LV and EV?

Discussion in 'Beyond the Basics' started by panzershreck, Aug 6, 2005.

  1. panzershreck

    panzershreck TPF Noob!

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    anybody care to explain this to me?

    I understand that Exposure Value corresponds to aperture and shutter speed to get similar exposures, 100 ISO is a 1 to 1 ratio, and each film speed greater or lower is 1 fstop difference (ISO 400 = +2 fstops, ISO 50 is -1 fstop), and that EV also operates in the same fashion corresponding to the LV (on a scale, EV 0 = f1.0 at 1sec)

    Light Value is the light level reflected by an object (black would be less than white), and is measured in a scale (commonly LV18 for a lot of light through negative LV's for night)

    therefore, an LV of say 14 would be EV 14 for ISO 100 (1/125 @ f/11), EV 13 for ISO 50, and EV 16 for ISO 400, etc.

    is this correct?
     
  2. selmerdave

    selmerdave TPF Noob!

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    I don't know a whole lot about LV but it seems to me that EV usually refers to incident light, so if LV is reflected light that's a difference. Exposure is a function of incident light, the reflected light is what fools light meters when there is a large or small amount of it. Under the same incident light one would use the same exposure settings for a white object or a black object, despite what would be different values of reflected light.

    Also, EV 14 is EV 14 regardless of film or aperature settings, the film speed determines the aperature and shutter speed combinations that provide proper exposure at that light level.

    Dave
     
  3. wharrison

    wharrison TPF Noob!

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    Panzershreck:

    I hope the following helps to clear things up. I did a search on Google.com for "Understanding Exposure Meters" and, after a little searching, the following information popped up.

    The first on "Exposure Value" came from the site listed below, which offers a wide selection of photographic terms.

    http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/



    The site listed below offers a brief, but good discussion of "understanding exposure " and provide you with some illustrations.

    http://luminous-landscape.com/tutorials/understanding-series/understandexposure.shtml

    A comparative discussion of LV and EV was found at the site below and should also be very helpful

    I've posted it as a second installment.

    More to come . . .
     
  4. wharrison

    wharrison TPF Noob!

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  5. selmerdave

    selmerdave TPF Noob!

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    Mr. Rockwell has a good and detailed explanation. The only problem I have is that he doesn't make much mention that his method of determining exposure using LV's does so with the assumption that the subject is basically gray. Calculating exposure this way with either highly reflective subjects or those that are very light or dark in colour will give considerably under and over exposed results.

    Dave
     
  6. wharrison

    wharrison TPF Noob!

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    Dave:

    This is one of the very reasons, why I don't bother with EV or LV and make use of a hand held meter and use an "interpreted" (from my own experiences) incident light method. Works wonders even in a theatrical situation.

    But then I also - sometimes - read the play; attended one or two dress rehearsals; and then took incident light meter readings during one dress rehearsal; memorized the basic exposure setting and then remembered whether the light went up or down and by how much - 1/2 stop or a full stop - and shot about 11-13 rolls of 36 exposure Tri-X before and during the play.

    Too many people get overwhelmed with the "techniques" of photography - something necessary at times - but then don't work to simply matters - at least in their head - and often forget the most important aspect - aesthetics.

    Talk with you later,

    Bill
     
  7. Avis

    Avis TPF Noob!

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    I always thought that 'LV' stood for 'Luncheon Vouchers'. You learn something new every day.
     
  8. selmerdave

    selmerdave TPF Noob!

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    Absolutely. Take care.

    Dave
     

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