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  1. #371
    Rudeofus's Avatar
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    From reading previous postings, Mark had excellent reproducibility even when he redid tests on different days, so most likely the error bars will be much smaller than you think. It is cheap and easy to ask for multiple test runs, but expensive and tedious to actually do them.

    With that in mind, I would recommend he repeats tests where he measures anomalies in order to make sure that we don't try to solve a mystery which turns out a measurement artifact. Such a repeat test could also tell us whether the anomaly is consistent or random.
    Trying to be the best of whatever I am, even if what I am is no good.

  2. #372

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    My testing has revealed an odd phenomenon with both XTOL and D316: Large areas that are heavily exposed can develop to a greater density, and nearby thinner areas will develop to a lower density, causing an overall increase in contrast. Here's an example showing a small amount of this:

    Click image for larger version. 

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    Notice that the slope increases slightly after X=1.5. That's where the top row of denser Stouffer wedges starts. This slope-change is not due to uneven lighting because other graphs are straight through there. Here's a more severe example with XTOL:

    Click image for larger version. 

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    This is two Stouffer graphs concatenated together at X=3.0, where the second got much more exposure. The D316 graphs match nicely, but XTOL's graphs have a big jump where density was higher. This density-boost only seems to occur where large areas have much exposure, so maybe nobody cares about it. But I'd like to avoid it in my testing. I'm thinking of shooting a roll where each frame has only a small area of a given exposure. That would eliminate this "overexposed neighbor effect" as I'll call it, and would give me 37 wedges instead of 21.

    Any idea why this occurs? Is this a well known phenomenon?

    Mark Overton
    Last edited by albada; 12-19-2012 at 03:09 PM. Click to view previous post history.

  3. #373

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    Bruce Osgood asked about Delta 100. I'm done testing it, and it works fine in D316. I suggest 13.5 minutes at 20C.

    Delta 100 was interesting because, unlike all other developers I've tested, Ilford evidently did not use the ISO method of determining speed. If they had, the speed would be at least 200 and the darker shadows would be nearly black and indistinct. That's because this film has a long toe, and at the ISO speed point of 0.1 above B+F, the slope of the density-curve is still too low. I've been measuring contrasts using ISO speed points, and got odd results with Delta 100 until I figured out what was going on.

    I've tested all major-brand films in production except Delta 3200 (that will be this weekend), and all work fine in D316. I'll post a long report detailing each film when I finish reviewing results and checking grain and sharpness.

    Mark Overton

  4. #374

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    Strange, I've not found Delta 100 to have a long toe in any developer I've tested it with. In developers including D-76, XTOL and even Perceptol I've found its curve to be nearly identical to that of TMX, with Delta having only a very slightly longer "toe" (and I mean a really small difference), and slightly higher highlight contrast. If developed in DDX, Delta does slightly better on speed and toe contrast than in other developers.

  5. #375

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    Quote Originally Posted by Michael R 1974 View Post
    Strange, I've not found Delta 100 to have a long toe in any developer I've tested it with. In developers including D-76, XTOL and even Perceptol I've found its curve to be nearly identical to that of TMX, with Delta having only a very slightly longer "toe" (and I mean a really small difference), and slightly higher highlight contrast. If developed in DDX, Delta does slightly better on speed and toe contrast than in other developers.
    I rechecked my numbers, and indeed they say that if you use a speed point of .1 over b+f, the speed is well over 100. I interpreted that to mean a longer toe. Here are most of my Delta 100 graphs:

    Click image for larger version. 

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    XTOL is overdeveloped because I used the DigitalTruth time of 8 min instead of Ilford's 7.5 min.

    A side-topic: The two curves for D316 were exposed and developed identically in all respects, including agitation-times of 10 sec each minute. However, I used vigorous agitation for the blue graph and gentle for the green. The vigorous agitation pulled up the shoulder, and had no other effect on the curve. As somebody said, "agitate for the highlights".

    Mark Overton

  6. #376
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    Mark;

    If you slide those curves around a bit, you find that the Xtol causes higher speed and sharper toe. Your developer is softer in the toe then and has low Dmax.

    PE

  7. #377

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    Quote Originally Posted by Photo Engineer View Post
    Mark;
    If you slide those curves around a bit, you find that the Xtol causes higher speed and sharper toe. Your developer is softer in the toe then and has low Dmax.
    PE
    X=0 represents the same exposure for all three. Why shift the curves?
    Also, XTOL is overdeveloped, which gave it a bit of pushing-effect, shortening its toe.

    Mark

  8. #378
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    Mark;

    You shift curves to evaluate their absolute shape minus speed changes. We have a method to do that at EK. We plot each curve on a sheet of paper and then shift them electronically or on a light table mechanically.

    PE

  9. #379
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    SNIP
    Quote Originally Posted by albada View Post
    Delta 100 was interesting because, unlike all other developers I've tested, Ilford evidently did not use the ISO method of determining speed. If they had, the speed would be at least 200 and the darker shadows would be nearly black and indistinct. That's because this film has a long toe, and at the ISO speed point of 0.1 above B+F, the slope of the density-curve is still too low. I've been measuring contrasts using ISO speed points, and got odd results with Delta 100 until I figured out what was going on.


    Mark Overton
    end snip

    I am not a chemist or chemical engineer, I grope my way by trial and error without the aid of sophisticated analysis machines. I have found Delta 100 to perform to my liking by rating it at 125 - 150. Using Kodak produced Xtol my development times are less than 8:00 with Jobo rolling development. I do not pre rinse. I like your findings and hope you will detail the formula's for the Concentrate and D316 in layman's form.

  10. #380

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    Quote Originally Posted by Photo Engineer View Post
    Mark;
    You shift curves to evaluate their absolute shape minus speed changes. We have a method to do that at EK. We plot each curve on a sheet of paper and then shift them electronically or on a light table mechanically.
    PE
    I see what you mean -- you're shifting them horizontally (along X) to remove speed-differences, aligning them with toe-area or linear-area or wherever.

    Since we're on the topic of evaluating density-curves, I was wondering why Kodak chose to put the right end of the "CI ruler" at 2.2. That ruler is marked 0.2 and 2.2, which gives a distance of 2.0 from the speed point. At a normal CI of 0.58, the distance of 2.0 corresponds to an X-axis distance of 1.73 using simple trig:

    Xdist = 2.0*cos(arctan(0.58)) = 1.73

    Converting 1.73 into stops: 1.73/0.3 = 5.75, which means that CI (at .58) assumes the scene contains 5.75 stops of luminance-range. Isn't that too low? I thought scenes contained a larger range than that, around 7 stops. It appears that CI is ignoring some of the highlights. Or did I miss something?

    Mark Overton



 

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