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  1. #41
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Variable contrast paper basically has two emulsions, a low contrast layer sensitive to green light, and a high contrast layer sensitive to blue light. When light hits the paper, the more blue there is in the light relative to green, the more the paper's high contrast emulsion is exposed relative to the low contrast emulsion. This produces a higher contrast image. The reverse is true when there is more green light relative to blue light.
    Michael, while I follow your statement, I wonder if you would agree that there is a more detailed explanation of how VC papers work? I would humbly observe that it seems, based on their characteristic curves, that the component emulsions are differently sensitised to the blue and green light and that it is their additive result that creates the actual, observed contrast. Further, modern VC papers, like Ilford (or like Polymax used to) seem to have three emulsions, with the third one being sensitive to both green and blue.

    Unfortunately, this can also lead to some odd behaviours at extreme low grades, such as 00. See Nicholas Lindan short paper: "The Workings of Variable Contrast Papers and Local Gamma". For that reason, split-grade technique can be a little easier to use with filters a little harder, such as 1 and 5, rather than 00 and 5. I believe that is what Bob Carnie practices. The effect will be the same, but the observed changes will seem more logical when using 1 rather than 00 for certain mid-tones.
    Rafal Lukawiecki
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  2. #42
    Steve Smith's Avatar
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    Quote Originally Posted by Rafal Lukawiecki View Post
    modern VC papers, like Ilford (or like Polymax used to) seem to have three emulsions, with the third one being sensitive to both green and blue.
    According to Ilford's data sheet, all of their emulsion layers are sensitive to blue with varying sensitivities to green added.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  3. #43

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    Quote Originally Posted by Rafal Lukawiecki View Post
    Unfortunately, this can also lead to some odd behaviours at extreme low grades, such as 00. See Nicholas Lindan short paper: "The Workings of Variable Contrast Papers and Local Gamma". For that reason, split-grade technique can be a little easier to use with filters a little harder, such as 1 and 5, rather than 00 and 5. I believe that is what Bob Carnie practices. The effect will be the same, but the observed changes will seem more logical when using 1 rather than 00 for certain mid-tones.
    I wonder if this demonstates a difference between the subtractive system of using white light and the additive system of a Blue/Green system.
    Otherwise I have a hard time understanding how using a 1 setting of this much green and this much blue (plus this much blue for the #5 exposure) is different from this much green and (this much blue plus this much blue for the #5 exposure). Moving the brackets does not change the total quantity of green and blue. Comments?
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

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    Bill

  4. #44
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by cowanw View Post
    I wonder if this demonstates a difference between the subtractive system of using white light and the additive system of a Blue/Green system.
    Otherwise I have a hard time understanding how using a 1 setting of this much green and this much blue (plus this much blue for the #5 exposure) is different from this much green and (this much blue plus this much blue for the #5 exposure). Moving the brackets does not change the total quantity of green and blue. Comments?
    Cowanw, I believe there is no difference in the final result, whether you use 00 or 1, with a 4 or a 5, when split-printing, except for the inability to reach the extreme grade of 00 or 5 if those filters are not used. The difference, however, is in the seemingly illogical relationship of the midtones affected by the discontinuity in the emulsion overlap, and the remaining tones, when moving from grade 00 to 0 and onwards. To put it in other words, as you move up a grade, from 00 to 0, and then towards 1, some midtones will immediately print denser at 00, than they would at 0, before they resume their march towards increased density at higher grades. I think this is what leads to a "solarised" look, that Bob Carnie mentioned when describing his 00 experience, see post 43 of this LFPP thread. You can see this in the two jumps of the 00 and 0 grade curves, which I have, rather poorly, plotted below—disregard my error of a non-speed matched system, which lead to the curves not intersecting, as they should, at 0.60 logD. Notice the overall shape, and those almost 1 f/stop jumps, of the 00 curve:

    Click image for larger version. 

