Acutance Films?

Discussion in 'B&W: Film, Paper, Chemistry' started by sanking, Apr 1, 2006.

  1. sanking

    sanking Restricted Access

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    I have seen the use of the term "acutance" to describe modern B&W films?

    What are the characteristics of a modern B&W film as opposed to a traditional one? Is it merely a question of single versus multple emulsion layers, or are there other more important considerations. And which films are modern? I assume that the T-grain emulsion films such as TMAX-100 and TMAX-400 would be considred modern. But what about a film like FP4+ that has been around a long time more or less in its present incarnation? Would it be considered a traditional or modern film?

    Sandy
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Sandy;

    Among onther things:

    An acutance film is one with reduced internal reflections. This is accomplished by adding an acutance dye to the film. This dye decreases speed though, so you need a fast emulsion with fine enough grain to allow the use of added dyes to improve sharpness without a severe penalty in grain.

    It has lower turbidity by means of having more transparent grains, thereby reducing scatter. This is often achieved with very thin t-grains, thinner gelatin layers, or lower levels of coated silver with beter developability (a greater % of active grains vs 'dead' grains).

    It has higher edge effects by using higher iodide levels or having more iodide on the surface of the grain. It can also achieve this by having inhibitors in the film that are released by the emulsion during development. An example of this is a chromogenic B&W film or any color negative film.

    Hope this helps.

    PE
     
  3. sanking

    sanking Restricted Access

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    PE,

    Thanks for the useful information.

    What you say about the use of thin t-grains and thinner gelatin layers to decrease turbidity makes sense. But what is the mechanism that results in less internal reflections with the use of a dye?

    Sandy
     
  4. Photo Engineer

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    Imagine the light being reflected an infinite distance within the coating by bouncing off old style K (klunker) grains. They can then travel quite a distance (in microns) from the 1 micron grain in a high speed K-grain film. This could cause exposure where you don't want it to take place. The absorbing (acutance) dye attenuates this reflection but at the same time reduces speed.

    The dye also trims speed so that ISO can be more constant from batch to batch.

    These dyes are the colored dyes that wash out of films when you dump the first solution out of your developing tank.

    They are also used in color paper to trim the speeds of the various layers and improve sharpness in the multilayer structure.

    A common dye, used in Matrix Film and also used in old blue sensitive films was Tartrazine. However, since the eye is not sensitve to yellow image sharpness (we see the sharpness of mainly cyan and magenta dyes), it is not really necessary except in Matrix Film or B&W films only sensitive to blue. If you have an ortho or pan film, then you need to use mixtures of dyes. That is why the 'runoff' from the first processing solution is brown or green. Those are the dyes chosen to optimize that particular film for sharpness plus trim speeds.

    PE
     
  5. Bruce Watson

    Bruce Watson Member

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    One would think that thinner layers also helps just due to the fact that the layers are thinner. The layers are still 3D, and there are active grains distributed stochastically in X, Y, and Z. The Z dimension is interesting because grains are not in line as light penetrates the depth of the coating, allowing exposure of overlapping grain structures. The effect on the image would be of larger grain, and lower accutance. That is, less of an ability to image a thin straight line due to the overlapping grain structure; the line would be bumpy and would "blur" if you will.

    Then again, I could be completely wrong. Wouldn't be the first time. Won't be the last either. What say you, Photo Engineer?
     
  6. Photo Engineer

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    If there is no turbidity, and the light strikes at a 90 deg angle, then the T-grains may be considered to be acting as half silvered mirrors with the light passing through or exposing, and as the light penetrates deeper and deeper into the film, it is attenuated. This takes place due to the fact that grains are stacked.

    Of course, with turbidity and reflection (scatter) what you say is true also. as some grains are not stacked, or light hits an edge and etc.

    In any case, the edge effects produced during development assist to 'trim' up the edges.

