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  1. #1

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    Stain, dye clouds, sharpness - question for the chemists

    Warning - this is not a Pyro war. Just a question about the dye formed. And it could possibly apply to colour/chromogenic films. Not sure.

    So, we "know" that generally, Pyro/Cat developers are considered sharp. There are a variety of reasons for this including low solvent action (at least in staining formulas), adjacency effects, tanning etc. In a staining formula, since the image is composed of silver and dye density, why doesn't the dye cloud formed around each silver grain (or group of grains) reduce sharpness? Isn't the dye cloud effectively "spreading out" around the grain of developed silver?

    Michael

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    It actually does reduce sharpness. The same thing occurs in a true chromagenic film. This can be seen in photomicrographs of stained negatives. If you think about it this has to occur because if the stained area was the same size as its grain then you wouldn't see it. The silver grains would act as masks. How far the stain extends past the silver grain is a function of the developer composition and the diffusion rate of the oxidized developer. This is why staining developers are not recommended for SF films. For MF and LF format negatives the loss of sharpness is countered by the reduced appearence of the grain. But then grain is really not a problem in these formats.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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    Thanks, Gerald. Makes sense. After all you can't get the "grain masking" effect without the dye spreading beyond the edges of the silver grains, clumps of grains etc. Although I have to say in my experience the grain masking effect is less than one might expect, even with fairly heavy stain.

    Interesting how formulators of staining developers often refer to the grain masking effect, but I can't recall any mention of any offsetting effect on apparent sharpness or possibly even resolution. You're apparently supposed to have your cake and eat it.

    Thanks
    Michael

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    Michael, staining developers are one of those aspects of photography that has taken on semi-religious or mystical overtones.

    The stain helps make the edges of the grains less pronounced.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  5. #5
    Ian Grant's Avatar
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    The problem here is that theory and hypothesis aren't the same as the actual practical results. Not all staining developers are the same the older more concentrated types don't give fine grain but their degree of acutance/sharpness from the tanning effects made them ideal for contact prints.

    The newer highly dilute Pyro developers are quite different, they give sufficient staining and acutance without compromising grain etc, it's a balance.

    Quote Originally Posted by Gerald C Koch View Post
    The stain helps make the edges of the grains less pronounced.
    Pyrocatechin is used in fine grain developers, on it's own or in combination, sometimes with levels of sulphite that suppress staining, so a developer like Pyrocat HD/MC would almost certainly give good fine grain regardless of the staining.

    Maybe the staining's sufficient t mask the edges of the grain but it's not having a detrimental effect on the micro contrasts which affect the fine details.

    Ian

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    The question of resolution can be argued ad nauseum until someone steps up and runs a series of well designed and executed experiments comparing a staining developer against an acutance developer using a standard resolution chart.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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    Ian Grant's Avatar
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    Quote Originally Posted by Gerald C Koch View Post
    The question of resolution can be argued ad nauseum until someone steps up and runs a series of well designed and executed experiments comparing a staining developer against an acutance developer using a standard resolution chart.
    It's the final prints that count not testing with resolution charts which only tell you part of the story. I'm just cutting mats for 50+ exhibition prints all from Pyrocat negatives and it's the balance of sharpness (definition), tonality etc and rendition of detail in highlights and shadows that's important to me. I should add my Pyrocat negs scan wee to.

    Ian

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    If no one runs the experiment I suggested then the argument about the resolution of staining devellopers is a moot point and this thread is immaterial.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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    Ian Grant's Avatar
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    Quote Originally Posted by Gerald C Koch View Post
    If no one runs the experiment I suggested then the argument about the resolution of staining devellopers is a moot point and this thread is immaterial.
    But it doesn't address the realities, I guess I've done the tests and seen the results for myself but not in a lab/false situations.

    I tried and used many of the older high acutance developers, Hyfin, Acutol-S and a few others. sure they give superb acutance and sharpness but grain isn't fine and tonality is harsh and you can lose fine detail.

    Real life testing is far more important.

    Ian

  10. #10

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    Part of the "magic" of staining developers when compared to chromogenic films is that the stain actually hardens the film adjacent to the area of development. This hardening is said to reduce the amount of growth/spread of the silver, making the image sharper.

    Chromogenic films just generate dye clouds, without the benefit of the hardening effect.

    I believe Sandy King posted info on resolution tests he had done with his developers here years ago.

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