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  1. #21
    Stephen Benskin's Avatar
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    Quote Originally Posted by CPorter View Post
    Not much difference there.....the off set is due to the sheet's formulas being set up for a NDR of 1.2, your suggestion was an NDR of 1.1. Maybe Ralph will chime in on it soon.
    That's interesting. Thanks for taking the time to do that. I decided to plug your numbers into my program. I got values very close to those Bill got with his hand drawn curves and CI overlay.

    Results from my program:

    4 min 0.41
    5.5 min 0.44
    8 min 0.50
    11 min 0.57
    16 min 0.68

    My program uses a variation of contrast index where it uses 0.10 as a base and draws an arc 2.0 log-H units to the right. As described in Photographic Materials and Processes. Just to help illustrate the how the various methods of measurement can effect the results, my program also does Ilford's G bar with a log-H range of 1.50 and an average gradient with a log-H of 1.80. I got 0.72 for the 1.80 average gradient method.

    And here's a Time/CI Graph. As you can see, it's smoother than the one derived from the values from Ralph's spreadsheet, which is a positive indication as to the validity of the results.

    Click image for larger version. 

Name:	Time gradient Curve - Chucks data - My program.jpg 
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    Last edited by Stephen Benskin; 06-16-2012 at 09:36 PM. Click to view previous post history.

  2. #22
    CPorter's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    That's interesting. Thanks for taking the time to do that. I decided to plug your numbers into my program. I got values very close to those Bill got with his hand drawn curves and CI overlay.

    Results from my program:

    4 min 0.41
    5.5 min 0.44
    8 min 0.50
    11 min 0.57
    16 min 0.68

    My program uses a variation of contrast index where it uses 0.10 as a base and draws an arc 2.0 log-H units to the right. As described in Photographic Materials and Processes. Just to help illustrate the how the various methods of measurement can effect the results, my program also does Ilford's G bar with a log-H range of 1.50 and an average gradient with a log-H of 1.80. I got 0.72 for the 1.80 average gradient method.

    And here's a Time/CI Graph. As you can see, it's smoother than the one derived from the values from Ralph's spreadsheet, which is a positive indication as to the validity of the results.

    Click image for larger version. 

Name:	Time gradient Curve - Chucks data - My program.jpg 
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ID:	52570
    That's good to know too, though I have a difficult time believing that the "N" dev times are right, it's because I think I did something wrong, not due to the spreadsheet---so, while I'm waiting for Ralph to have a say on why the results are what they are, I welcome others. I just can't believe that 4 minutes of development is almost "N"!! That would make -1 or -2 rediculously short IMO. For the life of me I can't see what aspect of my process could be the reason for this test showing these results. I lean toward the tablet getting too much exposure, but IDK. I exposed the tablet the way I do for all my other previous testing via Shaeffer. Perhaps that does not work well with Ralph's spreadsheet, IDK.
    Last edited by CPorter; 06-17-2012 at 11:11 AM. Click to view previous post history.

  3. #23
    Bill Burk's Avatar
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    I have a very important observation to make here.

    Because of the long toe and upswept highlights in the curve family from your HC-110 and Tri-X test, it is very important to your prints where you place your shadow exposures.

    The lower on the toe that you place your exposure, the less likely you are going to get chalky highlights. (So do what Ansel Adams would do, not what Bruce Barnhaum would do).

  4. #24
    Stephen Benskin's Avatar
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    I don't know if the spreadsheet plots the film curves in sufficient detail to do this, but one way to check if the gradient values are accurate is to make some mathematically derived density range projections and see if they match up with the actual curves.

    All you need is the Rise / Run = Gradient equation. To determine the density range of any given log-H range, you take the gradient from the spreadsheet and multiply it by a desired log-H range.

    For example:

    5.5 min test
    Gradient: 0.57
    log-H range: 2.10

    Gradient * Run = Rise
    0.57 * 2.10 = 1.20

    or you can use NDR / Gradient = log-H range
    1.20 / 0.57 = 1.20

    May I suggest testing both 0.10 and 0.19 as the base for the log-H range. Don't expect it to be a perfect fit. Curve shape will have an effect, but this should give you an idea if there is a problem with the gradient values or not.

    Here's an example with one of my own tests. I use a NDR of 1.05 and for normal a luminance range of 2.20 with 0.40 flare for an aim log-H range of 1.80. With a film developed to a CI of 0.58 the NDR of 1.05 should be achieved at a log-H range of 1.81.

    Click image for larger version. 