    The simple test of the ratio of the effect between all of these is to make white light knife edge exposures and soft x-ray exposures (these latter will not be affected by any scatter or reflection). The ratio of the measured line spread in the two sets of exposure vs desired line width as actually found on the chart used will give you a measure of the ratio of chemical to physical effects, and the size at which the effects are maximized for sharpness will show what format (35/MF/LF) the film will be most effective at. Usually, a design goal is to have these adjusted so all 3 formats will be optimum.

    Of course, this is not always possible, but a happy medium can be obtained, which is what we always are faced with - a series of compromises for the best of all of these.

    PE
     
  7. Alan Johnson

    Alan Johnson Subscriber

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    Film/developer combinations that show the adjacency effect are said to have high acutance (strictly acutance is the edge density slope).It's possible to estimate the adjacency effect by photographing a light grey card on a black card,stand developing in rodinal 1:200 for 90min and making a 10x enlargement of the grey/black interface.Adjacency effect shows as a light line at the interface.
    Some films that show the effect:Adox CHS 100, Plus-X, HP5, Tri-X.
    Some films with little or no effect (hard to tell):T-max 100, Delta 100, Delta 400, Pan F, FP4, Lucky SHD 100 New, Acros.
    In my test the word acutance separates the films quite well, the word modern not very well.
     
  8. dancqu

    dancqu Member

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    [QUOTES=sanking]
    "I have seen the use of the term "acutance"
    to describe modern B&W films?"

    Acutance, hardly a "modern" term. Going so far
    back as 70 years ago Willi Beutler was formulating
    high acutance developers for the slow thin emulsion
    films of the day. Adox KB14 or a film of it's type may
    have been one Tech. Pan was perhaps 30 years
    latter; 40 years ago?

    "What are the characteristics of a modern B&W film
    as opposed to a traditional one?"

    Incorporated hardeners. Automated machine processing
    spurred their incorporation. T films are noted for their
    high temperature endurance. When were they
    introduced, 15 - 20 years ago?

    "And which films are modern?"

    Modern, in my mind, equates with incorporated hardeners.
    As I've mentioned the spur was high speed high temperature
    machine processing. In that respect, and from what I've
    read, T films are more recent modern films.

    "But what about a film like FP4+ that has been around ..."

    FP4+, is a modern film but not one which would generally
    be considered a purely acutance film.

    In the beginning their were soft emulsions, acid stops,
    and hardener incorporated fixers. Traditional films should
    receive in-the-beginning processing. Dan
     
  9. Photo Engineer

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    I think that the point here is that there are HA films and NA (normal acutance?) films and HA developers and NA developers. Along with this are all of the degrees and combinations of all of these.

    The use of these combinations is what leadz to the infinite variety of results we get with analog film, and also leads to the reason we disagree sometimes as to result. In any event, this almost infinite variation is what enchants me about film vs digital which is like driving a nail into the creativity processes and fixing them to someone elses desired result.

    The near infinite variations that can be obtained were known for years at EK and that is why there were so many films and so many film developers. This was not unique to EK, as other companies did much the same.

    PE
     
  10. sanking

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    I was not surprised by the use of the term "acutance" to describe developers, which as you observe has been used for decades, but as an adjective to describe film. The term has not been widely used, at least from my readings, to describe films. Even though it is clear that modern T-grain films such as TMAX-100 and TMAX-400 have much better native resolution than traditonal films of same ASA such as Plus-X, FP4+, TRI-X, HP5+, etc.


    Sandy
     
  11. sanking

    sanking Restricted Access

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    Interesting test. Could be also useful to test developers?

    Sandy
     
    Last edited by a moderator: Apr 1, 2006
  12. Alan Johnson

    Alan Johnson Subscriber

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    My take is that there was an acutance era with films like Panatomic-X but after the coming of T-max 100 etc it mostly went. T-max 100 showed no sign of adjacency effects in my test and I would not call it an acutance film.But some may use the term acutance more generally to mean some form of sharpness.My guess is that the test may pick up films with acutance era properties.
    For testing developers I would use the test with Tri-X. I always think there may be some as yet undiscovered developer giving improved sharpness,especially with stand development.
     
