I'm a Tri-X shooter for 35mm and 120 (for now), but I need some 4x5 stuff and I'm about to purchase my first box. I 'want to purchase a large box, so I'm looking at 25 sheet boxes. I'm also looking at 100-200 ISO films since I'm limited to 1/200th on my Speed Graphic's lens, and I don't trust the focal plane shutter right now, and I don't have any ND filters. Can anyone explain the difference between FP4 and Delta 100? One is ISO125 and the other is ISO100, and both of their descriptions sound very similar. Delta 100- Ilford Delta 100 Professional is simply the best in its class - offering the photographer exceptionally fine grain and a level of sharpness rarely seen, resulting in outstanding clarity of detail and the most precise image rendition. Capable of superb image quality at its recommended rating of ISO 100/21, this film will also produce great results rated between ISO 50 and 200. FP4- Ilford FP4 Plus is a very fine grain, outstanding sharpness and high acutance make it the film of choice whenever a job demands great enlargement or the subject contains a wealth of fine detail. Nominally rated at ISO 125, Ilford FP4 Plus has become the benchmark against which other medium speed films are judged. With enormous latitude for exposure error above and below its ISO 125, Ilford FP4 Plus is very suitable for most photographic subjects under a variety of lighting conditions.