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  1. #91
    Bill Burk's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    ... N-2 development, that, unless I give substantially more exposure (along the lines of that suggested by the fixed-point speed) to compensate for the reduced development, my shadow values suffer.
    Hi Doremus,

    When you use N-2 to accommodate a long scale subject, your aim is still to print on Grade 2 paper. The shadows are suffering not for lack of any detail, but for lacking enough detail to be revealed on Grade 2 paper. So increasing exposure is a good idea for this case.

    The Delta-X criterion justifies using the same speed according to the fractional gradient method, for a relatively normal scene where the underdevelopment is done for other purposes, say... to maintain high resolution and fine grain. Then the aim would be to print on Grade 4 paper, and the speed could be same and give a similar print as a normally developed negative of the same scene printed on Grade 2.

  2. #92
    Stephen Benskin's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    I mentioned earlier a disconnect (for me, anyway) between ISO and personal E.I. But, if I accept that, then it would seem that much of the exposure compensation that I have been doing for expansions and contractions would be unnecessary. This confuses me a bit, for it really seems to me that when I make a negative of a very contrasty scene that requires, say, N-2 development, that, unless I give substantially more exposure (along the lines of that suggested by the fixed-point speed) to compensate for the reduced development, my shadow values suffer. Conversely, expansion negatives are often overexposed (which doesn't bother me much) if I don't compensate by reducing exposure.

    This is the disconnect I am addressing. And, I don't even really know where to start asking informed questions about it except to fire away and hope you will indulge me yet again. So, did the first excellent print tests include lots of expansion and contraction subjects, or were they more or less concerned with prints of subjects with more "normal" SBRs? If so, then should we expect much different results for similar print tests with subjects with significantly higher or lower SBRs? If not, then why does it seem that in practice I have to compensate exposure for contractions and expansions than the Delta X or fractional gradient speeds would suggest?
    Since the effective film speed is based on 0.3x average gradient, you shouldn't expect to match the over all density of negatives with expansion and contraction development to that of a normal negative. The overall negative density will change with development, but the shadow gradient at the speed point remains at 0.3x average gradient (this is why the just black proof is valid only with normal development). Things tend to get more complicated at the extremes. The degree of flare is more of an uncertainty, as is preferred tone reproduction. We haven't even discussed developmental models yet. I'd like to show you a four quadrant example, but my program is down because of a conflict with Internet Explorer and I don't have an example of a N-2 development. I have one of a large subject luminance range with 2 stops flare and compensation with the paper grade, but that might just muddy the waters. Anecdotally, when I shoot scenes that I intend on progressing less than -1, I tend to error on the safe side.

    One of my favorite Jones quotes comes from A Study of Various Sensitometric Criteria of Negative Film Speeds. This is the paper comparing various speed methods to the print judgement speeds. Jones writes, "From the standpoint of tone reproduction theory there seems to be no justification for the adoption of any value of density as a significant criterion of the speed of a photographic negative material. The primary function of the negative material is to record brightness differences existing in a scene. Density, per se, has no significance as an indication of the ability of the photographic material to perform this function. The value of negative density by which any particular object brightness is rendered, as, for instance, the deepest shadow, is of no consequence except insofar as it may have some bearing on the exposure time required to make a print from a negative.

    Tone reproduction theory indicates that there is only one characteristic of the negative curve that is significant in expressing the capacity of the material to reproduce brightness (luminance) differences, and it is upon the way in which brightness differences are reproduced that the quality of the film positive must depend. This characteristic of the D-log E relationship to the gradient or slope, since this determines the magnitude of the density differences by which brightness differences in the object will be rendered in the negative and eventually in the positive made therefrom."

    More specifically, I do have a development chart that uses both fixed density and Delta-X speed determination. In this example, I used a fixed flare model to determine aim contrast index. Fixed flare tends to higher and lower CIs faster as the luminance range moves out from the statistical normal then variable flare.

    Click image for larger version. 

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    For a reference, here is a data from one of the images used in the first excellent print test.

    Click image for larger version. 

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    To answer your question about terminology. EI or effective film speed seems to be commonly used for any method of determining speed outside of the ISO standard. I prefer effective film speed for sensitometrically tested film because EI has other uses.

