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  1. #21

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    Quote Originally Posted by Maris View Post
    Here are some approximate numbers.

    Direct sunlight at midday is pretty exactly 120 000 Lux. Exposing film to this intensity for 180 seconds will result in 21 600 000 Lux.seconds of exposure. This is enormously greater than the 0.1 Lux.seconds a 100 ISO film gets in camera; more than 200 million times greater!
    ca. 27.7 stops more ?

  2. #22

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    You're still ignoring the bit mentioned earlier, that the Lux numbers are a measure for how much light is falling on the scene. It is a measure, not for what a lens (and the film behind) it sees, but of the maximum amount it could see.

    A lens always projects light that is reflected off something in that scene (unless you point the lens at the light source itself, and have it fill the lens' entire field of view).
    And unless that bit the lens sees reflects all the light that is falling on it, and does so - as far as the field of view of the lens (and the film behind it) is concerned - without concentrating or dispersing the light, it is not the same amount.

    The relation between incident and relected light (the latter being what the lens, and the film, get to see) depends on unknowns. You can't derive a ' Lux level' at film plane, just taking the 'Lux level' in the scene as measure.

    And that is still ignoring what a lens does, assuming instead that all it does is relay all of the light to the film.

  3. #23

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    Quote Originally Posted by Q.G. View Post
    You're still ignoring the bit mentioned earlier, that the Lux numbers are a measure for how much light is falling on the scene...
    And that is still ignoring what a lens does, assuming instead that all it does is relay all of the light to the film.
    Thank you for the signposts...
    I will do a reality check on it once I get the numbers ostensibly "working".

    Ray

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