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  1. #141
    Bill Burk's Avatar
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    Whether or not you zero out your densitometer on Base + Fog is significant but it is a very small discussion point.

    I don't have a dogma about it, but I take a reading for Base+Fog then zero the densitometer on Base + Fog and read the rest of the numbers.

  2. #142
    Stephen Benskin's Avatar
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    Quote Originally Posted by PeterB View Post
    There are however two points which conflict with 0.17 being a relative measurement above B+F.

    1. In the Figure 4 above, the RHS column shows Zone II beginning at 0.17 rather than Zone 1.5
    2. All the density measurements done thus far for the spreadsheet and entered into the "Input Data" tab (fig 3 in Ralph's pdf) are absolute values, but in point 9. above, there is no mention that 0.17 is a relative value in the instructions.

    Can anybody explain why Zone II is beginning at 0.17 and reassure me that 0.17 is actually a relative density measurement ?
    It’s hard to figure out where to begin. There’s the concept of speed point and exposure placement and how they are two different things. There’s also the question of the accuracy of Zone System testing. But I’ll attempt to limit it to the question at hand.

    Bill pretty much answered question 1. The range for a zone is from -1/2 to +1/2 of that Zone with the Zone number falling in the middle.

    As for the second question, it’s all relative with the film curve because apart from using Zones as a guide between the original subject and the paper curve, Zones have little relevance when it comes to the film curve. There simply isn’t a fixed relationship between Zones and negative densities.

    The scene has a luminance range and camera exposure places it on the film curve. The key is to place the scene’s values on a portion of the curve with a sufficient gradient to separate the tones on the print. Increasing or decreasing the exposure moves the entire illuminance range up or down the curve, but the luminance range of the scene remains the same.

    In other words, the illuminance value that falls four stops under the metered exposure point is considered Zone I when shooting a 100 ISO film rated at 50 and it is also considered Zone I when shooting a 100 ISO film rated at 100. Using Ralph’s 0.17 as a speed point decreases the film’s EI as it relates to the 0.10 speed point by ½ to 2/3 of a stop depending on the curve shape and average gradient. This just shifts everything to the right 0.15 to 0.20 log-H units. The shadow falling four stops down from the metered exposure point doesn’t change from Zone I to Zone I ½ .

    How it is illustrated in Ralph’s graph only works if you consider he is referencing how the change in exposure compares to using 0.10 as the speed point.

    Figure 1 illustrates the relationship between the subject’s Zones and there placement on the film curve placing Zone I exposure at 0.10 over Fb+f.

    Figure 2 illustrates the relationship between the subject’s Zones and there placement on the film curve placing Zone I exposure at 0.17 over Fb+f. It can also be considered simply increasing the camera exposure by 0.20 log-H units (2/3 stop).

    Figures 1 and 2 represent the relationships in a non-flare environment such as during testing. Actual shooting conditions include flare.

    Figure 3 illustrates how flare changes the relationship of the illuminance values with the subject luminance values. Everything is the same as with Figure 1 except for the addition of flare and an adjustment in the camera exposure in order to place the flare shadow exposure at 0.10 over Fb+f.

    Figure 4 can be considered the type of results that are obtained using Zone System testing with 0.10 as the speed point. With ZS testing there is little flare. An exposure four stops down from the metered exposure point excluding flare will fall on 0.10 over Fb+b, but with the addition of flare that exposure produces a higher film density, but it is still considered a Zone I exposure. As flare varies from scene to scene, it is impossible to predict exactly where the shadow exposure will fall for a specific scene.

    What makes Ralph’s example confusing is that he suggests decreasing the film’s EI to increase the exposure by approximately ½ stop, yet what he seems to be describing is a change in the scene’s luminance distribution. Figure 5 illustrates a change in the distribution of the luminance range from Zone I to Zone VIII to Zone I ½ to Zone VIII ½. While this will shift the exposure to the right on the film curve, the mechanism isn't the same as changing the EI.
    Attached Thumbnails Attached Thumbnails Zones and Exposure Placement.jpg   Zones and Exposure Placement 2.jpg   Zones and Exposure Placement 3.jpg   Zones and Exposure Placement 4.jpg   Zones and Exposure Placement 5.jpg  


  3. #143
    CPorter's Avatar
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    [QUOTE=Stephen Benskin;1273074]

    For those that do not have a lot of other highly technical sources and refference material on hand, the concepts being addressed are found in The Negative. This text has often been criticized for representing "bubble gum" sensitometry, but if it was too overly technical, it would be criticized for that as well.

