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Thread: BTZS Metering Question ...

  1. #1
    Rick Olson's Avatar
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    BTZS Metering Question ...

    I am utilizing the BTZS system for exposure and using an incident meter to assess shadow and highlight SBR values. The BTZS book, along with other written sources, advises that when using an incident meter, measurements are done aimed at the camera lens.

    I have attached an image to help explain my question ... I am shooting a railroad shed with the sun behind me and rising (AM). Using my meter, I measure the shadow value at EV9 and the highlight value at EV14, for an SBR of 10. I make my exposure and development notes and take the shot. For this image, my meter was aimed at the camera lens (as per established practice) and was pointing in the direction of the light source (sun) for the highlight value (again ... the sun was behind me).

    Here is my question:

    I now want to take an image at a 45 degree angle to the shed, so I move my camera off to the side. Using the practice of keeping the meter pointed at the camera lens, I take my shadow reading ... still at EV9. In taking the highlight value, the reading is different and lower at EV13. This because the dome of the meter is no longer directly pointing at the sun, but slightly shaded due to the 45 degree angle I am now using it at.

    Now, there has been no change in the lighting ... same shadows - same bright morning sunlight hitting the walls of the shed. I have only moved the camera at an angle. In my thinking, there should be no reason to change the exposure since there has been no change in the light. If I do change, I am looking at possible burned out highlights.

    Would it not be best to measure ONLY the contrast values (shadow and highlight), considering the image before you and take the shadow reading and then aim the meter toward the sun for the highlight? If I do this, I will have uniformity of contrast measurement. If I keep shifting the meter to face the camera, I will probably be fine with my shadow measurements, but my highlight data will be inconsistent.

    Looking forward to your responses ...

    Thanks!
    Rick

  2. #2
    Chuck P.'s Avatar
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    Re: BTZS Metering Question ...

    Quote Originally Posted by Rick Olson View Post
    Using my meter, I measure the shadow value at EV9 and the highlight value at EV14, for an SBR of 10.
    I probably won't be of any help to you, I'm a ZS guy myself and use a spot meter to measure SBRs, and not familiar with BTZS practice of metering. But can you explain how EV9 to EV14 is a SBR of 10 stops, if indeed it is stops that you are referring to. By my measure that is a 5 stop SBR or 32:1.

  3. #3
    ic-racer's Avatar
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    Re: BTZS Metering Question ...

    I'm not familiar with how BTZS asks one to determine calibration with the incident meter, but why would you change exposure if the shadow reading does not change? Does it say to do so?

    I suspect the near unanimous answer the question is going to be as stated above by Chuck: "use a spot meter"

  4. #4
    おせわに なります! Andrew O'Neill's Avatar
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    Re: BTZS Metering Question ...

    Whatever exposure you used for the first setup, should be okay for the second setup, as long as the light did not change.
    On another note, have you considered using a reflective metre? I find them to give more control over the subject's values than an incident metre. Just my opinion.

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    Re: BTZS Metering Question ...

    Rick,

    Where are you standing to measure the shadow value. It looks to me like there is no texture at all in the deep shadows of the building, and I would want to see detail in there. If you measure at the back wall of the building the shadow density and then measure highlight density in the sun you should get a much higher value than SBR 10. I am guessing that that scene should be about an SBR of at least 15 or higher.

    To capture that range on film I would suggest a two bath developer, perhaps Diafine or two bath Pyrocat. You can plenty information on two bath Pyrocat at www.pyrocat-hd.com/ Two bath development is not then only way to capture a scene of high contrast, but after using all of the other methods I believe it is the best method, and I have exposed many, many negatives with subjects of very great SBR.

    As for how to measure, if using an incident meter always aim the meter right at the lens of the camera. Any other method will distort the true SBR in one way or another.

    Sandy
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    Re: BTZS Metering Question ...

    The lighting did change. The light falling on the film is reflected at a 45 degree angle from the subject, and so one stop of highlight value is lost. Trust the method. How important is the difference between SBR 9 and 10? Try it both ways, and see for yourself.

  7. #7
    Rick Olson's Avatar
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    Re: BTZS Metering Question ...

    Thanks everyone ... I appreciate the comments. I will "trust the system" and will continue with more practice. Anything to stay out shooting.

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    Re: BTZS Metering Question ...

    Quote Originally Posted by Chuck P. View Post
    I probably won't be of any help to you, I'm a ZS guy myself
    Chuck you answered his question perfectly.

    Quote Originally Posted by ic-racer View Post
    I'm not familiar with how BTZS asks one to determine calibration with the incident meter, but ---------------
    Incident metering is every bit as accurate and much faster than a spot meter ---- with BTZS.

    There seems to be a rapid response most often to BTZS questions from people who have little or no understanding about the methods. Both the ZS and BTZS produce excellent results just that one does it much more repeatably.

  9. #9
    Chuck P.'s Avatar
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    Re: BTZS Metering Question ...

    Quote Originally Posted by Steve Nicholls View Post
    Chuck you answered his question perfectly.



    Incident metering is every bit as accurate and much faster than a spot meter ---- with BTZS.

    There seems to be a rapid response most often to BTZS questions from people who have little or no understanding about the methods. Both the ZS and BTZS produce excellent results just that one does it much more repeatably.
    I was only being truthful---I'm not familier with BTZS metering practice. Perhaps he could shed some light on what I was asking him about. Perhaps I felt it might help me to understand his question better, perhaps it would be beneficial to my understanding of BTZS. Maybe not.

    Rapid response? Yep, been sittin here all day waiting for a BTZS comment to contradict---come on.

  10. #10
    ic-racer's Avatar
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    Re: BTZS Metering Question ...

    Quote Originally Posted by Steve Nicholls View Post
    Chuck you answered his question perfectly.



    Incident metering is every bit as accurate and much faster than a spot meter ---- with BTZS.

    There seems to be a rapid response most often to BTZS questions from people who have little or no understanding about the methods. Both the ZS and BTZS produce excellent results just that one does it much more repeatably.
    Out of curiousity can you tell us how BTZS has one calibrate the incident meter? The website does not say.

    Personally I like the have the lowest values with detail fall about 4 to 5 stops below the indicated incident exposure with sunlight scenes and 2 to 3 stops below for flat-copywork. Just curious what Phil likes.

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