Name:	NDR check from projection.jpg 
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    Just for the sake of clarity, there is no definitive set of gradient values for the different stages of development. Not only is there the choice of diffusion or condenser enlarger, but the choice of paper (including alternative methods), personal taste for the NDR, what is considered the average luminance range, and flare also play there part. The following example illustrates the results from four different models for diffusion enlargers. While three of the four results are very similar, they are determined using different variables. The Practical Flare Model is mine and is determined using a combination of a fix flare and variable flare approach.

    Click image for larger version. 

Name:	CI Development Model Comparison.jpg 
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    Last edited by Stephen Benskin; 06-17-2012 at 03:52 PM. Click to view previous post history.

  5. #25
    RalphLambrecht's Avatar
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    not surprisingly,i get the same results as steve when i work my spreadsheet with the op's data!all is good congrats to an obviously successful test!
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  6. #26
    CPorter's Avatar
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    According to the sheet, N-1 is not obtainable and technically, according to the sheet, neither is N+2. Really? You have no insight as to why -1, not to mention -2, is not possible with this data? For +2, looks like the graph could carry out to 17 min, but that same logic can't be used for -2. This is not acceptable. To proceed from here with these results would be quite a limitation IMHO, does anybody disagree? There has to be a reason for such a limitation on the available SBR's that are being shown possible with this data. The curves graph a perfect match with the Excel file I made for myself to input the data for my previous testing, at least the spreadsheet helps me to confirm that.

  7. #27
    Bill Burk's Avatar
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    Hi Chuck,

    What density range do you want your negatives to have? I used 1.05 for my analysis because it matches Grade 2.

    Your curve family yields a clear Time/CI curve. When I drew triangles on the N-series using the "Contrast Index Required to Print Scenes..." chart, I came up with this absurd series of times.

    *Absurd Series*
    N-3...4:30
    N-2...7:45
    N-1...8:45
    N...11:45
    N+1...about 20:00

    Then.. I took your 11 minute time for N because CI 0.6 is very close to 0.62, and the "Contrast Index Meter" transparent overlay arc crosses very closely to the reasonable negative density. (In other words, CI looks like a good fit for N).

    Then I moved to the left and right increments of 0.30 (one stop). This is where I marked whole N numbers. I plotted these and drew a curve and found the following series...

    *Reasonable Series*
    N-3...2:30
    N-2...4:45
    N-1...7:45
    N...11:00 - benchmark
    N+1... about 20:00

    I believe the main differences in my two methods is that CI does not predict well where the 1.05 negative density is going to be reached... But the curve family nails it! So I am more inclined to trust the series of times that came from studying the curve family and where the highlights will fall.

    Either way you can see N+1 might be 20 minutes or more. If you need to achieve N+1 you should probably plan to use a stronger working dilution of HC-110.
    Last edited by Bill Burk; 06-18-2012 at 08:59 PM. Click to view previous post history.

  8. #28
    Stephen Benskin's Avatar
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    Chuck, if Ralph's results are similar to mine, something isn't right about the results from your test. Somehow it's not interpreting the data correctly. Ralph got different results than you using the same program and your data, and I got similar results to Ralph using a different program.

    If you accept the results I got from your data, your developmental range is from under +2 to +1 with a projected +2 at around 18.5 minutes. Your normal is at 11 minutes. Your testing appears to be successful. I agree here with Ralph. Your testing data is valid. You are standing on solid ground, but you are using a new tool and it's your results that are suspect. Maybe Ralph can suggest what's causing the difference with your results.

    Here are the projected development times based on Ralph's developmental model which is based on a desired NDR of 1.20, an average luminance range of 2.10, and no flare. See the table in post #24.

    Click image for larger version. 

Name:	CI Time Curve - Chuck with development projections.jpg 
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    Last edited by Stephen Benskin; 06-19-2012 at 12:44 AM. Click to view previous post history.

  9. #29
    Bill Burk's Avatar
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    Chuck pm'd me he wants negatives to hit 1.2, and he'd prefer not to include adjustment for camera flare.

    So (same curve family - it is totally valid and remains unchanged) here is a graph showing N-times based on what would hit 1.2 densities in the highlights.

    I was looking at this being "N"...

    Zone VIII = step 5
    Zone I = step 19

    Then I went left and right two steps per stop... Just working to keep the negative to hit 1.2 above whatever Zone I was giving... Not dealing with Contrast Index, just trying to hit the negative densities that Chuck wants versus the exposure the neg has... Just reading off the curve family graph.

    CPorter HC-110 TRI-X v2

    This gives what I believe is reasonable N-Series, but is an unusual method of computation, so I would not be surprised there are other suggested time series that fit the same data...

    N-Times to hit 1.2 negative density in the highlights Zone VIII
    N-2...4 min
    N-1...6:15
    N...9:15
    N+1...13:15
    N+2...about 20 min (recommend stronger concentration of HC-110 to hit this).

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