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    Quote Originally Posted by Steve Smith View Post
    According to Ilford's data sheet, all of their emulsion layers are sensitive to blue with varying sensitivities to green added.
    Thank you, Steve, for correcting me.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  5. #45

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    Yes, I have followed these threads and seen these graphs. I think they are based on white light and the subtractive system.
    I am wondering if there is a distinction to be made that the definition of grade in the subtractive system is what you get with the provided numbered filter, and with regard to those discontinuities, the filter is not, in fact, correct for that paper at that desired grade. There is, after all, a set of yellow/magenta settings (i.e. colour head) that will give a smooth curve, just not with preset filters
    The blue green system however forces you to find your grade by using the settngs on the enlarger with respect to the paper you are using. Again a smooth curve can be created with the appropriate settings.
    Bob describes solarization or muddiness in the shadows. Other discrepancies are seen at midtone. I am not sure the two observations are related.
    I think Bob's observations need more investigation for an understanding of what he is describing.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  6. #46
    Bob Carnie's Avatar
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    I do not use the 0 and 5 method, not for at least 4-5 years for the reasons Rafal points out. I noticed this visually apparently Nicholas Linden has backed this up with sensitometry, which btw is not my strong suit. I use it for calibrating processes and then move on to my eyes.

    It should be pointed out I am a big time fan of Ilford Warmtone, and now Art 300 which I believe is the same emulsion.... All my comments are directed at this paper .

    I have printed now in two eras... 1 era where there were only graded papers... 2 era where we have Ilford Warmtone ...

    I switched to this paper for a specific reason... my clients liked the prints better...


    Era 1 I remember the days of two bath dev, hot dev tray off to the side to help in the burning in... if you wanted an overall strong contrast print you would move up to a grade three or four and suffer the crazy amount of burning in the highlights.. which after time just got soft and flat/muddy due to the silly burn time, not to mention the fact that the burns could become obvious.

    Era 2 I lay down an initial tone which puts inertia in the highlights and defines a long tonality print.. I then use the grade 5 filter to increase Dmax and contrast to taste.
    I will burn the highlights with low filter and 5 filter, usually this burn is very insignificant and does not soften/muddy up and the blacks within the highlights are more defined and create the illusion of tonality.

    I prefer Era 2 printing which is this controlled mix of filters..
    I use an 80% density rule for the first filter .. in other words I make sure that I am 80 % happy with the density of the upper highlight region and I dodge the shadow regions to make a pleasing print... softer but nice ... think Jock Sturge's print a bit light , a bit soft, but nice blacks starting to emerge.

    Then with a second filter 5 I hit the timer either once , twice or even more to determine the overall final look ..

    During both filter exposures I am dodging to control local areas.

    I use the 00 and 5 for burning in areas that I want to make sure are in the print for aesthetic reasons. I do not like paper white within my images but prefer to see the easal blades lines as a guide for blank sky tonality... If I do not see the separation then I know I need more tone.

    WHAT METHOD AM I USING as I do not like the 0 and 5 method, and I do not like the single filter method...

    Until someone can give it a name I will call it a MODIFIED FILTER METHOD... using the outflanking method to determine initial exposure... and 0 and 5 burning in for aesthetic reasons.

    Its no wonder the OP is getting confused,,, the cat is looking better each day btw,, To be fair to both camps , the image supplied would work in Era 1 or Era 2 with not too much issue.

    I just use the MFM method now for all printing as it gets easier over time.

