![]() ![]() IIRC, they relied on high intensity UV light for exposure and had little visible sensitivity, but my memory may be faulty on this. ![]() They were also used by geological surveys and etc., as the papers were more reliable than the inked recorders. These products came in long rolls 5" and 10" wide for a variety of "instant" processing machines and were used in huge quantity by Cape Canaveral to record instruments during launch. They were by no means 20,000 true speed due to gaining some of their speed via reflectance from the paper support. Kodak made the Ektaline 2000 series papers which were similarly very fast and for the same reasons I described above. This is a paper based oscillographic recording material. What has been striking about film development since then is that the grain and sharpness of fast films have become so much better - T-Max 400 and Delta 400 can be used as standard films, particularly in MF and bigger, whereas Ilford HP3 was extremely grainy in 35 mm (but great in 4x5" and 8x10"!). It remained in production until around 1970. The benchmark fast film in England was Ilford HP3, which came out during World War II and was effectively ISO 400. EJ Wall and FJ Mortimer, undated but published I believe before World War I), there is an article testing 4 types of plates using H&D methods which states speeds as 80 - 150 H&D, 150 - 250 H&D, 250 - 325 H&D and 325 - 400 H&D respectively, the groups being more or less high-contrast copy material, slow general material, fast general material, and ultra-fast material giving less image quality and only really useful in extreme situations.Īs others have said, different speed systems are based on different methodology and are therefore not directly comparable, but as a ROUGH guide, H&D speed divided by 40 gives some indication of modern ISO speed. However, in a copy of the "Dictionary of Photography" (ed. For a few years after this, plate and film manufacturers avoided publishing speed numbers since the H&D system was open to abuse and allowed absurdly high numbers to be claimed. If you regard dry plates (invented 1871, well established by 1879/80) as the first commercially available film, you will not find any speed numbers in literature for these, since sensitometry as a precise science was pioneered by Hurter and Driffield, who published their first work in 1890. In a 1954 issue of "Leica Fotografie", a writer suggested that the DIN system be revised " in a manner that will have regard to the type of development that is normal to everyday practice". That wouldn't make the speed index too accurate if the developer in question wasn't available or used. For instance, DIN was at a time based on exposures which gave an 'optimal' density aim point with prolonged development in a GIVEN type of developer. ![]() The different systems in use determined emulsion speed various ways. The DIN system wasn't always that accurate. The safety factor was removed by the 1960s so that original 80 ASA became 160 ASA- the "improved" Plus-X of the time sped up to 160 from its original 80, but eventually became officially 125. ![]() This 80 ASA contained a 'safety' factor which allowed for discrepancies in the real film speed, as well as meter and shutter/aperture differences. Eventually the makers of both films and meters came together and devised standard indeces like the ASA, which came about in the 1940s. So they devised their own: GE and Weston assigned their own values to films (with some cooperation with the makers - for instance "fast" Dupont Superior-3 from the 1930s had a speed of Weston 64, and GE 56). When the photo-electric exposure meters started coming, there was no standard index yet. But when 250 H&D is converted to ISO, it would only be between 8-6. In a modern, ISO-driven context, the 250 rating would sound fast. ISO equivalents (or 'translations') for older values -those which antedate the ASA systems- NOT the reassignment of ASA into ISO.įor example, a 1920s NC film would perhaps have a given speed of 250 H&D. ![]()
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