High accutance developers and resolution...

Discussion in 'B&W: Film, Paper, Chemistry' started by aldevo, Jun 14, 2009.

  1. aldevo

    aldevo Member

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    Every once in a while, I'll come across a posting on APUG or photo.net along the lines of..

    [tired old film/developer combo thread omitted]

    "...and be sure to use a high accutance developer to maximize resolution"

    The posters act as if fine-grain developers contained all manner of evil silver solvents that happily munch away at your negative, turning your grain to mush and obliterating fine detail.

    I'm not a photo-chemist, but is it possible that the posters have got this backwards or are - at the very least - exaggerating?

    From the very little I have read about adjacency effects (e.g. so-called "border" and "fringe" effects) it would seem that these might actualy result in diminished resolution in the immediate area of the image in which they occur. Applying an exaggerated unsharp mask to an image in PhotoShop also seems to suggest this could be true.

    At the same time, I know that all the metallographs that were produced in my grad school lab work back in the mid-90s were developed using D-76c and I understand that this developer is very commonly-used in scientific work. Being from the D-76 family, I doubt it's considered a "high-accutance" developer...but I suspect that scientists researchers aren't keen on the loss of image resolution in their work.

    I have not seen any scientific findings on the web regarding the benefits of accutance developers for resolution.

    Does anybody any such findings that they can share?
     
  2. Bruce Watson

    Bruce Watson Member

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  3. alanrockwood

    alanrockwood Member

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    Then what's the point of having a discussion group if the best advice is to go read a book?
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    I have made a rather extensive series of posts on macro and micro edge effects and the contrast effects that also take place. You may want to look them up to further extend your understanding of this.

    PE
     
  5. CBG

    CBG Member

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    If something is the best advice, then why would the OP want less.

    In the case of suggesting "The Film Developing Cookbook", the OP got a very good piece of advice. The book contains far more information than would be manageable to communicate within the constraints of a forum.
     
  6. dpurdy

    dpurdy Subscriber

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    As I understand it from what I have read, part of the sharpness increase of developers like Beutlers is that they do not develop as deeply into the grain of the film. They develop only the surface of the grain layer which results in less defraction of the light rays or less development of the diffusion of the light rays from going through the film grains. In fact I am going to just get my book and copy what it says:

    By Gerald Koch
    Any discussion of high acutance developers should begin with a definition of acutance. Unfortunately this term is not easily explained. However for the purpose of this article we can think of actuance as the scientific name for what the eye perceives as sharpness. Some years ago, when emulsions were grainier than they are today, developers containing very active silver halide solvents such as thiocyanate and phenylenediamines were popular. Their popularity was not universal since it was found that the reduction of the granularity was at the expense of sharpness. As far as the eye is concerned, it is the final critic in any photographic process, a sharp print is obtained by favoring acutance over grain.

    The acutance of an emulsion is related to many variables notably it's thickness, grain size and contrast. Of these the first seems to be the most important. In order to understand this, let us consider a single ray of light from a point source striking two photographic emulsions, a thick one and a thin one. As the ray passes through each emulsion it is scattered by the halide grains. A similar scattering enables us to see the projectors beam of light in a smoky movie theatre. If we developed the two films and looked at each image and it's cross section they would appear as below

    (at this point there is a drawing showing a beam of light going through a thin emulsion with no scatter and a beam of light going through a thick emulsion with a spreading out of the beam)

    The result of scattering in both cases is to make the image of the point source larger than it should be if the emulsion were infinitely thin. Obviously, the thicker the emulsion the more the image is spread and the fuzzier are it's edges. This is why, all other things being equal, a print from a fast film cannot be as sharp as one from a slow film, In order for the fast emulsion to be fast it must contain more silver halide and therefore must be thicker.

    Now we can improve on the already considerable sharpness of modern slow speed films by making them thinner. Physically we can't do this but chemically we can, buy using developer which works only on the surface of the emulsion. Such a developer must be very active to offset the loss of sensitivity resulting from using only a portion of the emulsion layer. But in order to prevent the excessive contrast the developer must be compensating. That is, it must stop working in the regions of the high exposure once a certain density is reached while still continuing to work in the regions of low exposure. A simple way to solve these two problems is to use a very dilute solution of a very active developer. Because of the high dilution the developer will be exhausted at the sites of high exposure, keeping the contrast at the proper level. Being very dilute it will have little effect on the silver halide in the interior of the emulsion. In addition high acutance developers usually contain no bromide; the bromide released during development being used to restrain the action in areas of high exposure, thus increasing the compensation.

