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  1. #21

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    Quote Originally Posted by Jed Freudenthal View Post
    High definition, as it is defined nowadays, (not just in photography) has an MTF close to 100% over the entire range of relevant spatial frequencies. In practice, the MTF will fall off somewhat at higher spatial frequencies. A developer for scientific applications should always be high defintion ( image distortion as small as possible). For developer/film combinations see publications of Kodak, Agfa/Gevaert and FOMA . Ilford never published their measurements.
    In the case of high acutance, the MTF is higher than 100%, in particular at the lower spatial frequencies. It is often obtained, using adjacency effects in the development process.
    High Definition and high acutance are two different things in the current terminology. Although, sometimes, high defintion has been used for high acutance, 40 years ago. Grant Haist is using that in his book. This terminology leads to some confusion.
    Anyway, I follow the current use of the word. Resolution and sharpness are not in the current vocabulary anymore. Resolution has been replaced by MTF, and sharpness disappeared all together. The MTF description replaced all that.
    I have a Kodak publication of 1976, and at that time already, the developer/film characteristic is given through the MTF representation.

    We often talk about 'compensating developers'. I rather would talk about a developer with a compensating effect, as has been done in the 1930's ( by Hans Windisch). This means an extension of the contrast range in both directions (highlights and shadows). In the past, the extension in the direction of the highlights was very clear. Nowadays with some modern lenses, with good MTF characteristics, the extension into the shadows is very important. This is not just theory. I made photographs to prove this.


    Jed
    Dear Jed,

    I'm sorry, I'm still having difficulty with this. Like 99.9999 per cent of photographers, I can't measure MTF, so I must take another's word for it. On the other hand I can form very good comparative (not merely subjective) judgements on resolution, acutance and grain. These terms may seem outmoded to you, but they have an enormous advantage over MTF: they are usable in the real world of amateur and indeed professional photography. I therefore suggest that my usage is actually the more useful and generally understood.

    There seem to be ever more areas for discussion, such as 'image distortion as small as possible' as applied to developers. There are also distinctions I find odd such as 'compensating developers' and 'developers with a compensating effect," and I really find it very difficult to understand, let alone accept, your assertion about compensating developers having as marked effect in the shadows. This is governed by exposure, speed (which is of course developer related, but nothing to do with compensation) and lens contrast -- or MTF, if you will.

    Compensation is not an extension of the contrast range but rather a compression; an increasing differentiation in the toe and the upper part od the curve. In a sense this is a question of terminology: a compensating developer allows the print to accommodate a greater tonal range without dodging or burning, but it reduces the information carrying capacity of the negative.

    I think that perhaps it is best to terminate this discussion before we confuse ourselves (and probably others) any more than we have already done. This is not to denigrate your approach merely to suggest that sometimes it is easier and better to stick with a simple-but-imperfect analysis (memorably described as 'lies-to-children' because that's how teaching proceeds) than to seek another model, perhaps (though not necessarily) more accurate, but less applicable. I hope you will not take this as an attack; I shall definitely go away and investigate your usages further. But, as I say above, I question the value of MTF in home-grown comparisons, and I am less than convinced by some of your original assertions.

    Cheers,

    R.

  2. #22

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    Quote Originally Posted by Roger Hicks View Post
    Dear Jed,

    I'm sorry, I'm still having difficulty with this. Like 99.9999 per cent of photographers, I can't measure MTF, so I must take another's word for it. On the other hand I can form very good comparative (not merely subjective) judgements on resolution, acutance and grain. These terms may seem outmoded to you, but they have an enormous advantage over MTF: they are usable in the real world of amateur and indeed professional photography. I therefore suggest that my usage is actually the more useful and generally understood.

    There seem to be ever more areas for discussion, such as 'image distortion as small as possible' as applied to developers. There are also distinctions I find odd such as 'compensating developers' and 'developers with a compensating effect," and I really find it very difficult to understand, let alone accept, your assertion about compensating developers having as marked effect in the shadows. This is governed by exposure,
    speed (which is of course developer related, but nothing to do with compensation) and lens contrast -- or MTF, if you will.

