Sharpness VS Acutance!!

Discussion in 'Black and White' started by david_jenkins, Aug 31, 2002.

  1. Hi All,
    In another vain attempt to drive myself insane I am wanting to
    continue to grow in my understanding of effect of different
    developers on films.

    My main area of interest is how some developers increase the apparent
    sharpness of a film. My understanding of this is that this a chemical
    process rather than an optical one affecting the acutance and
    contrast of a film - some may call it edge affects on the silver
    grains. This would be shown when a neg exposed exactly the same way
    was developed in two different developers resulting in different
    tonality and contrast. I am interested in bring out all the possible
    detail and sharpness in my portraits and landscapes.

    So my question is what commercially available B&W Developers (other
    than Pyro) would increase the apparent sharpness of films?

    To fill out this basic question;
    What are the benefits or advantages of doing this and what may be the
    down sides?

    I am aware that one film and developer combination will not work for
    all subjects or situations so I would also be interested in any
    favourite combinations people my have for particular subjects -
    portrait, landscape, architectural etc.

    My currently films are Ilford FP4 Plus and HP5 Plus (with some Pan F
    and Delta films thrown in. I used Tri X for some time but not
    recently) developed in Ilford DD-X Developer at standard times and
    temps. I use both 35mm, 120 and 4x5 formats.


    David Jenkins
  2. Read "The Film Developing Cookbook," by Anchell and Troop, Focal Press, 1998. You will not regret it. It not only discusses developers, but also the characteristics of B&W films. It may be at your local library, bookstore, and of course at on-line bookstores like
  3. FWIW - and I'm sure someone will correct me if I'm wrong - accutance depends on edge effects while "sharpness" or resolution is absolute. Two tones almost indistinguishable from each other by eye can be absolutely sharp.

    Without having tried any extreme or extensive experiments I'm guessing it would easily be possible to go too far with a combination of contrast and high accutance.
  4. David, I can recommend another good book if you havent already looked at them - Barry Thornton and "Edge of Darkness" which is almost entirely devoted to discussion on this very subject.

    Best regards

  5. Anchell and Troop define acutance as "an objective measure of sharpness" on page 1 of "The Film Developing Cookbook." They distinguish these from resolution or resolving power. They say, "…resolution is a poor guide to perceived sharpness." The book has an illustration to explain what they mean by this.

    Not only do they define these terms, the book discusses them in relation to almost every commercially available B&W film and developer.
  6. David, I find that Agfa Copex Rapid developed with SPUR developer provides outstanding sharpness and acutance
    The following is an example of an 8x10" enlargement from Agfa Copex Rapid film developed in SPUR. The camera is "spy" camera Minox B
    Old Countr Inn
    The fine detail on the door is recongizedable with a magnifier, showned in a separated scan above
    Given the fact that the Minox negative is only finger nail size, the Copex Rapid + SPUR combo is remarkable
    SPUR has other developers for TMAX, Ilford Delta 100, delivering great acutance ( I haven't test my SPUR HRX developer yet )
  7. [​IMG]
    An Italian Restaurant in Unionville
    Technical Data
    Camera: Minox B spy camera
    Lens: COMPLAN 15mm f/3.5
    Film: Agfa Copex Rapid, rated at ASA 25
    Frame size 8x11 mm
    Shutter speed 1/200 sec
    Developed in Minox Tank
    Developer: 1+10 dilution SPUR Nano speed developer, 20 degree C 10.5 minutes
    Enlarger: Minox enlarger
    Print size 8x10", Ilford multigrade RC , scanned at 200 dpi
    Fine detail on mail box separatedly scanned at 2400 dpi
  8. Sharpness is a subjective sensation. Objective correlates of sharpness are resolution and contrast (MTF curves are one way to represent resolution and contrast - there are other ways). The term resolution refers to the ability of a system to separate (i.e., resolve) two closely spaced lines. The finer (i.e., the more closely spaced the lines) the system can resolve, the better the resolution of the system. Acutance refers to the abruptness of an edge. That is, does black abruptly become white or is there a border where black goes to dark grey, light grey before going to white.

    Resolution is a typically a function of an entire system - lens, film etc. Acutance is also a function of the entire sytem but can also be modified by choice of developer. Developers that are commonly considered to be 'sharp' are Rodinal, Beutler, Crawley's FX1 and FX2, tanning developers (pyro or catechol based) etc. The acutance provided by any particular developer will vary depending upon the exact mechanism used to obtain the acutance. Developers like FX1 and Rodinal rely upon the kinetics in very small areas in the emulsion providing a controlled decomposition of the developing agent - at the junction of an edge, developer is used up in the heavily exposed side and not used in the side with lower exposure. So developer diffuses across the edge to increase development at the edge of the more heavily exposed side. Similarly, brmoide released by development diffuses and inhibits development at the edge of the side with lower exposure. This results in what is typically termed as an adjacency effect. Tanning developers have very pronounced adjacency effects. In addition, they are surface acting developers (the tanned i.e., hardened, gelatin prevents developer from diffusing into the depths of the emulsion. Thus, irradiation (the spreading of light within the emulsion which destroys acutance), is reduced, thereby increasing acutance.

    The problem has apparently been in formulating a developer that can provide enahnced adjacency effects while providing a pleasing tonal rendition (i.e., the characteristic curve that determines how different luminances in the scene are translated into different greys). Most people talk of acutance developers tending to provide a 'soot and whitewash' look (I'm presuming that refers to a loss of midtone separation). In fact, the reason Crawley is supposed to have designed FX2 was because while FX1 was sharper, its tonality was considered quite harsh. Second, acutance developers tend to exacerbate any shortcoming in the system (e.g., incorrect focussing, subject shake etc). Third, many 'sharp' developers can cost you in grain - Rodinal, pyro etc can give you large grain - very sharp grain, mind you, but large. Lastly, some might argue that speed might be higher with solvent developers (which are not as sharp) since solvent action is supposed to uncover hidden latency sites. I'm not sure how much of this is strue, was true at some point but no longer is etc. I have never seen speed vary by more than a stop across developers, but I tend to expose for beefy shadow detail, so I doubt I would be the peerson to pick up on such things.

    Given all these tradeoffs, it is difficult to make prescriptions of developers for different subjects, it depends upon how you want the pictures to look. One of the best ways is probably to expose the first shot in your next six rolls to a brick wall and process the six rolls in different developers to see what the differences are.

    Cheers, DJ
  9. Heribert Schain, the inventor of SPUR develop has an article discussing
    in detail about sharpness, accutance, sharpness of contour, edge effect and grain in <p><p>
    SPUR developer is different from the so called 'compensation developer' which used edge effect of highly diluted developer to enhance accutance. Edge effect can enhance the accutance of low spatial frequency part of image, not the high spatial frequency part.
    The special power of SPUR is enhance the contour sharpess of high
    spatial frequency. <p>
  10. There are several kinds of SPUR developers for different kinds of film SPUR HRX, SLD ETC
    • SPUR Nano speed, for use with Agfa Copex, for extreme large size enlargements, from 25x to 50 x
    • SPUR HRX, enhance sharpness of TMAX 100, DELTA 100, HP5, PANF+, FP4, EFKE 25 etc
    • SPUR SLD, optimum exploitation of film speed with soft, sharply accentuated grain with highest sharpness, soft gradation and broad tonal range.
    • SPUR DOCU, for Techical Pan
  11. Rodinal majors in sharpness. But at the same time it makes the grain more prominent. I use Rodinal with Tmax 100 rated at 50 ASA. TMX has extremely fine grain so even with Rodinal grain is not an issue but it gives superb sharpness, detail and smooth tonality.

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