BTZS Exposure and Development Question

Discussion in 'Exposure Discussion' started by Paul, Oct 19, 2006.

  1. Paul

    Paul Member

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    Hi,

    I recently photographed a scene that raised an exposure question or two in my mind, and I am hoping that the wise BTZS users out there might share their thoughts.

    The scene was an old condemned house in bright afternoon light. There were not any large or significant shadow areas, but I metered a shadow on the lawn just out of the frame since this appeared to be the same as the smaller un-meterable shadows under the roof line and beneath the wooden shingles that covered the side of the house. The difference between the low and high EVs indicated a SBR of 9. That was higher than I expected, but I metered it several times and each time I got identical results. So, I based my exposure on the shadow reading and indicated appropriate development. As an experiment I took another shot assuming a SBR of 7 since it “felt” like a 7 stop scene. (I simply took the high reading and subtracted 2 stops from it and took that as the new shadow reading and based the exposure on it). The film was TMAX 400.

    I developed both negatives for the appropriate times in Pyrocat HD 2:2:100 (in this case 7.25 minutes for the SBR 9 neg and 11.5 minutes for the SBR 7 neg). I have not printed them yet, but both negatives look very good. However, the SBR 7 neg has slightly more contrast and looks to be the one that will print the best based on past experience. Still, the differences are subtle. My questions:

    1. Given that Tmax 400 has a very straight line, shouldn’t it be possible to take two shots of the same scene at different exposures and get essentially identical negatives by developing each for the appropriate time? Shouldn’t it be impossible for me to tell these two negs apart if both were developed just right? Or is it impossible to ever achieve this since each negative has its values placed on different parts of the curve (straight though the curve may be?)

    2. If it is true that one can make two identical negatives this way, would this not be a good way to test development times? I know for example that 11.5 minutes works well for scenes where the SBR is 7. If I shoot the same scene as a 7 and a 9, with adjusted exposure, would it be safe to assume that my development times for a scene with an SBR of 9 is dialed in when it looks (and prints like) the SBR 7 neg?


    Thanks,
    Paul
     
  2. Paul

    Paul Member

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    P.S. Sorry that came out so long.
     
  3. Robert Hall

    Robert Hall Subscriber

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    No on the first one. Asking that question states that you feel the shadow values will develop "up" to same level for each negative. Remember expose for shadow, develop for highlights? Shadow values will be different for different exposures. Highlight differences will be different for different development.

    This does not mean you can't play with the contrast in printing to get a similar print however --using vc paper or sundry methods of developing the print. That is one of the nice things about B&W, it's most forgiving.

    As for question 2, remember you are trying to match the final curve of the film for a given SBR to match the curve of the paper (usually centered around grade 2, but this can be changed by adjusting exposure and development.)

    Also remember that film, developer, the SBR, and the paper you choose to print on all have an effect on the final print. Change can be made to 2 variables to get a similar, final print.

    Regards,
     
  4. Paul

    Paul Member

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    True, silly of me not to think of the shadows being exposed differently. I guess what I should have asked, is whether it would not be possible to get the two negatives to share nearly identical highlight density?
     
  5. Robert Hall

    Robert Hall Subscriber

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    Not silly at all.

    The answer --then-- is of course. (and within reason due to the limits of film density.)
     
  6. Paul

    Paul Member

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    I printed both negatives yesterday. The one exposed for the full SBR of 9 prints much better than the one treated as an artificial SBR of 7. Unfortunately I chose this moment in my life to switch thermometers and both appear to be overdeveloped a smidge. Live and learn.

    -Paul
     
  7. Robert Hall

    Robert Hall Subscriber

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    Somone said buy 2 that are the same and measure the same, then hide one. :smile: I try to find 5 or 6 the same on ebay about every 5 years.