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film speed for old films
Sorry, but I have lost the original thread. I was posting about film speed
of pre-WWII films to compare with modern film in a Kodak Brownie camera. It just so happens that Popular Science has made their archives publicly availaible and I looked up the December 1941 isssue as that was the last one before the US entered the war. The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80 tungsten) for night shots. In comparison, Kodacolor was ASA 20. I'm not sure about Kodachrome it was either ASA 8 or 10. Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or understanding, as in he has a sub-wikipedia understanding of the situation. i.e possessing less facts or information than can be found in the Wikipedia. |
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film speed for old films
On 10-03-04 18:24 , Geoffrey S. Mendelson wrote:
Sorry, but I have lost the original thread. I was posting about film speed of pre-WWII films to compare with modern film in a Kodak Brownie camera. It just so happens that Popular Science has made their archives publicly availaible and I looked up the December 1941 isssue as that was the last one before the US entered the war. The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80 tungsten) for night shots. In comparison, Kodacolor was ASA 20. I'm not sure about Kodachrome it was either ASA 8 or 10. We've come a long way. I remember shooting a lot of Kodachrome in the early 80's and thinking 25 was a fine speed of film... Since I shoot a lot from a tripod, it still is, I suppose. -- gmail originated posts are filtered due to spam. |
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film speed for old films
Geoffrey S. Mendelson wrote:
Sorry, but I have lost the original thread. I was posting about film speed of pre-WWII films to compare with modern film in a Kodak Brownie camera. It just so happens that Popular Science has made their archives publicly availaible and I looked up the December 1941 isssue as that was the last one before the US entered the war. The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80 tungsten) for night shots. In comparison, Kodacolor was ASA 20. I'm not sure about Kodachrome it was either ASA 8 or 10. I have some old tower catalogs and they pretty must say to only use print film in the box cameras due to their limited control. From my experience with the simple Tower and Ikon ones I have shot with, 50 ASA print film in daylight works pretty well (Ilford pan F) or I have put a deep yellow gel inside and shot with 100 speed B&W. The yellow filter helps the image quality quite a bit! I would guess if you wanted to "dial in" one of these for modern film in daylight you could play with ND filters till you got the exposure right? My old Ikon has 3 waterhouse stops which helps. You might be able to add one to a brownie, which would probably help image quality too. Stephanie |
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film speed for old films
"Geoffrey S. Mendelson" wrote in message ... Sorry, but I have lost the original thread. I was posting about film speed of pre-WWII films to compare with modern film in a Kodak Brownie camera. It just so happens that Popular Science has made their archives publicly availaible and I looked up the December 1941 isssue as that was the last one before the US entered the war. The Kodak ad in there was for Verichrome (not Verichrome Pan, which came in the 1950's) which was ASA 50. It also mentions Super XX (100 daylight, 80 tungsten) for night shots. In comparison, Kodacolor was ASA 20. I'm not sure about Kodachrome it was either ASA 8 or 10. Geoff. Beware that the original ASA sytem had a one stop safety factor. All those speeds doubled when the ASA dropped the original method and adopted a modification of the DIN method about 1958. The original ASA method was based on extensive research done at Kodak Research Labs by Loyd A. Jones and his associates. There intension was to find the _minimum_ exposure which would result in good tone rendition. The problem came when the ASA adopted this system as a standard. For some reason they decided to halve the speed determined by the test. Up to the adoption of the ASA system about 1943 Kodak published "Kodak Speeds" which were determined directly by the Jones method. These were four times the ASA speeds and exactly double current ISO speeds. The two to one change was made to adopt the speeds resulting from the test to existing meters which used mostly either the Weston or General Electric scales. The ASA speeds fell exactly in between these two so could be used on either kind of meter with minimal error. The main reason for changing the standard speed method from Jones' minimum usable gradient method to the DIN minimum density above fog and support density was the difficulty of making the Jones type measurement which requires finding the point on the toe where the gradient (contrast) is exactly one-third the gradient of the straight-line portion of the curve. The ASA found that the DIN method would result in just about the same speed point if a fixed factor of 1.25 was applied to the indicated speed point. The DIN method and the current ISO method is to expose and develop the film in a controlled way that results in a specified density range corresponding to a specified exposure range, i.e. essentially a fixed contrast index. The speed point is then the point is then where the density is log 0.1 above the gross fog and base density. A multiplier of 1.25 is applied to this to get the speed. This method applies _only_ to black and white silver-halide negative film intended for use in still cameras. A different standard exists for motion picture negative film and other standars for color films and for reversal films. The reason Jones wanted to find the minimum exposure was that, in general, film yields the finest grain and sharpest image for minimal densities. This is, of course, mainly a concern for small negatives. Jones found that he could get "excellent prints" when the minimum shadow exposure was on the toe where its gamma or gradient was one-third the overall contrast. Decreasing exposure rapidly degraded the image quality but increased exposure had little effect up to many stops over-exposure. Probably the ASA wanted to adopt a speed standard which would be reliable in terms of producing a usable image so took advantage of the overexposure capabilities of film. Of course, they lost the original intent of producing the finest grain and sharpest images. Color films were always measured by a different system. Reversal films especially must be accurately exposed because they use virtually the full range of densities possible and have very little latitude. I am of course writing about reversal for direct viewing. There are low contrast reversal films for duplicating purposes. The original Kodachrome had a speed of about ISO 8 to 12 depending on whether it was daylight or tungsten balanced. However films like Plus-X and Super-XX had speeds much like today, i.e., around EI 125 for Plus-X and 200 for Super-XX, exactly double what the published speeds of the time were. The biggest difference in these emulsions for the later ones was grain. Current Plus-X is substantially finer grain than the original version and is sharper. All of these old films used multi-coated, thick emulsions which had considerable light scattering (irradiance) which caused a loss of resoution and sharpness. In fact, the use of ultra-violet light was adopted for making motion picture sound negatives in the 1940s in order to confine the exposure to the surface of the emulsion and so increase resolution and reduce distortion. -- Richard Knoppow Los Angeles, CA, USA |
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