    Compensation is not an extension of the contrast range but rather a compression; an increasing differentiation in the toe and the upper part od the curve. In a sense this is a question of terminology: a compensating developer allows the print to accommodate a greater tonal range without dodging or burning, but it reduces the information carrying capacity of the negative.

    I think that perhaps it is best to terminate this discussion before we confuse ourselves (and probably others) any more than we have already done. This is not to denigrate your approach merely to suggest that sometimes it is easier and better to stick with a simple-but-imperfect analysis (memorably described as 'lies-to-children' because that's how teaching proceeds) than to seek another model, perhaps (though not necessarily) more accurate, but less applicable. I hope you will not take this as an attack; I shall definitely go away and investigate your usages further. But, as I say above, I question the value of MTF in home-grown comparisons, and I am less than convinced by some of your original assertions.

    Cheers,

    R.

    Dear Roger:

    The concept of Modulation Transfer Function (MTF) is very common ( 1,410.000 entries at google). The lens manufacturers are all giving MTF data. Part of the amateur film manufacturers are giving those data. Zeiss is selling densitometers to measure MTF for years, other companies came thereafter. In the seventies there were people at Kodak stressing the fact that image quality has to be expressed via MTF, and they gave the MTF data for their films. C.N. Nelson in chapter 19 on Tone reproduction in the classic work 'The theory of the photographic process 4 th ed (1976) indicates that the application of sensitometry is a macro reproduction and has its limitations. Here, we are talking on micro reproduction. In that case the MTF approach plays an important role.

    OK, when you prefer another approach; it is up to you.

    I thought, the discussion might be useful because there does not exist an integrated text on the subject for photography based on modern technology. And with 'integrated' I mean the contribution of lenses, films, developers etc. on the quality of the final image.

    Jed

  3. #23

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    Quote Originally Posted by Jed Freudenthal View Post
    Dear Roger:

    The concept of Modulation Transfer Function (MTF) is very common ( 1,410.000 entries at google).
    Jed
    Yes.

    I just said that like 99.9999% of photographers, I can't do my own MTF tests, but would have to rely on published figures. As by definition these do not exist for every combination of cameras, lenses and film that I am likely to use, this seems to me a compelling argument for adhering to the older criteria (and testing prcedures).

    Cheers,

    R.

  4. #24

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    Quote Originally Posted by Roger Hicks View Post
    Yes.

    I just said that like 99.9999% of photographers, I can't do my own MTF tests, but would have to rely on published figures. As by definition these do not exist for every combination of cameras, lenses and film that I am likely to use, this seems to me a compelling argument for adhering to the older criteria (and testing prcedures).

    Cheers,

    R.
    Dear Roger:
    It is not necessary to do your own MTF tests, but it is important to understand the concept of MTF. In this way you can make your own interpretation of say, the quality of a lens. The selection of the lens for your camera can be done in a way, based on facts. Just to give an example.
    I realize that many photographers are not familiar with the concept of MTF. Just a few days ago, an APUG photographer came to me with the MTF data of the new Xenar for the Rollei to be sold this year. With these data at hand I could tell what kind of image one can expect from that lens. I hope, photographers can read that kind of data in the future. It is a matter of familiarization. Maybe the subject of a workshop or so.

    Jed

  5. #25

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    Now where were we? Oh yes speedincreasing developers
    Cheers
    Søren
    Send from my Electronic Data Management Device using TWOFingerTexting

    Technology distinquishable from magic is insufficiently developed

    Søren Nielsen
    Denmark

  6. #26

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    Quote Originally Posted by David A. Goldfarb View Post
    A speed increasing developer like Acufine or Microphen lets you expose the film at a higher speed than the box setting (i.e., it lets you "underexpose" in camera, but you're not really underexposing, because the speed is really higher), but still retain good shadow detail and normal contrast at the reduced exposure.

    This differs from what people normally call "pushing" (attempting to increase film speed substantially by extending development time), which usually increases density in the highlights while not really improving shadow detail significantly, and film speed is measured in terms of shadow detail.
    Good, there are always people who bring us back to the subject

    And then I go back to the remarks of David Goldfarb (see quotation). David is absolutely right in his observation and remarks. Shadow detail in acufine e.g. has a different origin than shadow detail in a non-compensating developer. The acufine will add shadow detail and will not change the normal contrast. That sounds as straightforward language. [ The MTF story is just to clarify this; but the opposite might be the result; poor teachers ].

