Film Characteristics Curve - Understanding

Discussion in 'B&W: Film, Paper, Chemistry' started by cjbecker, Oct 21, 2011.

  1. cjbecker

    cjbecker Member

    Dec 9, 2010
    Medium Format
    I am trying to figure out how to fully read a film characteristics curve chart.

    I understand how to read the toe, the shoulder, and also the part in between them. I understand a long toe with not have as much contrast, and or detail, in the blacks and shadows of a print as a short or straight toe will. Also the same with a shoulder that is long. It will just blow out anything white above it in the print, compared to a short/straight shoulder. Also the section between the toe and shoulder, steeper=more contrast, less steep=less contrast.

    correct me if i’m wrong with whats above.

    The thing that I am not understanding is why a film that has a long toe and a straight shoulder (txp) is harder to print then a negative with a long toe and long shoulder.

    I think it would be easer to print a negative with a long toe and a straight shoulder. Is the reason because they are trying to preserve detail in the shadows?

    Thank you in advance.

    And if i’m completely wrong, don’t be soft.
  2. Doremus Scudder

    Doremus Scudder Member

    Sep 10, 2002
    Oregon and Austria
    4x5 Format
    Think tonal separation. The steeper the curve, the more tonal separation.

    Now think: the human eye has great tonal separation for highlights or in bright light, but lousy tonal separation for shadows and in dim light.

    Now, take a long-toe film, make a print (where the shadows will be compressed in tonal separation) and display it in low light.... You get the idea.

    That said, there are a ton of subjects that don't need great shadow detail and a lot of us who love shadow detail that use TXP (me included). So it's not all that cut and dried. I solve the TXP toe problem by simply overexposing the film to get more of the shadows up onto the straighter portion of the curve.

    Many portrait photographers love films with long toes because they suppress the unwanted detail in the shadows but, as a reward, give more pleasing separation in the mid-tones, where most of the interest in the photo lies.

    Keep in mind, that there is a rather "fixed" range of tones between maximum black and maximum white. It is the distribution of those tones that can make a photo sing, or flop. I love shadow detail, but I also love lots of mid-tone separation and delicate whites. For me, TXP works fine with a rather high placement of the shadows.

    It all depends what you want.


    Doremus Scudder
  3. polyglot

    polyglot Member

    Jun 12, 2009
    South Austra
    Medium Format
    Here is where you're confused. A long, flattened, shoulder will give you detail in the highlights out to crazy-high exposures, but with poor contrast (tonal separation). The highlights can look dull. This is what you get with a compensating developer where (typically) bromide appearing in the highlights retards the developer and brings the highlights under control - think semi-stand Rodinal at high dilution.

    A short, sharply-clipped shoulder might be what you're thinking of and yes, it will clip highlights. Most negative films don't really do this though as they're typically very forgiving of overexposure.

    A long straight shoulder means that you can overexpose as much as you want and you won't be able to tell (other than by increased grain) by looking at the print - the highlights retain all of the detail. Obviously if you print at too-high contrast or not dark enough, then your print will not contain all of the highlight detail that is on the film.

    It's not that a long straight curve is hard to print as such, but it's easier for the neg to contain a lot more dynamic range than you can fit into a print without dodges and burns. You may need to make a decision to clip highlights at a certain point, whereas if you'd used a compensating developer, you could have fit a longer tonal range in (with no loss of detail) at the cost of reduced highlight separation and a flatter-looking print.

    A long-toe, steep-shoulder film looks good because it has a lot of highlight separation; the print will sparkle. It is for this reason that I love IR820 - it has a dramatically up-swept characteristic curve.