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  1. #31
    David Lyga's Avatar
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    Well, the amount of change in intensity might well be off.

    Actually this discussion might be at least somewhat analogous to a situation whereby flash exposure depends upon the reflectance of surroundings. Take, for example, the following: you wish to photograph a grey scale that is exactly 10 feet from the camera. The environment is in complete darkness. With flash on manual, you judge the proper aperture and fire. Now, if you are in a small room that has white walls and white ceiling, you are going to get a different rendition of the grey scale than if you were outside, at night in an open field with nothing to reflect upon. The grey scale in that outdoor instance would be considerably underexposed.

    The following attachment shows part of page 416 of my (desk edition) FOCAL Encyclopedia of Photography under the category of 'exposure'. - David Lyga
    Attached Thumbnails Attached Thumbnails sunlight APUG.JPG  
    Last edited by David Lyga; 04-29-2013 at 07:47 AM. Click to view previous post history.

  2. #32
    benjiboy's Avatar
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    Quote Originally Posted by Chan Tran View Post
    God didn't! You can't blame God for just about everything.
    Why not Chan, a few years ago a recently constructed ultra modern local church blew down in a severe winter storm and when the church commissioners tried to claim from their insurance company they refused the claim on the grounds that it was excluded under the exclusion clause "war, civil disobedience, and acts of God".
    Ben

  3. #33

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    Quote Originally Posted by JBrunner View Post
    Just overexposed two stops, and call it bullet proof.
    same here

    Quote Originally Posted by HTF III View Post
    Not to sidetrack the discussion--but I always wondered how NASA pre-planned exposure for the astronauts. The sky on the moon was black. Did they use Sunny f/16?
    didn't you see the movie "capricorn 1" starring orenthal james simpson
    even though that was about mars it was based on the hidden truth behind the lunar landings.
    http://en.wikipedia.org/wiki/Apollo_...iracy_theories



    Quote Originally Posted by Bill Burk View Post
    They followed instructions like these...

    http://www.apug.org/forums/showthrea...ferrerid=38808

    i keep forgetting about time travel

    thanks bill

    john
    john

  4. #34
    Bill Burk's Avatar
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    Quote Originally Posted by David Lyga View Post
    Well, the amount of change in intensity might well be off.

    Actually this discussion might be at least somewhat analogous to a situation whereby flash exposure depends upon the reflectance of surroundings. Take, for example, the following: you wish to photograph a grey scale that is exactly 10 feet from the camera. The environment is in complete darkness. With flash on manual, you judge the proper aperture and fire. Now, if you are in a small room that has white walls and white ceiling, you are going to get a different rendition of the grey scale than if you were outside, at night in an open field with nothing to reflect upon. The grey scale in that outdoor instance would be considerably underexposed.

    The following attachment shows part of page 416 of my (desk edition) FOCAL Encyclopedia of Photography under the category of 'exposure'. - David Lyga
    Aha, "Lightening the shadows". That's the main reason.

  5. #35

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    Quote Originally Posted by David Lyga View Post
    Well, the amount of change in intensity might well be off.

    Actually this discussion might be at least somewhat analogous to a situation whereby flash exposure depends upon the reflectance of surroundings. Take, for example, the following: you wish to photograph a grey scale that is exactly 10 feet from the camera. The environment is in complete darkness. With flash on manual, you judge the proper aperture and fire. Now, if you are in a small room that has white walls and white ceiling, you are going to get a different rendition of the grey scale than if you were outside, at night in an open field with nothing to reflect upon. The grey scale in that outdoor instance would be considerably underexposed.

    The following attachment shows part of page 416 of my (desk edition) FOCAL Encyclopedia of Photography under the category of 'exposure'. - David Lyga
    Hi David,

    Yes, this is fairly self-evident. One factor that you haven't touched on is that the spectral composition of sunlight is also influenced by Rayleigh scattering of light, and the frequency affected by scattering depends on the particle size of the matter doing the scattering. The blue colour of the open sky is caused by light scattering by oxygen and nitrogen molecules. We are actually seeing the light scattered away from the direction it is moving in. In early or late hours, the distance the light travels through air is sufficient to deplete the blue spectrum enough to turn the light substantially yellow, hence the "golden hour". Golden hour is not quite relevant to your discussion, but it is worth noting that latitude has a marked effect on spectral composition for the same reason. Smoke, dust and mist in the higher layers of the atmosphere may have similar effects on spectral composition, and may vary due to changes in weather, volcanic erruptions, seasons etc. All things considered, "Sunny-16" is a guideline with a narrow set of parameters, and probably never was intended as a rule or a law.

  6. #36
    Stephen Benskin's Avatar
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    ANSI - Exposure Guide's first adjustment for clouds is with a haze over the sun. That was basically the same thing I found in Jones' paper (which the standard was based). It appears that an unobscured sun with or without clouds surrouding it has approximately the same illuminance.

    BTW, the ISO speed standard's color temperature exposure changed in 1960 from skylight to daylight. This prompted a small change in the proposed speed constant (adjust for slower resulting speeds).

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