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Thread: BTZS

  1. #1

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    BTZS

    Do alt printers, using BTZS tests, use 90% for IDmax for their ES (exposure scale) calulation? I was thinking: versus silver gelatin papers, I should try 95 or 100%.

  2. #2

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    Quote Originally Posted by philsweeney
    Do alt printers, using BTZS tests, use 90% for IDmax for their ES (exposure scale) calulation? I was thinking: versus silver gelatin papers, I should try 95 or 100%.
    I use 90%, exactly as Phil recommends. As Arentz writes, all you need are convincing blacks.

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    Quote Originally Posted by philsweeney
    Do alt printers, using BTZS tests, use 90% for IDmax for their ES (exposure scale) calulation? I was thinking: versus silver gelatin papers, I should try 95 or 100%.
    It depends. For carbon printing I use about 95%. For kallitype and Pt./PD. work, the lack of separation in the shadows could justify a figure of as low as 80-85%.

    Sandy

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    Sandy and Jorge: I need a little more help. All pyro negatives are measured in blue channel mode. Although I believe it could be done in visual mode also, resulting in a lower number of units. I believe the blue channel mode increases accuracy and if I had a UV mode even greater accuracy. I did do a PSP test with D76 and delta 100. I did the test twice to verify repeatability. For ES I have taken one of my test negatives (for example a WD2D test negative from the film tests not the stouffer test tablet) and contact printed to my paper. I'll call the test negative the "stained tablet." My premise is the stained tablet will give the correct ES for a WD2D negative to print to my selected paper, etc. To do this I used the WD2D stained tablet as the step tablet in plotter for the paper tests. Does this seem correct for dealing with the pyro negative for use in BTZS? Using IDmax% = 90% I have an ES of 1.27 from a WD2D negative obtained via the described tests for printing to strathmore 400 watercolor kallitype using 4 ml dichromate.

    Some cursory tests with AZO grade 2 and the same premises resulted (IDmax% = 90%): ES scale for stouffer tablet 1.36; WD2D negative, 1.19; pyrocat (1-1-100), 1.02. These results seem to indicate pyrocat gives more effective printing negative densities.

    Compared to D76 negatives my film tests with pyro negatives (pyrocat, and WD2D) result in speed curves that are "zig-zaggy" whereas the D76 speed chart curve is a smoother curve. The pyrocat 1-1-100 chart is particulary questionable. Is this one of the other problems associated with pyro negatives and BTZS?

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    Phil, let me start from your last paragraph. What you mention might be a possibility and one of the objections Phil Davis has, having said that, I have not seen this problem in my tests, and I have seen some curves done by Sandy where his curves are also smooth. You need to remember Pyrocat is a proportional staining developer so your developing technique, agitation etc, might have something to do with this problem.

    I never saw the point of using a "stained" step tablet. My thinking is that even if you read them with the blue channel the total density remains the same. I did an experiment to verify this, I read the stouffers step tablet with a blue channel, with a visible channel and with a UV channel and the values were off only by 0.03. I know Herbst likes to do it this way, me I dont see the point. What we are interested to see is total density, what does it matter if it comes from silver or a combination silver/stain.

    If you are using the win plotter, you can adjust the points somewhat to smooth the curve and give you more reasonable results, I had one instance where I saw that the middle SBR curve had greater speed than the low SBR...clearly this did not make sense, so I adjusted the toe of the curve, only a couple of points and voilà .....

    Ok, sorry for the long windedness, to answer your questions, no, there is no way to extrapolate visible readings to blue readings or UV readings, many people have tried including Arentz and none have been able to come up with a reliable formula. If you plan to use Pyrocat, you really need UV readings for alt printing. Pyrocat can absorb as much as 1 and 1/2 stop more UV than a non staining developer and as much as a stop more than a pyro negative. If you are using the win plotter you can send me your files and I will be glad to take a look at them, also if you want to wait, you can mail me your step tablets, I can read them with the UV channel and make you a win plotter file.
    Your reflection densities of 1.27 seem about right for kallitype so you seem to be on the right path.