  13. Bruce Osgood

    Bruce Osgood Membership Council

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    This is a very interesting thread and comes up at a very opportune time for me. I'm looking for film/developer for 35mm neg that will enlarge to greater then 8X10 and retain the crispest lines the lens will give.

    I just tried Acros in the Willi Beutler developer to no success.
     
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  15. Peter Schrager

    Peter Schrager Subscriber

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    Bruce-you should try the Acros with Rodinal; continuos; stand or semistand.
    Maybe it will give you what you want. Backside is go to 120 film and start to live. I'm getting incredible prints now with Acros+Rodinal 1:100 in the 120 size.
    Haven't touched my LF gear for quite a while now I'm having so much fun with this combo.Printing back on Gallerie Graded Paper with outstanding results. Who would have ever thought?
    Best, Peter
     
  16. Bruce Osgood

    Bruce Osgood Membership Council

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    Thanks Peter, that is the nex step: RODINAL. I've been draging my feet using Rodinal until there is a supply in Adoramma/B&H. The little bit I have on hand I've been guarding.
     
  17. Peter Schrager

    Peter Schrager Subscriber

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    Screw B+H-they don't have it. Call up Freestyle and order it right now!!
    Peter
     
  18. Mark Layne

    Mark Layne Member

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    Folks seem to be confusing developer induced acutance with acutance inherent in a films design.
    Mark
     
  19. df cardwell

    df cardwell Subscriber

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    Acutance traditionally refers to the potential to image low frequency data at high contrast. It is determined by the film, the camera system, and the Subject contrast. The potential acutance of an image, therefore, is determined prior to development.

    Acutance developers, FX-1 for example, are intended to enhance in various ways the acutance of the latent image. It is, in its effect, like the degree of an image's magnification; the greater the magnification the easier it is to see the detail inherent in the negative. An acutance developer will make it easier for the viewer to discern the low frequency data inherent in the negative.

    Where I get confused is comparing films evolved from the '50 and '60s to T-grain films. The native acutance of T-Grain films is so much higher than old films that it defies comparison. Yet new films tend to be resistant to the 'FX' we tend to associate we good acutance: edge, adjacency, etc., etc., etc.

    The problem I think comes down to application. I have two 11x14 images before me, shot on 35mm under identical optimal conditions; one on TMY, one on FP4+. From a close viewing distance, both negatives show the coarse detail of subject’s eyebrows and fine facial hair with clarity. The difference is in the secondary aspects of the image. TMY has slightly greater native acutance than FP4+, and to equalize the images, I needed to use a moderate FX developer with the FP4+.

    In a side to side comparison, the acutance is similar, but the FP4+ is slightly grainier.

    But things change with a different application. Making an 8 x 10 contact print of the same portrait subject, made on Tri X, the fine facial hair is not visible without giving moderate to heavy FX development to the Tri X.

    On an identical TMY negative, it would not surprise me if the vastly more acute T grain film would not make as suitable an image. Without enlargement, it is essential to grossly exaggerate the acutance of the image in order to give the impression of sharpness and detail to the print.

    Contact printing, we are usually interested in extra low frequency data, and lacking the ability increase the viewer’s discernment of the image detail by enlargement, we can only increase the separation of the design elements by increased local tonal contrast.

    Weston demonstrated this technique by not composing in adjacent tones: the lighting generally provided the necessary contrast, not the pyro.

    But shooting in flat light is a very important thing for contemporary photographers to do. It is still a largely undocumented world, which presses material and technique to the limit. Increasing tonal contrast is essential to it’s success.

    Perhaps, however, we could agree upon a word to describe the exaggerated tonal separation needed for contact printing low contrast scenes.

    Acutance, describing something else entirely, is already taken.

    Local contrast ? I dunno.

    .
     
  20. sanking

    sanking Restricted Access

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    DF,

    Great summation.

