Convert camera meter to incident meter?

Discussion in 'Photography' started by Martin, Oct 2, 2005.

  1. Martin

    Colin D Guest


    I'll ignore your snide remark about rabbits - I should just tell you to
    go to hell - but I'll give it one more shot. After this, boyo, you're
    on your own.

    Suppose the sun is lighting the place up with 100 lumens of light
    (whether that's actual or not doesn't matter here). Ok, with 100 lumens
    lighting up an 18% gray card, guess how many lumens will be reflected
    *from* the card? Yep, you guessed it, 18. So you point a
    *reflected-light* meter at the card, and it gives an exposure of, say,
    1/125 at f/16. The reflected light meter is *calibrated* to give that
    reading from an average reflectance subject.

    Now, you point an *incident-reading* meter at the light source, the sun
    (we're presuming here that the subject is front-lit). The incident
    meter sees 100 lumens, and will indicate an exposure of 1/125 at f/16,
    because it's calibrated to do that.

    If your meters don't give the same answer within, say, a 1/2 stop, then
    1) either the meter or meters are out of calibration, or 2) you are
    using them wrongly. End of story.

    NewsFlash: I just looked at your website on modifying the Ranger 9 to
    use silver oxide batteries. My opinion is that you have tampered with
    the meter, that your measuring technique of reflected versus incident is
    probably ok, but the Weston meter is all to hell with its calibration.

    My advice is to get it professionally calibrated and then try your tests

    You might have told the collective would-be helpers in this thread that
    you did this to the meter, instead of letting us all waste our time
    trying to help you, assuming the meters were in calibration. All bets
    are off till you get it calibrated.

    I'll leave it here in case I say something I might regret.

    Colin D.
    Colin D, Oct 7, 2005
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