  6. #6

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    Jorge, sounds like I really need the UV readings! So if I have the UV readings I would then just use the ES obtained from printing the stouffer tablet to my selected paper? And what about AZO: should I use the 1.36 ES (from my previous post) and use my blue channel negative readings or can UV readings of those be helpful also (since AZO has some UV sensitivity)?

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    Quote Originally Posted by philsweeney
    Jorge, sounds like I really need the UV readings! So if I have the UV readings I would then just use the ES obtained from printing the stouffer tablet to my selected paper? And what about AZO: should I use the 1.36 ES (from my previous post) and use my blue channel negative readings or can UV readings of those be helpful also (since AZO has some UV sensitivity)?
    Yes, if you have UV readings you can use the ES obtained from stouffers, if you dont then using the "stained" step tablet is better as it simulates the UV response.

    On azo, your light source is not an UV source, so I dont see any advantage of using UV readings for them. Although azo is UV sensitive you are not projecting any UV rays with a 300 watt bulb, so who cares, just use your normal ES obtained from the stouffers and the paper.

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    Quote Originally Posted by philsweeney
    All pyro negatives are measured in blue channel mode. .... I believe the blue channel mode increases accuracy and if I had a UV mode even greater accuracy.

    Some cursory tests with AZO grade 2 and the same premises resulted (IDmax% = 90%): ES scale for stouffer tablet 1.36; WD2D negative, 1.19; pyrocat (1-1-100), 1.02. These results seem to indicate pyrocat gives more effective printing negative densities.

    Compared to D76 negatives my film tests with pyro negatives (pyrocat, and WD2D) result in speed curves that are "zig-zaggy" whereas the D76 speed chart curve is a smoother curve. The pyrocat 1-1-100 chart is particularly questionable. Is this one of the other problems associated with pyro negatives and BTZS?


    Phil,

    You can use BTZS testing with great accuracy if you read your stained negatives with a UV densitometry. Blue reading will be off (low) by as much as log 0.50 in the highlights compared to UV reading.

    The brown stain of Pyrocat-HD negatives provides much more actinic filtration of UV light than the stain of WD2D or other pyrogallol based developers. I compared the effect of stain of different developers and you can see the results at http://unblinkingeye.com/Articles/PCat/PCat3/pcat3.html. Just look at the charts near the end of this page. This is the main reason why Pyrocat-HD is so superior to the other pyro staining developers as a dual purpose negative for people who want to print with the same negative on both regular silver papers and in Pt/Pd. This is not true for AZO, however, as the high density range (as measured for blue light) required for printing with AZO results in a negative with UV density range that is much too high for Pt/Pd, though it might work with kallitype or straight palladium.

    I have not experienced any zig-zaggy results in curve data with either Pyrocat-HD or any of the pyro staining developers. If you are getting any it may be a result of the light source producing more fall-off of UV light in certain parts of the circle of illumination than in others. I would suggest increasing the circle of illumination of the light on the baseboard to at a diameter of at least three times the width of the film being tested, and then using only the very center of this circle.

    Sandy

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    roy
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    Unless I am missing something here, does this mean that by not using a UV reading densitometer, the assessment of pyro developed negatives is going to be a bit of a "hit and miss" affair ? Or, conversely,can non-pyro developed negatives be assessed more accurately ?
    Roy Groombridge.

    Cogito, ergo sum.
    (Descartes)

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    Quote Originally Posted by roy
    Unless I am missing something here, does this mean that by not using a UV reading densitometer, the assessment of pyro developed negatives is going to be a bit of a "hit and miss" affair ? Or, conversely,can non-pyro developed negatives be assessed more accurately ?
    If you plan on doing alt processes sensitive to UV only, then yes...if not, then the blue channel will work.

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