly. But I haven't seen many magazines that do that (and I really don't know how Audobon did it, either). --------- *Of course, venerable and more experienced photographers in here may well find errors in my statements, too! -- Shyy-Anzr: J. Eric Roskos UUCP: ..!{decvax,ucbvax,ihnp4}!vax135!petsd!peora!jer US Mail: MS 795; Perkin-Elmer SDC; 2486 Sand Lake Road, Orlando, FL 32809-7642 "Erny vfgf qba'g hfr Xbqnpuebzr."