    Bill pretty much answered question 1. The range for a zone is from -1/2 to +1/2 of that Zone with the Zone number falling in the middle.
    Just chiming in that this is mentioned in The Negative on page 52, although not as in great detail, but it doesn't have to be either. It states that the individual gray values produced at each zone are the midpoint of their respective zone.

    As for the second question, it’s all relative with the film curve because apart from using Zones as a guide between the original subject and the paper curve, Zones have little relevance when it comes to the film curve. There simply isn’t a fixed relationship between Zones and negative densities. The scene has a luminance range and camera exposure places it on the film curve. The key is to place the scene’s values on a portion of the curve with a sufficient gradient to separate the tones on the print. Increasing or decreasing the exposure moves the entire illuminance range up or down the curve, but the luminance range of the scene remains the same.
    Not disagreeing, this is also covered in the book very adequately IMO and without any unnecessary verbage on page 67-69 in the discussion of "subject contrast", specifically regarding the short-scale low contrast subject. The Chapter on the ZS covers these things, IMO, in practical and understandable terms, but not without some personal indeavor to "see" it. Regardless of how this stuff is discussed, either in a more simpler or complicated manner, it will never, IMO, be immediately obvious.

    It clearly covers, IMO in the ZS chapter, that a subject luminance ratio, for example, of 8:1 remains 8:1 between any 4 zones on the log exposure scale, be it between Zone III and Zone VI or between Zone IV and Zone VII, between Zone V and Zone VIII, etc....

  4. #144
    Stephen Benskin's Avatar
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    Maybe these two examples will help clear up my point. The four quadrant curve should illustrate the difference between changes in exposure and changes in luminance. The second example is an adjustment to Ralph's illustration.
    Attached Thumbnails Attached Thumbnails Exposure and Luminance.jpg   Ralphs Adjusted Example.jpg  

  5. #145
    PeterB's Avatar
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    Stephen, thank you for your detailed reply.
    regards
    Peter

  6. #146
    PeterB's Avatar
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    Quote Originally Posted by PeterB View Post
    I will finish documenting my film speed test results here.
    I wanted to share my latest version of the film testing spreadsheet. In summary I have made changes to permit the user to adjust their target density range. Ralph had defaulted it to 1.20 in many places (as he targets grade 2 paper in a diffusion enlarger). But because others will use condenser enlargers etc, I wanted to share my changes.
    I replaced all instances of the 1.20 constant with a user adjustable value on the first worksheet (Input Data, cell K66). The value I adjusted mine to was 1.05 because I have a condenser enlarger (which would usually take it down to 0.9 as a starting point), but my camera system is susceptible to a reasonable amount of flare so I increased it by 0.15 to 1.05.

    FilmTestEvaluation #003 of Ilford HP5plus 120 in XTOL 1+2.xls


    Now it is rather late in my evening and I want to get clarification on a major concept. On p. 7 of Ralph's PDF instructions in this thread (also in WBM p. 139), Ralph plots the Effective Film Speed versus Zone System N. I'm embedding the one I've come up with.
    Click image for larger version. 

Name:	Effective Film Speed vs Zone System N.jpg 
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    My normal (N=0) EI turns out to be 252 (no surprise there as it is 2/3 of a stop below the nominal 400). Hence for an N=0 scene with SBR=7, I would set my light meter to ISO 250, meter a Zone III part of the scene and expose accordingly.

    Now, if I photograph a scene that is say N+2 (i.e. with a SBR=5), do still have my light meter set to ISO 250 or do I set it to the value of 650 shown in the above graph ? I'm pretty sure I leave it at 250 and I know I could answer this question myself by thinking about it and doing more reading, but right now it is late and it is quicker for me to type these 2 paragraphs and get a quick answer from the experts. Soon all this will be 2nd nature to me, but right now I am taking it one step at a time. BTW if you do happen to answer, please don't feel obliged to give a really long explanation. Just a simple yes or no will be plenty !

