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Thread: BTZS Subject Brightness Range (SBR)

  1. #1

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    BTZS Subject Brightness Range (SBR)

    Just started to read the BTZS Book by Phil Davis.

    He says to calculate the SBR, subtract the low value from the high value and add the result to 5.

    Is this the same as subtracting the low value from the high value when using a spot meter or are they completely different in terms of the result.

  2. #2

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    Re: BTZS Subject Brightness Range (SBR)

    BTZS does not use a spot meter. An incident meter is used instead. The SBR assumes an automatic range of 5, that is why you add the five SBRs. Using a spot meter is more Zone System oriented. Metering the shadows for exposure, and metering the highs for development.

    From my experience the results you get from an incident meter using BTZS are very different when trying to use a spot meter.

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    Re: BTZS Subject Brightness Range (SBR)

    Quote Originally Posted by aaronnate View Post
    BTZS does not use a spot meter. An incident meter is used instead. The SBR assumes an automatic range of 5, that is why you add the five SBRs. Using a spot meter is more Zone System oriented. Metering the shadows for exposure, and metering the highs for development.

    From my experience the results you get from an incident meter using BTZS are very different when trying to use a spot meter.
    Thank you, I just wanted to confirm my theory

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    Re: BTZS Subject Brightness Range (SBR)

    Quote Originally Posted by aaronnate View Post
    From my experience the results you get from an incident meter using BTZS are very different when trying to use a spot meter.
    I strongly second that statement. A while back, actually several years ago, I tried using both at the same time for the same scenes and found that I was taking more time trying to determine the correct exposure than taking the image. Finally kept on using my spot meter with my modified Zone System as I have been doing since the mid 1970s. Know other photographers who use and love BTZS.

  5. #5

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    Re: BTZS Subject Brightness Range (SBR)

    Well, BTZS book describes several metering recipes.

    IMHO BTZS book has two different sections, first half is sensitometry related knowledge, second half is about recipes for exposure.

    My view is that if we master the first half then it's irrelevant what parctical recipe we use, because we can manage to get similar results by understanding how any recipe works.

  6. #6

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    Re: BTZS Subject Brightness Range (SBR)

    Years ago I learned an excellent method to find the correct developing time and EI for any film. I think the source was an article by William Mortensen. Mortensen wrote some excellent books and articles about basic sensitometry. The last time I did this test was when I abandoned Tri-X and switched to HP5+ due to cost about five years ago. I proceed as follows.

    I set up my trays with my favorite developer HC110B (1:31), now Ilfotec HC (1:31). I pull out a sheet from the package in the dark. and then when the package is sealed again I turn on the room lights. This part of the test is done under the lights. I cut the sheet into five strips and mark them 1-5 by punching holes with a paper punch. Lets say the recommended time is 5:00. I want to see 3:00, 4:00, 5:00, 6:00 and 7:00, so I throw all the strips into the developer and agitate as usual until 3:00 when I move the No.1 strip over to the stop bath. Then I pull No.2 at 4:00, No.3 at 5:00, etc. I fix, wash and dry the strips as usual. What we are looking for is the best usable film DMax value. Obviously the film has been fully exposed! When strips dry lay down a page of news print on a table in good light. Find the strip through which the news print is barely visible. That's your developing time. Now to find the film speed.

    Go outside in unchanging light conditions and expose five sheets and expose one at the manufacturers rating and then the other four at one half a stop and one stop less and one half a stop and one stop more. In the dark, develop them all together for your newly derived time. Contact print them together exposing and developing the paper for maximum usable paper DMax value through the film base plus fog negative rebate area. Pick out the best-looking contact print and you have your film speed.

    Because my 7:00 negative looked the best on the first test, I did the test again with 7:00 as the central developing time and found that 8:00 was indeed too dense. This HP5+ time was the same as the as the developing time I had been using for Tri-X and film speed was also the same, EI400. I have also switched to Ilfotec HC developer due to cost and availability and find it to be a clone of HC110.

