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  1. #211
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    I've added a few things to one of the two quad examples from post #201. This example has it's exposure based on the ISO. Zone V represents the metered exposure. As the example shows, the equation of metered exposure is 8 / ISO and the example uses a 125 speed film so the metered exposure is 0.064 lxs. Speed point falls Δ 1.0 log-H units below at 0.8/ISO or 0.8 / 125 = 0.0064 lxs. So in this example, the exposure was perfect for a film that has an ISO of 125. Zone I falls below the speed point at 0.0041 lxs.

    Attachment 66741
    For something that is impossible that was pretty easy.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  2. #212
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    For something that is impossible that was pretty easy.
    It's a specific example and not universally applicable. Click image for larger version. 

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    Click image for larger version. 

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    Last edited by Stephen Benskin; 04-04-2013 at 12:17 AM. Click to view previous post history.

  3. #213
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    It's a specific example and not universally applicable. Click image for larger version. 

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    Attachment 66747
    I realize that its a special case but only because you are using ISO speed point as the reference point.

    Your example provides an interesting problem for the ISO standard, "how do I get it to describe what my mid-tones will do in a print?" In a simplified sense, it can't, the question the ISO standard and other shadow point methods answer is just "what the reasonable lower limit?" We still have to figure out how the rest of the film behaves.

    If the "print reference point" is the "metering point" and that was simply a density of .4 or .45, something appropriate, we might talk about film characteristics differently. TX might still get a 400 rating and TXP might get 200, so what, .4 may very well be a better predictor of print results.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  4. #214

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    Quote Originally Posted by markbarendt View Post
    Your example provides an interesting problem for the ISO standard, "how do I get it to describe what my mid-tones will do in a print?" In a simplified sense, it can't, the question the ISO standard and other shadow point methods answer is just "what the reasonable lower limit?" We still have to figure out how the rest of the film behaves.
    Not exactly true. The ISO standard has a "triangle" of conditions/parameters to be satisfied in finding the speed point. It specifies a growth in density to 0.8, 4 1/3 stops up from the speed point of 0.1 above B+F. So there is a required gradient up into the midtones. Granted depending on the film and processing the curve over that range may exhibit varying degrees concavity, but by the time you're into the midtones that is pretty much a non-issue.

    In a broader sense, the delta-X method relates the speed point (essentially the basis for shadow point methods) to the fractional gradient method - which was based on print studies, not arbitrary shadow placements.

    My two cents.

  5. #215
    markbarendt's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Not exactly true.
    I do realize that. Still the example provides a pretty stark difference. Wonder how Delta X would change that graph?
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #216
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    I do realize that. Still the example provides a pretty stark difference. Wonder how Delta X would change that graph?
    As the fractional gradient / Delta-X speeds don't change as quickly with development as the fixed density speeds (which aren't supposed to be used beyond the ISO parameters), the overall negative density will tend to increase and decrease in comparison to the fixed density negatives. This is one of the primary arguments against the idea of the just black printing approach for anything other than normally processed negatives.

    How will Delta-X change the example? It wouldn't. The ISO standard uses Delta-X Criterion. That's why the US agreed to the change.

    Apart from the greater tendency of what Jones calls "first choice prints" is more likely under certain printing conditions, I can't see a problem attempting to peg a certain density at a certain point on the curve. As long as the photographer has customized it to their materials and personal preference. A specific target negative density; however, shouldn't be considered universally applicable. Take the two quad example. What makes it a correct exposure for the ISO is not the negative density at the metered exposure point, but that the metered exposure was at 8/ISO and the exposure fell at the correct ratio from the speed point.

    In the scientific photography papers, phrases like "greater tendency" and "more likely" are used a lot. Most methodologies will work adequately. The question is always about the one which has better results most often. This doesn't mean that in certain situations another method will work better. Just that in most situations, one method tends to have a higher consistancy. The question of fixed density vs fractional gradient is about what is more accurate over the greatest number of situations. It's all one big normal distribution curve. Advocating one approach over another is only about what is more likely.
    Last edited by Stephen Benskin; 04-04-2013 at 01:01 PM. Click to view previous post history.

  7. #217
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    Hi Guys,

    I have repeat the ISO Test with a Gray Card... Photographing with a 400 TX I have to setup the Lightmeter to ISO 200 for my personal setting ;-)
    Everything is good:-)

    THX for your great constructive help!
    It´s time to take pictures :-)

  8. #218
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    Is there a prefered way how the development times should be changed? I would like to retest FP4+ in 510-pyro semi-stand developed. My current development time is 18 minutes. So I was thinking to use 5 developments of resp. 5.5, 8, 11, 19 and 22 minutes. Any ideas why this is a good or bad idea?

  9. #219
    Rafal Lukawiecki's Avatar
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    I'd make the longest time a bit longer, so if you wish to have 19 min, make the longer one, perhaps 35 min. The idea is not to hit the exact target time with a test, but to generate enough data to the "right" and "left" of your target times that let you safely interpolate the actual, correct duration. If you feel that you are good with 18 min, and you wish to re-test, then you need enough data on both sides of the 18 min to be sure that, for example, 25 would not be better.

    In general, choosing 5 dev times that follow the sqrt(2), ie, 1.4142 sequence helps to cover enough range for typical N-2 to N+2 needs. If your 18 min seems to be your N time, then I'd suggest a sequence of: 9, 12, 18, 25, 36 min. The key to the test is the interpolation of the correct times in-between the tested ones, based on the curves/contrasts that you would get from those tests, and those that you would desire to get. Ralph's method will lead you there, or you could follow many others. I've published curve-plotting software on this forum, too, which can also calculate the resulting times, based on your contrast requirements, but it can all be done, easily, by hand.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles



 

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