The negative density range as derived from the paper LER is more of an aim than an absolute. There isn’t a perfect correlation between the two. Popular photo books aren't big at caveats and tend to simplify this relationship which can lead to the conclusion there is. Serious sources have never claimed a perfect correlation. Jones, who developed the method, in one of my favorites of his quotes wrote, “The procedure followed in obtaining a relationship between DR and LER may seem forced and artificial. This we grant, and it must be borne in mind that the print quality obtained by its use will not be the highest quality. But what other course is there to follow? Either we must make the best of a somewhat imperfect relationship or face the prospect of having no criterion whatever for choosing the paper contrast grade.”
His conclusion shouldn’t surprise anyone. It’s not that psychophysics isn’t an effective science. It’s just that there are too many variables involved with the determination of print quality to fully express in a few digits. Here’s a graph from some of Jones' tests.
The graph shows the DR of the negatives, horizontal lines, printed on a grade two paper that were judged as high quality prints. They don’t all fit neatly within the defined limits of the print. The type of subject matter as well as the amount and distribution of the tones are a couple of factors that makes it impossible to predetermine print quality with any precision.
But of all the various methods Jones explored, this one tends to produce better results in the greatest number of circumstances. It gets you close enough to work with. It's statistics. I don’t know about everyone else, I only develop in one stop increments, and I don’t believe most scenes are considerate enough to have luminance ranges in perfect one stop increments. Even if there was a perfect correlation between DR and LER, it would be unrealistic to believe it could be achieved in most cases because of all the variables involved. Flare along would make this impossible.
There is another inconsistency with the DR / LER relationship that most books don’t discuss and that Michael has observed. The DR / LER relationship chances with the scene’s luminance range. Jones writes, “for the soft papers, the density scales of the negative (DR) should in most cases exceed the sensitometric exposure scale of the paper (LER), whereas, for the hard papers, the density scales of the negatives should in most cases be less than the sensitometric exposure scale of the paper (LER).” In other words, it’s not only acceptable, but preferable to have a slightly contrastier negative for contrasty scenes and a slightly flatter negative for flatter scenes.
Sure it's not perfect, but what other course is there to follow?
Last edited by Stephen Benskin; 09-22-2012 at 03:58 PM. Click to view previous post history.