    But don't we already have a term to describe the exaggerated tonal separation needed for contract printing low contrast scenes? I call this micro-contrast, and from what I have read of his working procedures, the creation of micro-contrast appears to be at the heart of Steve Sherman's work with semi-stand development techniques.

    Sandy
     
  21. Photo Engineer

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    Sandy, in contact printing from a LF negative, we are relying on macro contrast but when printing an enlargement from a 35mm negative we are relying on micro contrast.

    The contrast reported in normal H&D curves from standard charts is always macro contrast.

    The reason for this is and an example might be to use a wire between two poles photographed in LF, MF and 35mm. I have used this example before.

    In 35mm, this wire may be 1 micron across, in MF it may be 10 microns, and in LF it might be as large as 100 microns. Each of these, if presented as a series of steps on a 1m, 10m or 100m step wedge gray scale would give 3 different contrast images. If they were compared to the normal H&D curve, the step wedge from the 100 m line would normally be closest, but not equal to the normal curve.

    In addition, the width of these lines would vary from the ideal due to scatter and development effects and this is why the curves constructed from the densities would also differ.

    In any event, the larger the negative, and the smaller the magnification during printing, the easier it is to judge contrast and sharpness. Now, this discounts extremely fine detail, but that is a matter for observation on the final print with a loupe.

    So, acutance boils down to the finest resolvable item at standard viewing distance for a given print, which is about where you hold a book when you read it. If you cannot see a difference at standard viewing distances, in a print, then there is no significant difference.

    There are several fine articles about this in the photographic journals. One that I like on the subject was written by Mike Kriss and has micro and macro curves illustrating these points.

    PE
     
  22. sanking

    sanking Restricted Access

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    I certainly am not surprised that you are getting great results from the Acros+Rodinal combination, but my take on this is that the Acros is doing most of the heavy lifting. I am certain you could get excelent results with Acros and a number of other acutance and high acutance developers because it is an outstanding film.

    As for getting optimum quality in enlargments over 10X, film choice would be my first and most important consideration, since choice of develper has a relatively much smaller impact on film grain and resolution than film type.

    Sandy
     
    Last edited by a moderator: Apr 3, 2006
  23. rbarker

    rbarker Member

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    Interesting thread. Thanks, Sandy, for bringing it up.

    I like DF's summary, and his use of the term "local contrast". For me, local contrast describes the separation of the edge of the leaf, for example, from its background, or adjacent tone, whereas "micro-contrast" describes the ability to see the texture of the leaf's surface.
     
  24. sanking

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    PE,

    I know this is normally the case. However, my understanding is that the use of the term micro-contrast is appropriate to describe the incease in apparent sharpness in contact printing LF negatives that results from the greatly enhanced edge effects produced by some film/developer/agitation combinations.

    Sandy
     
    Last edited by a moderator: Apr 2, 2006
  25. df cardwell

    df cardwell Subscriber

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    Thanks Ralph.

    Notice how Mark said it in 15 words ?

    It's gratifying to struggle to put into words what I THINK I know, and then have you guys pick it up and carry it forward.

    Ron & Sandy: thanks.
     
  26. Photo Engineer

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    Sandy;

    I agree to some extent. Here is the problem. If you see these effects at 1, 10 and 100 microns, but you are contact printing from an 8x10 or 11x14 negative, that effect may not exist with a 1000 micron line. In other words, edge effects tend to decrease in relative importance as size of the item increases.

    Therefore, micro contrast and sharpness differences collapse towards the macro equivalent as the original image size increases. If you had a life size negative and made a contact print from it, edge effects would be useless and any image enhancement would be invisible at standard viewing distance for this image which would be several feet away. The edge effects would just be too small to be significant.

    In addition, if you use a positive and negative resolution chart or read the knife edge exposures forward and in reverse so to speak, you measure fill in and bloom aspects of the micro image. These also vary as a function of size of the original object and the amount of edge effects.

    PE