    Jed

  7. #27

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    Quote Originally Posted by Jed Freudenthal View Post
    . Shadow detail in acufine e.g. has a different origin than shadow detail in a non-compensating developer. The acufine will add shadow detail and will not change the normal contrast.

    Jed
    Dear Jed,

    Now we're back on track:

    I am sure you know this, but others who read your post may not: ANY speed increasing developer (e.g. Microphen, DD-X) will increase shadow detail at a constant contrast.

    In what sense has the shadow detail in a compensating developer a different origin from shadow detail in a non-compensating developer?

    Cheers,

    R.

  8. #28

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    Quote Originally Posted by Roger Hicks View Post
    Dear Jed,

    Now we're back on track:

    I am sure you know this, but others who read your post may not: ANY speed increasing developer (e.g. Microphen, DD-X) will increase shadow detail at a constant contrast.

    In what sense has the shadow detail in a compensating developer a different origin from shadow detail in a non-compensating developer?

    Cheers,

    R.
    Dear Roger:

    Thanks to our danish friend, we are back on track. B.t.w where is Aquitaine? I am quite often in the Aquitaine in France; but is that where you are?

    Anyway, I will try to clarify why a compensating developer like acufine will show the shadow detail better, without changing the contrast in the middle area. And then in non-scientific language. To that end we have to look at a shadow in the world around us. Or even better, look at the brightness (luminance) distribution in the middle area. You will notice, that the luminance in no spot is really the same as in the spot next to it.
    The brightness is an ever changing in nature, from every spot to every spot.. And, it is the brightness (luminance) that we are recording on our film.
    Now, when you look at the shadows, it is exactly the same as with the middle tones. It is possibly a little more difficult to observe, because it is darker, but there is a variety of brightnesses. Some are tiny, some are only a little brighter or darker than the surroundings. Anyway, a shadow area in nature is not an area of an uniform brightness, but a complex of many brightnesses.
    Now, if you take a developer that can catch this complex picture of different brightnesses, you will get the complete richdom of the shadow in your image. Now, this is what a compensating developer does. Of course, it will add extras in the middle tones too; but this is less noticed.
    With high quality lenses, the effect in the shadows is very pronounced, because tiny lighter spots in the shadows will show up.
    A non compensating developer may have certain qualities, but not the quality to record all those details in the shadows ( and in the middle tones and highlights)

    Jed

  9. #29

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    Quote Originally Posted by Jed Freudenthal View Post
    Dear Roger:

    Thanks to our danish friend, we are back on track. B.t.w where is Aquitaine? I am quite often in the Aquitaine in France; but is that where you are?

    Anyway, I will try to clarify why a compensating developer like acufine will show the shadow detail better, without changing the contrast in the middle area. And then in non-scientific language. To that end we have to look at a shadow in the world around us. Or even better, look at the brightness (luminance) distribution in the middle area. You will notice, that the luminance in no spot is really the same as in the spot next to it.
    The brightness is an ever changing in nature, from every spot to every spot.. And, it is the brightness (luminance) that we are recording on our film.
    Now, when you look at the shadows, it is exactly the same as with the middle tones. It is possibly a little more difficult to observe, because it is darker, but there is a variety of brightnesses. Some are tiny, some are only a little brighter or darker than the surroundings. Anyway, a shadow area in nature is not an area of an uniform brightness, but a complex of many brightnesses.
    Now, if you take a developer that can catch this complex picture of different brightnesses, you will get the complete richdom of the shadow in your image. Now, this is what a compensating developer does. Of course, it will add extras in the middle tones too; but this is less noticed.
    With high quality lenses, the effect in the shadows is very pronounced, because tiny lighter spots in the shadows will show up.
    A non compensating developer may have certain qualities, but not the quality to record all those details in the shadows ( and in the middle tones and highlights)

    Jed
    Dear Jed,

    The very north of the historic Aquitaine; near Thouars, the last city to fall to the French in the Hundred Years' War.

    Either I am misunderstanding you grievously or your explanation of a compensating developer is at variance with the facts.

