The H&D Curve

Wikipedia says “Ferdinand Hurter (1844–1898) and Vero Charles Driffield (1848–1915) were nineteenth-century photographic scientists who brought quantitative scientific practice to photography through the methods of sensitometry and densitometry.”

At  you can scroll down to the September 24 entry for an example of a Tri-X characteristic curve, as well as parodies of H&D curves (fo-do insider jokes). In each case the curve consists of a toe (shadow tonal separation), a straight line section whose angle indicates the inherent contrast, and the shoulder, which refers to highlight separation.

Ms. H. has this bone to pick:


‘For extra fine grain try T-Max 100 in either Microdol-X or Perceptol full strength. The grain rivals Technical Pan at about five times the speed and no problems with controlling contrast.’

“People were Microdol crazy when I was at school. Is this necessary? Why can’t people just invest in a tripod and use fine grain lowwwwww speed film? Straightforward and simple; slower film=better grain. Are my views skewed? I have always preferred most others over T-grain films- Is it just because my elders told me they were better? I look forward- perhaps this weekend- to enlarging some negatives to definitively answer such questions. Damn it.”


You’re right. A slower non-tabular grain film, exposed and processed in another standard developer, is probably preferable to fast T-Max or Delta. I suspect people find themselves in a corner once they’ve loaded a camera. Barrington Huge School standardized on D-76 until I changed it over to Microdol-X for reasons of economy, and of dealing with a host of real and anticipated exposure predicaments. Microdol-X is a fine fine-grain developer, a point which has been moot in the Wonderful World of E274 since XTOL came along. Your views aren’t skewed, they’re based on solid information and good craft.

I was first forced to try Microdol-X around 1976 or 1977 when I visited (out of desperation and a sense of adventure) a rental darkroom somewhere in Oak Park, and that’s all they had (it made me a nervous wreck). I imagine that  you’ve tried your share of formulae. Developers I’ve trusted, and which have rewarded me with excellent negatives over the years, include D-76, Microdol-X, HC-110, Rodinal (everybody genuflect, now), FG-7, D-23, Ethol T.E.C., Acufine, Diafine, D-19, Neofin Blue, FX-1, TFX-2 and PMK Pyro. Each delivered as promised when the film was correctly exposed for the “soup.”

This perspective comes from other e-mail correspondence:

“…there are two quite different films sold under the Tri-X name. One is an ISO-400 film with a medium toe, the other is an ISO-320 film with a very long toe. Both are available in 120 but the ISO-400 film is the only one available in 35mm and the ISO-320 film is the only one available as sheet film. The difference is in the tone rendition. Kodak has made a long toe film in sheet sizes for many years. It has lower shadow contrast and bright highlights. According to the Kodak data sheets its for use in low-flare conditions, i.e., in the studio with controlled lighting and modern lenses. The ISO-400 version is for general purpose use.

“Plus-X used to be the same way, the sheet version was a very long toe film. The tone rendition of the two is not radically different and plenty of people use the 320 version as a general purpose film, however, for some use, especially where one wants bright highlights, it has an advantage. The characteristic seems to be similar to the films sold many years ago as portrait films such as Kodak Portrait Panchromatic. To some degree the difference in tone rendition is evident by overlaying the curves for the two films but you really have to photograph the same subjects and compare the prints to see the actual difference.

“In comparison, T-Max films have relatively short toes, similar to the old Super-XX. The Tri-X 320 film has a curve which is upward deflected all along its length although not quite to the degree that the old Plus-X Pan Professional sheet film was. Note that the current Plus-X is a medium toe film for general use. I must say I think it is underrated by many. A very fine grain film with good tone rendition for many subjects.”