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  1. #11
    Ed Sukach's Avatar
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    The "EV" - Exposure Value - is independent of film speed. It indicates a combination that will allow a specific amount of light to pass. If you are familiar with reciprocity (n.b. NOT "reciprocity FAILURE"), an exposure of 1 second @ f/22 will allow the same amount of light to pass as an exposure of 1/60 second @ f/2.8 - both -- I'll check the Hasselblad lens scales -- have the same "EV" - 9. 1/60 second @ f/5.6; 1/8 second @ f/8; 1/4 second @ f/ 11 ... All allow the same amount of light - and all are EV 9.

    The sensitivity of an exposure meter is represented by the lowest and highest EVs it can read at a given film speed; therefore, @ ISO 100 - a given meter may be capable of reading EV 2 - 2 seconds @ f/2.8; to EV 18 - 1/500 second @ f/22.
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #12
    Helen B's Avatar
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    "The sensitivity of an exposure meter is represented by the lowest and highest EVs it can read at a given film speed; therefore, @ ISO 100 - a given meter may be capable of reading EV 2 - 2 seconds @ f/2.8; to EV 18 - 1/500 second @ f/22."

    Unless it is the meter in a TTL camera that reads at the working aperture, which is what this thread is all about...

    Best,
    Helen

  3. #13
    Ed Sukach's Avatar
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    As I understood it - and I HAVE re-read, the question was "What does EV (Exposure Value) Mean?" It was framed as, "I see the sensitivity of exposure meters given as 'X' EV at a certain ISO".
    EV alone does not define sensitivity, or the method of metering, or have anything to do with film speed. One could easily substitute, "This meter has the capability of measuring the amount of light ranging from that requiring an exposure of 1 second @ f/2.8, given a film speed of ISO 100, to that amount of light requiring an exposure of 1/500 second @ f/22, given the same film speed of ISO 100."
    It is more economical - takes up less space in the brochure - and is widely accepted, to give the sensitivity as "EV3 - 18 @ ISO 100".


    I think it is of great usefulness to keep our terms and definitions straight: It does no good to confuse "f/stop" with "Effective f/stop", or the much more utilitarian term "T/stop".
    Carpe erratum!!

    Ed Sukach, FFP.

  4. #14
    Lee L's Avatar
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    Ed,

    That was the original question, but that turned into "why won't my Bessa R meter at settings that are within the specified meter sensitivity range in EV?". This is the question that Helen has answered completely and accurately.

    Helen's point is that the statement of a pure EV sensitivity range isn't a complete statement of the metering capacity of this particular camera, and that it actually can't meter at all combinations of ISO/aperture/shutter speed that fall within the stated EV sensitivity range. That failure to meet the stated standards is a function of stopped down TTL metering.

    Lee

  5. #15
    Ed Sukach's Avatar
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    Ah! I've been "hoist on the petard" of the shifting topic.

    I apologize .. in my zeal to clarify, I must have come on as an an unconscionable know-it-all, which I assure you, I DON'T.

    In a different life I used to work in a place making sophisticated, and I mean sophisticated custom optical systems. One of my tasks was calibrating "light meters" - mostly Cascade Photomutiplier types ... so topics bordering on that subject tend to fire zealous neurons. Possibly those neurons were sensitized from a few accidental zots from photomultiplier primary power supply circuits. Real eye-openers!

    The history of the means of controlling the amount of light - the exposure of film - and why we call varying sized apertures - whether produced by individual holes or sliding blades - "stops" is in itself fascinating.
    Carpe erratum!!

    Ed Sukach, FFP.

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