    Shadow density in any given developer depends on exposure and development time. In order to remove the variable of development time, the original DIN standard specified development to gamma infinity and a fixed density of 0,10; the original Kodak/ASA standard specified a fractional gradient criterion; and the current ISO standard combines the two in a rather ingenious way with the fixed density and a gradient that is near enough 0,615.

    Film speed (= shadow density under the specified contrast criteria) varies with developer. A speed increasing developer such as Ilford DD-X will give a true ISO speed of better than 650 with Ilford HP5 Plus. A fine grain developer may reduce the true speed to 250 or less. This is completely separate from any compensating effect.

    Compensation is a means of allowing development to continue in the shadows while suppressing it in the highlights, by the simple means of exhausting the developer in the highlights. This 'pushes over' the shoulder of the D/log E curve, thereby inevitably compressing the differentiation of the mid-tones: the paper can only represent a log density range of about 2.2 maximum, 1.95 dynamic, so if a longer subject brightness range is represented in that print, the tones must be compressed one way or another.

    There are three main ways of doing this: reduced development, softer paper, and compensating developer. The first two compress all tones more or less evenly; the last compresses the mid tones, thereby allowing better representation of both shadows and highlights, but always at the expense of the mid tones. It cannot be otherwise.

    Let us now consider a big step wedge with widely spaced 1/10 stop gradations. A contrasty lens/camera system -- not necessarily the same thing as a lens with a high MTF at high frequencies -- will have less flare and is more likely to differentiate all the tones in the shadows. With a low-contrast system, flare will 'fill' the shadows, which will be accordingly more poorly rendered.

    Now, perhaps what you are saying is that a compensating developer allows overdevelopment for a steeper toe (and hence better differentiation of closely separated shadow tones) without excessive highlight contrast. This is probably true with the right developer, but I would be astonished if the development in this case met ISO contrast conditions and, as I say, the mid-tones must be compressed, i.e. the curve becomes more S-shaped. Whether or not this is desirable will of course depend on the subject matter and brightness distribution. I would also be surprised, having plotted a number of D/log E curves in my time, if the increase in shadow detail were anything like as significant as the pushing-over of the shoulder.

    A further complication is that increased agitation will raise toe speed at a given contrast (and therefore the ISO speed), while compensating developers necessarily rely on reduced agitation.

    I would therefore argue that first, while a contrasty lens is very highly desirable, the 'relevant frequencies' which you mentioned but never defined can afford to be quite low, corresponding perhaps to 50-60 lp/mm, and second, that except for subject with a very long brightness range, a true speed increasing developer is vastly more useful than a compensating developer.

    I apologize for the excessively long letter, and the somewhat combative tone of the second paragraph, but really, I cannot see your argument. I am not completely ignorant in this field, having started some 40 years ago and numbering among my friends and (more usually) acquaintances a number of people who are very knowledgeable indeed in various photographic fields. They know much more than I, but I must say that in many years of conversation and correspondence I have never been quite so perplexed by the arguments of somone apparently knowledgeable.

    I'll end by straying (slightly) off-topic again, with something which a Zeiss lens designer once said to me: I think it was Dr. Hubert Nasse, but it was a good few years ago, so I'm not sure. It seems to me to cut to the centre of this discussion, and to apply to most of photography. I paraphrase from memory:

    "You can design a lens, and computer-simulate it, and think you know everything about it, but until you build it, you won't know how it performs. And even when you have built it, you can't quantify everything about it. Every lens has its own look..."

    Cheers,

    R.

  10. #30

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    Quote Originally Posted by Roger Hicks View Post
    Dear Jed,

    The very north of the historic Aquitaine; near Thouars, the last city to fall to the French in the Hundred Years' War.

    Either I am misunderstanding you grievously or your explanation of a compensating developer is at variance with the facts.

    Shadow density in any given developer depends on exposure and development time. In order to remove the variable of development time, the original DIN standard specified development to gamma infinity and a fixed density of 0,10; the original Kodak/ASA standard specified a fractional gradient criterion; and the current ISO standard combines the two in a rather ingenious way with the fixed density and a gradient that is near enough 0,615.

