What's the point with ISO 125?

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Ehm... maybe I haven't understood the whole ISO metric system (100, 200, 1600, 6400, and so on...) very well, but... what's the deal with 125 films?!

I mean, there's an obvious difference between, say, 100 and 400 (grains, speed, and more), but what big a difference could there be between 100 and 125? It's not so much faster that you can clearly see a difference in the grains or so. So... what's the point? Am I missing something? I've tried using Kodak's 125 film, with not so positive results compared to Tmax 100 or Fuji's Neopan SS, so... does anyone know the "secret" behind 125 films?


-- Ulisse (d92-upe@nada.kth.se), September 10, 1997


You're referring to Plus-X, right? Plus-X and Tri-X (ASA 125 & 400) are very different to T-Max 100 and T-Max 400 (100 & 400, hardly suprprising).

In a similar vein, Ilford have FP4+, HP5+, Delta 100 and Delta 400.

The newer emulsions have a very different grain structure, among other differences. Some photographers prefer the new, some the old. So the point of Plus-X is not to provide and "extra" speed between 100 and 400, but is available as Kodak's "old" emulsion at (about) ASA 100.

Strictly speaking, it's called "ISO" rather than "ASA". The American Standards Organisation no longer exists. The International Standards Organisation does.

-- Alan Gibson (gibson.al@mail.dec.com), September 10, 1997.

The point is simply showing a bigger number! In the old days manufacturers thought they could gain a competitive advantage with "faster" films. Like General Motors, big companies make changes in attitude slowly, if at all. This is especially puzzling because the published ISO's (EI's) are never accurate! They are usually off by as much as one stop. True film speed is determined by measuring the point on the curve where density is 0.1 above film base + fog. By this method, the published ISO's are irrelevent. You should measure your own personal film speed, but if you don't have access to a transmission densitomiter, a safe bet is just to divide the published ISO by 2. See Ansel Adams' book "The Negative" or Fred Picker's VHS "Photograhic Technique" (avalilable from Calumet) on the proceedure for film speed and development time tests.

-- Michael D Fraser (mdfraser@earthlink.net), September 10, 1997.

The secret is simple. It is a film designed years ago and that is the speed Kodak came up with. Many photogs still use PlusX and love it. A number of pro labs output your digital B&W to PlusX for negs. If you work with it you can get excellent results, just as with every modern film on the market. If you have something you like better, for whatever reason, use that. The 125 speed films serve us by giving one more alternative to work with.

-- Dan Smith (shooter@brigham.net), September 11, 1997.

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