Contrast and incident metering

Discussion in 'Exposure Discussion' started by Marc Leest, Jun 9, 2005.

  1. Marc Leest

    Marc Leest Member

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    Hello,

    How do you determine negative contrast with a incident meter ?

    Is this assumption correct:

    First, meter the EV pointing to the camera, secondly meter the EV pointing to main lightsource (sun).
    Substract both values to have the contrast range.

    Any tips? thx, Marc.
     
  2. noseoil

    noseoil Member

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    Marc, I don't have an incident meter, but I wouldn't take any readings off of the sun. I think you would do as you have said, but slightly differently. Point the meter at the camera for overall light falling on the subject. Find the lowest value which needs detail and read this as a shadow value. This can be done by using your other hand as a shade to find low values. From what I've heard, the shadow values are the tricky ones, because the reading is a bit more subjective than a reflective meter's reading of light bounced off of a darker area.

    I'm sure others will correct me on this one, but I think this is basically correct. My understanding is that the lower the scene's contrast, the more experience and judgement play a role with incident meters. tim
     
  3. Donald Miller

    Donald Miller Member

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    First you would point the dome of the incident meter toward the camera lens from a fully lit position, second you would point the dome of the incident meter toward the camera lens from the shaded position. Determine the EV from the sunlit position and the EV from the shaded position and add the difference between the two EVs to five. This gives you the SBR of the scene.
     
  4. benjiboy

    benjiboy Subscriber

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    I have used for quite a few years the incidental light metering procedure described in The Exposure Manual by Dunn, he calls it the Duplex Method, in which you point the dome of the meter at the sun, and note the reading,then from the subject to the camera note that reading setting your exposure between the two. I have found that this works, no matter if it's frontal, side or backlighting
     
  5. Max Power

    Max Power Member

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    Hello Donald,
    I have a question. I went outside and took the EVs for shade and fully lit and added the difference to five. Now my stupid question: what do I do with this number? What is an SBR?

    Thank you,
    Kent
     
  6. Donald Miller

    Donald Miller Member

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    This adjusted number would be your SBR. That is the "subject brightness ratio" for your conditions. If the SBR is 7 it is normal. If it is greater then 7 then you would adjust development to reduce inherent scene contrast. If it is less then 7 then you would increase development to increase inherent scene brightness. If you use Pyrocat and any of the films that Sandy King has tested, you will be able to arrive at development times for different SBRs. A good source of this information is on unblinkingeye.com
     
  7. Claire Senft

    Claire Senft Member

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    It may be helpful to understand why you add 5 to the difference in stops. 5 has been chosen because the greatest difference between the whitest white and darkest black that can be created with paint is approx. 4 1/2 stops rounded off to 5 for nominal use. Therefore if the difference between lit and shadowed areas is two stops you have the potential for 7 stops of difference between the whitest white in light to the darkest black in shadow. Such differences may not exist in the actual scene being photographed but are provided for in the exposure and development chosen.
     
  8. Max Power

    Max Power Member

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    Claire and Donald,
    Thank you both for the explanations. I have learned something new.

    Kent
     
  9. Bruce Osgood

    Bruce Osgood Membership Council

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    ME TOO. Thanks.