    Pioneer work on the technique was done by Willi Beutler working for Tetanal-Photowerk in Germany. His formula, originally published in the Leica News, together with some high acutance formulas appearing in the British Journal of Photography and in Mason, Photographic Processing Chemistry are given in the table below.

    (at this point the article lists Beutler, FX-1 FX-13 and Mason and the formula for each using Metol, Sodium Sulfite, Potassium Iodide and Sodium Carbonate. The formulas all use just these chemicals though they vary quite a bit)

    Dennis
     
  7. dancqu

    dancqu Member

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    Yes the article was written by G. Koch and is included in
    Patrick Dignan's Classic B&W formulas.

    The developers you've mentioned are very dilute, very active,
    and metol based. I believe metol is the chosen agent due to it's
    reduction in activity in the presence of bromide. That reduction
    in activity aids in achieving additional compensation. Dan
     
  8. Bruce Watson

    Bruce Watson Member

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    Simple questions don't always have simple answers. In this case the answers are so complex that it literally takes a book to adequately explain them all.

    If you think you can do better, have at it.
     
  9. gainer

    gainer Subscriber

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    Rodinal is one developer that can show infectuous development. You can look "infectuous development" up in "The Theory of the Photographic Process." The symptoms will be seen if you photograph a resolution chart which has black and white lines of equal width and the negative shows black lines wider than clear ones. This is a distortion that in certain cases looks like increased acutance, but may actually decrease resolution. In an extreme case, the lines can merge.
     
  10. RalphLambrecht

    RalphLambrecht Member

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    My response may not be precisely what you're looking for, but hopefully it helps to clarify a couple of thinks.

    To me, sharpness (or image clarity) has three components, resolution, acutance and contrast. With 'acutance' I mean 'edge contrast' and with 'contrast' I mean overall image contrast. Film development has a large influence on acutance and contrast but only a minor influence on resolution, which is mostly coming from a good lens combined with a fine-grain emulsion.

    Certain film developers work better for acutance than others, but one very important aspect of acutance is the development technique. Optimum acutance requires standing development. Rotation and even 30s-interval inversion techniques destroy most of what a good acutance developer can do.

    By the way, subjective image evaluations clearly show that there is an importance ranking for the three components of sharpness.

    1. contrast (high)
    2. acutance (high)
    3. resolution (low)

    A high-contrast image looks sharper than a soft one, and high acutance is often mistaken for resolution (that why unsharp masking works). Resolution is not necessarily seen as sharpness. Indeed, a high-contrast, low-resolution image is often perceived as being sharper than a low-contrast, high-resolution image. If you have a choice, go for acutance and contrast and forget resolution (it works for digital, it will work for you).

    To prove the point about digital, I have not measured a on-chip resolution of more than 60 lp/mm on any digital camera, but good 35mm lenses combined with fine-grain film can easily achieve over 100 lp/mm. Still, you would be hard pressed to see the difference between the two on an 8x10 print. Why? At that magnification, the resolution of both is beyond human detection, but increasing the acutance of the digital image is as easy as a mouse click. The story quickly changes in favor of film at larger magnifications.
     
  11. Alan Johnson

    Alan Johnson Subscriber

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    My results with T-max 100 film in Xtol 1+0 (solvent) and FX-1 (Acutance) don't show much difference in resolution.Photomicrographs of negatives of test chart, numbers on chart are resolutions in line-pairs per millimeter.
    Lens was Canon ef 50mm f1.8 at f5.6.
     

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  12. Photo Engineer

    Photo Engineer Subscriber

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    Considering the size and contrast differences, it is a bit hard to judge.

    PE
     
  13. aldevo

    aldevo Member

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    I do own a copy.

    While it explains the difference (which is rather obvious) between accutance and resolution; it does not present any useful information on how developer type affects resolution.

    While Bill Troop is a photochemist, the primary author (Steve Anchell) is not.
     
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  15. aldevo

    aldevo Member

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    Very interesting point about the relative importance of the three components of sharpness.

    I have read on the web that with the emergence of thin emulsion films in the 1950s, lens designers shifted their emphasis to optimizing contrast across the frames, rather than outright maximization of resolution.
     
  16. sanking

    sanking Member

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    Developers that limit the migration of silver halide during development may result in a more precise reduction. A developer that tans and hardens the gelatin during development may reduce the effects of irradiation and infectious development (spreading of silver development beyond the exact image boundaries). Pyro staining developers also tan the gelatin, but there are other reducers that also tan and harden gelatin. Ron may want to mention a few.