  7. #147
    Stephen Benskin's Avatar
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    If you feel your testing method is accurate, then you adjust the EI; however, it's not an absolute requirement.

  8. #148
    PeterB's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    If you feel your testing method is accurate, then you adjust the EI; however, it's not an absolute requirement.
    Thanks Stephen. I had forgotten that the shadow transmission (Tx) density increased with increasing film dev time. I should have remembered this last night when I posted, but my brain was shutting down as it was late.
    The highlight Tx density on the neg increases much more (with increasing film dev time), the shadow Tx density does still increase to a lesser extent and this is catered for by giving less exposure by increasing the effective film speed. This is obvious to me now since the Family of Curves worksheet clearly show each toe region being higher in Tx density than the last as the film dev time is increased. Ralph points this out at the end of p. 139 in WBM (and prob. in many other places in WBM too).

    I'm happy that my test method is sufficiently accurate for my initial attempts. Assuming I didn't make any unintentional errors then the only thing I would change if I retested would be to reduce my exposure times to get more of the toe in for each of the 5 films. I did get one point on 4/5 of the toes, the last one I guessed to match the obvious pattern that emerged. Full details specific to my testing efforts are in the spreadsheet I attached in my last post.

    rgds
    Peter

  9. #149
    CPorter's Avatar
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    Been looking at the spread sheet, the 21st or 31st step is shown as being the chemical fog density, but these are defined steps and clearly, at least from my tests, contain density both from exposure and chemical fog. It's just an observation. I use a piece of black electrical tape in the middle between the rows of step densities to ensure there is an adequate section of the tablet that does not receive exposure from which to read just chemical fog density, but that's just me.

  10. #150
    PeterB's Avatar
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    Quote Originally Posted by CPorter View Post
    Been looking at the spread sheet, the 21st or 31st step is shown as being the chemical fog density, but these are defined steps and clearly, at least from my tests, contain density both from exposure and chemical fog.
    This will depend on how much exposure you give the step tablet. Ideally one wants at least step 31 to be in the Base+Fog. In my case I had applied too much exposure and I got none of the 31 steps close enough to the B+F. I got plenty of film shoulder but little or no toe. I had to discard the shoulder points as they are of no use in this particular test. I did get one significant point in the toes of 4/5 of the films using an X-rite four step cal tablet whose darkest density is 3.80 . I used that tablet along with Stouffer 31-step. The darkest step(#31) on the Stouffer 'only' had a density of 3.05.

    Anyway my point is that in my testing, step #31 certainly produced a density much higher than the base+fog level on each film. B+F was 0.11 to 0.15 for my 5 films (increasing with increasing dev time). The neg Tx densities for step 31 were 0.29 (G23), 0.19 (H29), 0.24 (I29), 0.31 (J29) and 0.37 (K29). The first value (0.29) seems too high, but I used a longer shutter speed on that film compared to the other 4 (using 2 shutter speeds introduced another complication as the mechanically timed shutter speeds aren't exactly integer multiples of each other, but I did measure their exact speeds separately).

    The other thing you may find confusing on my Input Data worksheet is that those 5 points above do not line up with row 41 (being step#31). this was because I shifted the relative placement of my curves up to simulate a reduction in exposure because I over exposed the steps. See posts #124 and #128 from me above which detail this a bit more.

    Quote Originally Posted by CPorter View Post
    It's just an observation. I use a piece of black electrical tape in the middle between the rows of step densities to ensure there is an adequate section of the tablet that does not receive exposure from which to read just chemical fog density
    Make sure your tape lets negligible light through. I just measured the Tx density of piece of black PVC electrical tape and it was at least 5.0 which should be fine. Mentioning that reminds me of how for too long I used pieces of unexposed, fixed and washed MG IV RC paper for a dodging/burning mask. The paper would let through a small amount of light and sometimes just subtly flatten the areas under the paper.


    regards
    Peter



 

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