  3. #93
    Stephen Benskin's Avatar
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    What's important to remember about speed points is that they don't necessarily represent where the exposure is supposed to fall. For the fractional gradient point, it is the 0.3x average gradient point and can be considered the minimum useful gradient point. The Delta-X criterion's and the ISO standard's use of the 0.10 fixed density point is in it's correlation to the fractional gradient point. The testing establishes the lower limitations of the film. Based on this point, any adjustment would be relative to this known quality limitation. Once the speed point is determined, the exposure required to produce that point is entered into an equation that contains a speed constant. The film speed value is part of the exposure meter's equation to determine exposure placement. There is a known relationship between the exposure at the speed point and the exposure at the metered exposure point. Adjusting the speed constant, changes the film speed and consequently changes the relationship between the speed point and the metered exposure point.

    The speed equation for reversal film used to be 8 / HR, which is the metered exposure point. Now itís 10 / HR. Thatís a 1/3 stop adjustment without changing how the speed point is determined. The same could have been said for b&w film speed. They could have simply adjusted the film speed constant to eliminate the safety factor, but many people didnít like how difficult it was to determine the fractional gradient speed point. The only way to create a universal standard was to simplify the process. Thatís where Delta-X comes in. It has good correlation with the fractional gradient method while using an easy to find fixed density.

    Hereís an example of the math. This is all built into the ISO standard when the ΔD is 0.80 at Δ 1.30 log-H, but if you want effective film speeds for any other development conditions, youíll need to use the equations. Anyone recognize the ISO standard's contrast parameters in this example?

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    This chart gives the ΔX value for a given ΔD.

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  4. #94
    Stephen Benskin's Avatar
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    The value of Delta-X is the difference between the fixed density point of 0.10 and the fractional gradient point which is the speed point. Referring to the Delta-X Table in the previous post, as the contrast (ΔD) is reduced, the value of ΔX increases and as the contrast is increased, the value of ΔX is decreased. The further to the left of the speed point, the faster the film is in relation to what it would be using only the fixed density method. What this means is that the film doesn't lose speed as quickly with reduced development and doesn't increase as significantly with expanded development compared to the fixed density method. With the Delta-X method, the speed point will remain at the same 0.3x average gradient at all levels of processing. It's an apples to apples comparison.

  5. #95

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    This is a great, informative thread. I've read it and reread it a couple of times to try and follow it all. Now please bear in mind I'm not very well versed in the development procedures. That said, have I got the (admittedly oversimplified) generalizations correct?

    1) E.I. is a personal choice based upon how the developed images correlate with the desired intent of the photographer whereas the ISO is the standard given as a starting reference by the manucaturer.

    2) The photographer sets the film speed on the camera *at the ISO* and develops as though it were shot *at the E.I.*

    Knowing that the E.I. is a personal choice of the photographer, for those of you who have gone through the process of determining your own E.I., may I ask what specific criteria you found useful in this process? At what point in your photography did you feel you'd learned enough to evaluate those criteria?

    Thanks!

    John

  6. #96
    markbarendt's Avatar
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    John, three criteria.

    Can I get the print I want?

    How easy is it to get that print?

    How big is my safety factor? (How far can I over or under expose and get what I want?)

  7. #97
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    Quote Originally Posted by pharmboycu View Post

    Knowing that the E.I. is a personal choice of the photographer, for those of you who have gone through the process of determining your own E.I., may I ask what specific criteria you found useful in this process? At what point in your photography did you feel you'd learned enough to evaluate those criteria?

    Thanks!

    John
    The work of Jones et al provides me with a good minimum point for the EI and I have no qualms his findings. I found the "W speed" as an estimation of 0.3G easier to calculate with a spreadsheet than either directly finding 0.3G or claculating Delta-X. So I use that [W-speed] when I do the math on my sensitometric data.

    To link my sensitometric findings with a lens/shutter/camera/exposure meter system I use the 0.1log d ASA method with an 'in camera' Zone 1 exposure.

    I also, have been using a 'minimum flare density of 0.1 log d' by placing a box or can with a hole in it in a typical composition. This provides a simple and practacle empiric solution to the issue of flare and its effect on film speed.

    For my large format work I tend to use a generous safety factor to minimize exposure errors in the field. This is possible because there is very little or no image deterioration of the 8x10 negative image due to over exposure. Especially when considering the largest prints I make with that format are only 2.4x magnification ( 20x24").

    I control contrast when I print (dichroic head) so that simplifies negative processing a thousand-fold
    Last edited by ic-racer; 05-08-2014 at 08:30 AM. Click to view previous post history.

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