    To obtain the maximum resolution requires that the film be given correct exposure and development. To much of either will result in spreading of the silver development outside of the image area.

    Sandy king
     
    Last edited by a moderator: Jun 15, 2009
  17. mrred

    mrred Subscriber

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    Not entirely. Digital has a linear grid for the 'dots'. Film grain moves with the light and processing, thus is uneven in it's distribution. This gives the blacks in film a much richer look and the greys in digital a much more linear graduation.

    Depending on the shot, film and digital will show different aspects of the lens. The same, yet different.
     
  18. aldevo

    aldevo Member

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    Exactly the sort of response I was hoping to get.

    I will look them up. Thanks, PE!
     
  19. voceumana

    voceumana Member

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    Aldevo,

    I think you have it exactly right, except that D-76 is considered a moderately fine grain developer rather than an accutance developer. For the best resolution, you probably don't want the highest accutance developer. Best resolution is usually acheived with a lower contrast light-to-dark transition, whereas highest accutance is acheived with a higher contrast light-to-dark transition.

    Charlie Strack
     
  20. Photo Engineer

    Photo Engineer Subscriber

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    Developers can be maximized for any two of the following: Grain, sharpness and speed. Normally, you cannot maximize all 3 but you can strike a happy medium.

    Alan's experiment above is one of the best comparisons I have seen on APUG in spite of my comments. More like it should be done to "prove" a theory or observation.

    PE
     
  21. sanking

    sanking Member

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    But is not the lens the limit of resolution in Alan's test, not the developer? I have done tests by contact printing high resolution chrome on glass targets and with Tmax-100 I was able to get somewhere around 160-180 lines per mm with pyro staining developers.

    Sandy
     
  22. Thomas Bertilsson

    Thomas Bertilsson Subscriber

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    I agree with Ron. These results are technical and can usually be measured. Unless it's measured it's subjective and fairly useless for anybody else.
    I do feel that people put too much energy and thought into film developers. Pick one and work with it. By varying your technique, evaluating your results, and above all - printing your negatives often, you learn a lot.
    The other week I shot two rolls of Kodak TMY (the old kind) using a 35mm camera. I processed one roll in Rodinal and the other in Xtol. According to what everybody claims they observe with these two developers, the difference in grain should be huge. In reality, in the resulting 11x14 prints, the difference (to my eyes) is really negligible. Sharpness was very similar too. I used a Rodenstock Rodagon enlarging lens, which is an OK lens, so no sub-par equipment either.

    What I'm getting at is that if you're truly interested in resolution, sharpness, grain, acutance and all that, at least make an evaluation based on how it makes a difference for you in practical terms before you take it too far. I found, by comparing prints of the normal size I make them, that I don't really care whether I get the look of the Rodinal or the look of Xtol. As an artist the difference between them is not even close to feeling important, that's how subtle the difference is. It may be different for you, but it's worthwhile comparing prints before you get overly concerned with which film developer you use.

    - Thomas
     
  23. Photo Engineer

    Photo Engineer Subscriber

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    Sandy;

    A true test would be a contact print on a negative and positive definition chart such as found in the Edmond Scientific catalog. They are depositied metal images and are as sharp as you can get.

    This eliminates all optics.

    But, in the comparison tets Alan did, the lens would cancel out all other things being equal. And, since you can see differences in spsite of my comments, then the differences are not the lens.

    PE
     
    Last edited by a moderator: Jun 15, 2009
  24. Alan Johnson

    Alan Johnson Subscriber

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    The lens is partly controlling the resolution according to Mr Puts:
    http://www.imx.nl/photo/Film/Film/Film/page35.html
    Still, both Xtol (solvent) and FX-1 (acutance) get about 100 lppm in my test with T-max 100.By printing with an enlarger resolutions this high can be mostly transferred to paper,not so with consumer scanners IMO.
     
  25. Photo Engineer

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    Alan;

    It may be limiting, but if it cancels out completely, then it has no influence. So all else being equal, there is no problem other than the size, density and contrast. And, these are minor when compared to other "tests" where someone merely says the results looked good when I eyeballed it! (single test, no comparison, etc. etc.)

    PE
     
  26. sanking

    sanking Member

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    Alan,

    It is hard for me to see much difference in the results. The FX-1 negative appears to have better resolution but more grain. Is that what you are also seeing?

    My own experience in shooting targets with cameras is that film flatness can be enough to explain any differences when resolution is already so high. It takes really good technique to shoot a target as you did and get 100 lppm.

    Sandy