Incident Meter & exposure for shadows.

Discussion in 'Exposure Discussion' started by baachitraka, May 10, 2012.

  1. baachitraka

    baachitraka Subscriber

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    Hello,

    BTZS suggest to incident meter the shadows and highlights, find the difference and add five stops to it to get Scene Brightness Range.

    - Look SBR vs EFS charts to find appropriate film speed.

    - Set the film speed in the meter and use shadow reading to determine the exposure.

    - Developing time is obtained from SBR vs Development time charts.

    My understanding is, when metering shadows the incident meter will place the shadows to middle gray then how we can use this to determine the exposure as according to BTZS method. Since, shadows will be on middle gray.
     
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  2. markbarendt

    markbarendt Subscriber

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    Incident metering measures the incident light in the shaded areas, not the intended black point on a film or paper curve.

    Assume for a second that you are doing a backlit portrait, sun behind your subject. The "highlight reading" is taken from the sunny side, meter on the back of your subject's head, the "shadow reading" is under your subject's nose. The "shadow reading" by itself places the face at a fairly normal zone 6ish in relation to that reading.
     
  3. Bertil

    Bertil Subscriber

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    At least this should be true: measuring incident light at the shadow side of the subject (i.e.the opposite part of the subject lit by the main light) will place middle grey PARTS of the subject at the shadow side middle grey (given normal development and appropriate film speed). This is roughly definitional (and what Mark has in mind I suppose). If this is what You mean by "shadows will be on middle gray", then something is wrong with BTZS (probably not) or this understanding of the system, if it's supposted to be a proper guide to how to expose/develop for a proper picture. Normally, if the main part of the picture is in the main light with highligts and middle grey these part should show up as highligts and middle grey, middle grey parts in the shadow side (grey chart in the shawow!) should not (normally!) show up as middle grey, rather steps darker.

    Well, someone more acquainted with the BTZS, SBR and EFS will probably give you more advice on this subject. (Personally my standard method is to measure the incident light on the shadow side and underexpose that roughly 2-3 steps, if the contrast is quite normal, and just 1-0 if I plan to do a more soft development due to the contrast, since in that case some shadow density will get lost. This is not very precise as I suppose BTZS pretend to - but works normally quite nice.)
    /Bertil
     
  4. benjiboy

    benjiboy Subscriber

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    If you want to asses the Subject Brightness Range with an incidental light meter using this Duplex Method, or to asses the contrast ratio given by individual lights or strobes in the studio it's best to do it with a meter that has a flat plane diffuser rather than a dome one, because it only sees the illumination directly from the front of the meter to get the most accurate results.
     
  5. markbarendt

    markbarendt Subscriber

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    The wild card with BTZS is the "adjustable" EI. Adjusting the EI moves the placement of the subjects on the film curve and subsequently the print.

    The meter reading is simply the reference point, the system places the subjects rather than the meter.

     
  6. baachitraka

    baachitraka Subscriber

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    I presume it is one of the clever system devised by the master.
     
  7. markbarendt

    markbarendt Subscriber

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    Actually it's the way all metering and exposure setting works. BTZS is just "packaged and sold as a system". It's worth every penny for many people, for others it's just another way of doing the same thing they are already doing.

    Using an incident meter and say Ilford's directions is not that much different, it just doesn't give you directions on how to pick the EI, like BTZS does. The film, the processing, and the metering though are just keyed to industry standards rather than specific film testing.
     
  8. Mahler_one

    Mahler_one Member

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    I'll leave it to Fred Newman to comment in more depth, but I believe that Mark is quite right. The metering done in BTZS is with the ASA set at 100; one is simply reading the values of the highlights and the shadows without any attempt to use such metered values to calculate the exposure. Based upon the testing of one's film, one uses the results to determine the SBR AND most importantly, the EFS at the SBR in question. Using the EFS ( which is then set into the meter in place of the ASA 100 ) allows one to use the shadow value(s) to correctly expose the negative. What is as yet unsaid is that one can quickly learn to use the placement of the incident meter so as to render the shadows however one desires, i.e., to obtain more or less shadow detail. As Mark writes, there are points to be made for the classic zone system using reflected metering, and BTZS using incident metering. In either case, testing of one's materials is integral to obtaining the "correct exposure". Furthermore, experience and experimentation will allow one to use either system to use "creative" exposure so as to obtain prints that reflect one's sense of how the scene in question is to be interpreted.

    I use BTZS with the ExpoDev program, and I would never go back to the Zone System. However, again as Mark correctly infers, use whatever "system" of film exposure and development works for you. One is not "better" than the other. Indeed, if one learns to develop by inspection, simply expose for the shadows at a film speed that yields good shadow detail, and pull the negative from the developer when the highlight details are "right"! Grist for another mill.....
     
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  9. baachitraka

    baachitraka Subscriber

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    I'm learning, I'm learning...

    How are modern incident meters? Master was explaining that meter's cells(presumably old meters) sees the world as five stops but the calculator dial seven stops. So metering shadows will overexpose by a stop and vice versa for highlights.
     
  10. markbarendt

    markbarendt Subscriber

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    I use a Sekonic L 358. It has a 14 or 15-stop range if I remember right. Can't help with the old meter. One thing that may help you is to think about what the meter is telling you as a reference point. There are good reasons to deviate for the meter's suggested settings.