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Thread: Help me in my unbelief!

  1. #1
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    Help me in my unbelief!

    On my way to photographic nirvana - a place of all knowing - I've hit my toe on a rock...

    Please refer to the attached pdf's that are a printout from the BTZS program of a film in a developer. The film and developer are unimportant.

    OK. Here goes...

    In the family of curves, the low curve is for when the SBR is 9.8. The calculated development time is 4 mins, the calculated ISO is 50, the average gradient is 0.34 (I think). The printing of the curves has not shown what is in the program in that the densest sample in the table of results for the 4 min dev is 0.88. The printout is showing a solid line beyond this and the program shows a dotted line.

    Where is the data on this curve? Where are the 9.8 stops? Are they between say the 2.1 and say 0.2 on the horizontal axis? Or would the 9.8 stops be from say the 2.1 to somewhere up in the 'dotted' section?

    As I've learnt that not only do we want a gradient to match a paper we also want the data to fall in a specific range and to top out at a particular density. Perhaps the 9.8 stops tops out on the dotted line at a predetermined density of say 1.35??

    This will then lead to my final question of ... OK so I measure a scene, I get an SBR. I refer to the data for my film and developer. The data tells me to shoot at a particular ISO and develop for a particular time. BUT! When I shoot 'normally' I would place my shadows at say Zone 3 or 2 stops lower than mid. If I have an extended SBR scene of the 9.8 stops for example and follow everything the curves and data tell me do I still place my shadows at the same point or do I move the shadow point to match the shift in ISO? ie move the shadows up the curve away from the toe by placing them at say 'Zone 4' instead?

    I hope this makes some sense!

    Rgds,

    Steve
    Attached Thumbnails Attached Thumbnails Delta 100 76+1 family of curves.pdf   Delta 100 76+1 data points.pdf  

  2. #2

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    Re: Help me in my unbelief!

    Steve, there is always more going on than a simplified model can show.

    Click image for larger version. 

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    In the attached illustration the red lines represent the upper and lower edges of a given paper's range. Black represents normal film development, green reduced development, blue extra development. (This is not to perfect scale, it's exaggerated to show the concept.)

    Camera (film) exposure is represented from left (low) to right (high).

    The blue film curve takes very little horizontal distance to cross the paper's range. For that given paper, only a short range of info/stops from the scene will print.

    The green film curve though takes a longer trek across the paper's range. More stops from the scene will print.

    This assumes no burn or dodge are used when printing.

    The challenge that the BTZS graph doesn't address directly is that of preferred print contrast rate. BTZS is showing you a way to fit the whole scene onto paper without much burn or dodge (normal Zone System also shows you how). That's not a bad thing but the overall contrast of a print from a "green line" negative may lack snap and a "blue line" negative may lack smooth tonality and detail.

    For myself I have found that a well tested normal "black line" development and a bit of burn and dodge gets me results I like better. This also leaves me room to use variable grade to fine tune. Variable grade paper moves the red lines closer or farther apart.

    Enlarger exposure moves the red lines up or down in tandem.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  3. #3

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    Re: Help me in my unbelief!

    On the typical H-D curve, the X axis uses log luminance - so every 0.3 represents a doubling of luminance. The Y axis represents the density on the negative. So a 5 stop range will be represented by a 5 X 0.3 = 1.5 range on the X axis over which the curve is responsive (i.e., changing). In other words, on the extreme left (very low luminance - deep shadows), the curve is flat - changes in luminance do not register on film. At some point, the curve starts moving upwards (the film-developer combination starts building density on the negative). As this moves upwards, you will reach a point where the density is so high that you will still see white areas on the print if you select a print exposure that reproduces the bottom end of the curve (the shadows) with detail (i.e., the shadow areas do not block up). So you should select a slope for the curve that will let you 'automatically' produce whites with detail in the regions you want while holding detail in the shadows. In other words, the subject luminance range that you select should print with a 'full scale' (paper white - in practical terms, defined as 0.04 density above base + fog of paper - to maximum black - in practical terms 90% of the maximum density the paper is capable of). So, if you have a short subject luminance range (less than 1.5 on the X axis), you want the slope of the curve to be steeper and if you have a long subject luminance range (more than 1.5 on the X axis), you want the slope to be less steep.