    Film speed (= shadow density under the specified contrast criteria) varies with developer. A speed increasing developer such as Ilford DD-X will give a true ISO speed of better than 650 with Ilford HP5 Plus. A fine grain developer may reduce the true speed to 250 or less. This is completely separate from any compensating effect.

    Compensation is a means of allowing development to continue in the shadows while suppressing it in the highlights, by the simple means of exhausting the developer in the highlights. This 'pushes over' the shoulder of the D/log E curve, thereby inevitably compressing the differentiation of the mid-tones: the paper can only represent a log density range of about 2.2 maximum, 1.95 dynamic, so if a longer subject brightness range is represented in that print, the tones must be compressed one way or another.

    There are three main ways of doing this: reduced development, softer paper, and compensating developer. The first two compress all tones more or less evenly; the last compresses the mid tones, thereby allowing better representation of both shadows and highlights, but always at the expense of the mid tones. It cannot be otherwise.

    Let us now consider a big step wedge with widely spaced 1/10 stop gradations. A contrasty lens/camera system -- not necessarily the same thing as a lens with a high MTF at high frequencies -- will have less flare and is more likely to differentiate all the tones in the shadows. With a low-contrast system, flare will 'fill' the shadows, which will be accordingly more poorly rendered.

    Now, perhaps what you are saying is that a compensating developer allows overdevelopment for a steeper toe (and hence better differentiation of closely separated shadow tones) without excessive highlight contrast. This is probably true with the right developer, but I would be astonished if the development in this case met ISO contrast conditions and, as I say, the mid-tones must be compressed, i.e. the curve becomes more S-shaped. Whether or not this is desirable will of course depend on the subject matter and brightness distribution. I would also be surprised, having plotted a number of D/log E curves in my time, if the increase in shadow detail were anything like as significant as the pushing-over of the shoulder.

    A further complication is that increased agitation will raise toe speed at a given contrast (and therefore the ISO speed), while compensating developers necessarily rely on reduced agitation.

    I would therefore argue that first, while a contrasty lens is very highly desirable, the 'relevant frequencies' which you mentioned but never defined can afford to be quite low, corresponding perhaps to 50-60 lp/mm, and second, that except for subject with a very long brightness range, a true speed increasing developer is vastly more useful than a compensating developer.

    I apologize for the excessively long letter, and the somewhat combative tone of the second paragraph, but really, I cannot see your argument. I am not completely ignorant in this field, having started some 40 years ago and numbering among my friends and (more usually) acquaintances a number of people who are very knowledgeable indeed in various photographic fields. They know much more than I, but I must say that in many years of conversation and correspondence I have never been quite so perplexed by the arguments of somone apparently knowledgeable.

    I'll end by straying (slightly) off-topic again, with something which a Zeiss lens designer once said to me: I think it was Dr. Hubert Nasse, but it was a good few years ago, so I'm not sure. It seems to me to cut to the centre of this discussion, and to apply to most of photography. I paraphrase from memory:

    "You can design a lens, and computer-simulate it, and think you know everything about it, but until you build it, you won't know how it performs. And even when you have built it, you can't quantify everything about it. Every lens has its own look..."

    Cheers,

    R.

    Dear Roger,

    Interesting to note, you are living in the French Aquitaine. My brother, and his family are living there too. ( Portets, Bordeaux and Toulouse). So I am in the Aquitaine from time to time. Just two months ago I was there, and I got some wine in my cubitainers.

    Let our first staring point be the remark of David, that it is possible to get better shadow detail using a developer like acufine. And I agree with that. The question is: what is the explanation. My answer is: you cannot explain it in a sensitometric way. THis is a macroreproduction. One cannot apply it to a developer like acufine. Such a developer has a microreproduction. Hans Windisch, in his famous book 'New Photo School' has described already in the 1930 th how to deal with this phenomenon. I would think, this is enough for the average photographer ( certainly for David).
    Another question is the explanation of this phenomenon. And, I think it is very hard to give an explanation without getting involved in scientific matters.
    The best thing is, I would say, try a compensating (or High Definition) developer and look at the result. The result is, what counts. There are quite a number of that kind of developers around. Acufine is a commercially available one, and I have published on the APUG site a few recipes of my own. In the Netherlands, we have made comparisons between the developers in a workshop which was held last fall.

    Jed

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