    Many of the last generation of B&W gurus favored a development time of 5:00 for Tri-X and suggested an EI of 64-100. You can do the above test backwards, developing for 5:00 minutes and finding the film speed. I like 100. The difference between negatives exposed at 100 and developed for 5:00 and those exposed at 400 and developed for 7:00 is quite subtle. Both could be considered "normal" or N negatives. The 100 negative has slightly greater shadow and highlight detail that only a careful, knowledgeable viewer could detect. This slight improvement might not be worthwhile trading for two stops in the field. I do routinely rate HP5+ at 100 under powerful strobe light in the studio and it produces beautiful skin tones.

    From here, if you are still with me, you can derive expansion and contraction schemes for both the 100 and 400 "normal negs". I do this by changing dilution rather than time. Make sure you have at least 1 oz. of the concentrated sauce for each 8X10 sheet or equivalent. For contractions I found that 3/4 oz. concentrate to 31 1/4 ozs. H20 yields an N-1 neg at a one stop loss in film speed and 1/2 oz. concentrate to 31 1/2 ozs. H20 yields an N-2 neg at a two stop loss in film speed. For expansions, 1 1/4 oz. of concentrate to 30 3/4 ozs. H20 yields an N+1 neg at a one stop gain in speed and 1 1/2 ozs. concentrate to 30 1/2 ozs. H20 produces an N+2 negative with a two stop gain in speed.

    If you look at the chart of Tri-X film speed in Phil Davis' BTZS book you can easily pick out the film speed in HC110B 5:00 as EI 64.

    Don't apply reciprosity exposure and development corrections for long exposures (1/2 sec. +) based on published data. Test for yourself and you may be surprised. I wasted a lot of time and effort producing long exposure negatives that were thick and flat. When I finally tested, I found no compensation was required for TXP or now HP5+ out to one minute.
    Last edited by Neal Chaves; 16-Nov-2018 at 14:17.

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    Randy Moe's Avatar
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    Re: BTZS Subject Brightness Range (SBR)

    Well written!

    Even I understand now.
    TIN CAN COLLEGE

  8. #8

    Re: BTZS Subject Brightness Range (SBR)

    I look at the spot meter and the incident meter as tools that when properly used, both have applicability.

    When you are inside of a circa 1870's miners cabin making a photograph nothing works quite as nicely and efficiently as a Weston V incident meter. Even outside the angle of the sun to the meter and experienced optical flare can mess things up quite easily. Been there and done that. Most times I feel that more reliance upon your eyes to qualify and validate the image area are the highest value components in the produced results. Once you realize that outdoor highlights tend to range in a predictable range and that one can train themselves to see shadow they desire exposure decisions are not statistically that complicated. I like to eyeball the exposure and set the shutter accordingly to the experience factor and then do a quick check with a meter to verify and it is remarkable how close one can get to correct. From my perspective, it is all about results and in that regard, practice makes perfect. Intuitively this process weans oneself off of excessive wasted time holding a meter and trusting your eyes which are ironically what values the tonalities in the final print that is produced. Again, been there and done that X2. Brett Weston in my reading of his field work used his experience in making exposures rarely if ever used a meter. Quickly developing the film and printing the image relative to the notes of the negative and your "feel" of the tonalities desired when making the photograph are the most critical IMHO toward improving your efficiency in the art form.
    Last edited by Michael Kadillak; 16-Nov-2018 at 18:12. Reason: typo

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    Peter De Smidt's Avatar
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    Re: BTZS Subject Brightness Range (SBR)

    Mortensen On The Negative.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer

  10. #10
    Randy Moe's Avatar
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    Re: BTZS Subject Brightness Range (SBR)

    Quote Originally Posted by Peter De Smidt View Post
    Mortensen On The Negative.
    I saw that!

    The Nevada printer Jnanian?(sp) suggested looks good.
    TIN CAN COLLEGE

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