    In other words, any paper is capable of handling a certain density range negative. You want to develop negatives so that the subject luminance range provides this density range on the negative, so that the negative is matched to the paper.

    When you develop for a shorter time because you are trying to handle a long subject luminance range (a contrasty subject), you are effectively reducing the slope of the curve so that you still have the same negative density range that the paper can handle. While the top end of the curve has a bigger change in density than the bottom end, there is still a change at the bottom end. In other words, theoretically, the bottom end should not change (i.e., your film speed - the minimum luminance required to get some density above film base plus fog) should not change. But practically, there is often a small change in speed - the point at which the film starts responding shifts slightly. So in practical terms, if you are doing N- processing, you are likely to require somewhat more exposure (i.e., you lose film speed).

    So in answer to your last question, your zones do not change. You still decide which areas in the subject should be zone 3 and which should reproduce as zone 8 or whatever. However, in order for your zone 3 in the scene to provide enough density on the negative to appear as zone 3 on the print, you will find you need to add some exposure (usually along the lines of 1/3 stop to a stop depending on how extreme the pull processing is, the specific gremlins in your darkroom etc).

    Hope this helps. Cheers, DJ

  4. #4
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    Re: Help me in my unbelief!

    OK. So taking your thoughts DJ, I shoot with the same mantras regardless of SBR and ISO figures coming out of the BTZS programs. That is, if my mantra is to pin the shadows at Zone 3 then I continue to do so. All I do is adjust ISO a little and develop according to the BTZS program outputs.

    Mark, I take it the BTZS graphs I gave do not have the full picture then. As you've drawn, the horizontal red lines indicate an 'ideal' boundary of exposure which is not seen in the BTZS plotter program.

    Thanks for your replies.

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    Re: Help me in my unbelief!

    Quote Originally Posted by swmcl View Post
    Mark, I take it the BTZS graphs I gave do not have the full picture then. As you've drawn, the horizontal red lines indicate an 'ideal' boundary of exposure which is not seen in the BTZS plotter program.

    Thanks for your replies.
    No, not the boundaries of film exposure, ideal or otherwise, the red lines simply represent the "real" limits of the range of detail that the paper can print.

    Negatives typically catch more detail, many times a lot more detail, than might be intended to straight print. Detail on the negative below the lower red line simply prints pure black, detail above the top red line simply prints as pure white.

    Having this extra unused detail on a negative is normal, right, and proper. Our ability to burn and dodge most negatives to get more detail on a print is the real life proof.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  6. #6
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    Re: Help me in my unbelief!

    Hi Mark,

    Yes this is what I meant and understood. The plotter program omits the horizontal lines which is the paper limits. I guess the next thing to be found will be developer exhaustion. I haven't seen too many curves showing limits there!

    I'm expecting developer exhaustion would show a shoulder in the curve hopefully some fair distance above the section we wish to print. A postal damaged densitometer should arrive for me this week. I look forward to the next phase in my learning.

  7. #7
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    Re: Help me in my unbelief!

    The reason I'm so interested in developer exhaustion is because it would be good to know just how little - in terms of ml per sq inch - one can go before trouble begins. This would be especially for the longer development curves.

    Its not that I want to use as little as possible but that I want to know I am not compromising my efforts. I guess one could just forget it and double the mixture to be sure, I know that there are experienced practitioners here who do just that.

  8. #8

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    Re: Help me in my unbelief!

    It would take some work to figure out and would be tricky to use in the field.

    Part of the problem is that the amount film exposure given changes how much developer gets used up. A scene with a lot of bright subject matter or that is given some extra general exposure will use up developer more quickly than a scene with mostly dark subjects or minimized exposure, this is because the developer has more silver to react with.

    There is no good way I could judge or adjust for this so I stick with recommended volumes and recipes.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

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