  7. #47

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    Pleased to see you are following the thread, Bob.
    I like the MFM and particularily the outflanking bit and use that for my 35mm and 4x5 enlargers.
    When I got my 8x10 enlarger I was forced to the 00 and 5 blue/green printing technique and I find it hard to understand and reconcile the common principles.
    Still as you point out, the print is the important thing and how anyone gets there is as valid as the next.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  8. #48
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by cowanw View Post
    Yes, I have followed these threads and seen these graphs. I think they are based on white light and the subtractive system.
    I am wondering if there is a distinction to be made that the definition of grade in the subtractive system is what you get with the provided numbered filter, and with regard to those discontinuities, the filter is not, in fact, correct for that paper at that desired grade. There is, after all, a set of yellow/magenta settings (i.e. colour head) that will give a smooth curve, just not with preset filters.
    Cowanw, you ask an important question. My understanding of the workings of the VC papers, especially Ilford ones, and very much MGIV WT, which similar to Bob, I like very much, is that it should not make any difference, whether you use blue and green, or a magenta and yellow filters. The paper's emulsions primarily respond to blue and green spectra of the white light. A magenta filter is blue with some red added, to which the paper is not sensitive (within the bounds of normal duration exposures), but which makes the image brighter for the worker. Similarly, the yellow filter, is simply green plus the comfort-enhancing red.

    I would hypothesise that if you used a colour head, by means of which you mix the colour channels, to match the Ilford lowest two grades—contrast range ISO (R) 150–170—you would experience the same wobbliness of the paper's characteristic curve. I do not have such a light source, so I cannot run the test. Even better, if someone else did it, to verify this hypothesis.

    Quote Originally Posted by Bob Carnie View Post
    Until someone can give it a name I will call it a MODIFIED FILTER METHOD... using the outflanking method to determine initial exposure... and 0 and 5 burning in for aesthetic reasons.

    Its no wonder the OP is getting confused,,, the cat is looking better each day btw,, To be fair to both camps , the image supplied would work in Era 1 or Era 2 with not too much issue.

    I just use the MFM method now for all printing as it gets easier over time.
    I think that is the beauty of what we do, there are many ways to arrive at a wonderful result on paper. To some a Les McLean split-grade is the key, as it seems to have helped the OP, to others, like Bob Carnie, MFM, yet others, like John Sexton or Michael 1974, prefer the more old-fashioned approach of building up the grade in small steps. The real jewel is not the knowledge of a general technique, but its very precise detail, such as described so patiently by Bob. These things are not obvious, such as Bob's grade 5 final blast, or like the minor extension of the base time exposure, needed when using the old-fashioned approach while climbing grades, to maintain the highlight density—which split-grade approach does differently.

    Personally, I couldn't figure out my grades without split-grade printing a few years ago, and I have been thankful for that technique. Now I prefer the old-fashioned approach. They both work, and they generate an amazing amount of enjoyable reading on APUG, thanks to which, I get ideas for improving my printing.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  9. #49
    ChristopherCoy's Avatar
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    So, just for shits-n-giggles I went back in and printed this last night just before going to bed. This is Filter 3 @ 10secs.

    Click image for larger version. 

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    And just as a comparison, on the left is the "split grade print" and on the right is the Filter 3 at 10secs. If I were to do this again, which I may do with the two last sheets I have, I would do a filter 3 and dodge the cats left eye, and on the second sheet I would do the split grade thing, but use a filter 4 and burn the fur a little more.

    Click image for larger version. 

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  10. #50
    Bob Carnie's Avatar
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    On either print, back off the density a bit , do everything the same, except burn in the highlighted cats fur with a #5 filter.. just for shits and giggles
    Quote Originally Posted by ChristopherCoy View Post
    So, just for shits-n-giggles I went back in and printed this last night just before going to bed. This is Filter 3 @ 10secs.

    Click image for larger version. 

Name:	CatSG3.jpg 
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Size:	214.0 KB 
ID:	61285


    And just as a comparison, on the left is the "split grade print" and on the right is the Filter 3 at 10secs. If I were to do this again, which I may do with the two last sheets I have, I would do a filter 3 and dodge the cats left eye, and on the second sheet I would do the split grade thing, but use a filter 4 and burn the fur a little more.

    Click image for larger version. 

Name:	comparison2.jpg 
Views:	62 
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ID:	61286



 

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