True or false: sunlight = sunlight

Discussion in 'Exposure Discussion' started by David Lyga, Apr 28, 2013.

  1. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Assume midday, with unrestricted sunlight. In neither case is the actual sun obscured by clouds. Now take these two scenarios:

    1) Scene fully lit under completely blue sky

    2) Scene fully lit under sky with many white clouds (but, again, sun, itself, is not obscured by clouds)

    Do the scenes require the SAME exposure or does the scene with the completely blue sky demand one stop more exposure? I think that the 'blue sky' scene does require more exposure because there is no benefit of the white clouds 'filling' in with more light. And, there are (British) photo books that attest to my assumption.

    Agree or refute: I do not bite. - David Lyga
     
  2. HTF III

    HTF III Member

    Messages:
    133
    Joined:
    Apr 18, 2013
    Shooter:
    Multi Format
    I'd need a light meter and an appropriate day to contest that. Today it is cloudy, bleak, a little cold, and miserable out there. April 28, and hasn't felt like spring yet.
     
  3. Bill Burk

    Bill Burk Subscriber

    Messages:
    4,984
    Joined:
    Feb 9, 2010
    Shooter:
    4x5 Format
    Agree, the white clouds add fill light to scene 2.

    Not only because the entire scene may be "brighter"... but the illumination in the shadows themselves will be lifted by the clouds.
     
  4. HTF III

    HTF III Member

    Messages:
    133
    Joined:
    Apr 18, 2013
    Shooter:
    Multi Format
    But a whole stop??
     
  5. Bill Burk

    Bill Burk Subscriber

    Messages:
    4,984
    Joined:
    Feb 9, 2010
    Shooter:
    4x5 Format
    Sure.

    Think of scene 1 as Sunny-16 and scene 2 like snow/sand... can be f/22
     
  6. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    But, Bill, if we do not take shadows into consideration, I still maintain that the SUNLIT parts are brighter with the white clouds. And I am not the only one to believe that.

    Yes, HTF, a whole stop.

    This is a situation that is rarely discussed, but appropriately relevant. - David Lyga
     
  7. MattKing

    MattKing Subscriber

    Messages:
    16,820
    Joined:
    Apr 24, 2005
    Location:
    Delta, BC, Canada
    Shooter:
    Multi Format
    The shadows are critical when you are determining exposure of negative films.

    More diffusing and reflecting clouds means more light in the shadows.

    The suggestions that David refers to don't really apply to transparencies (or digital).
     
  8. Doremus Scudder

    Doremus Scudder Member

    Messages:
    1,276
    Joined:
    Sep 10, 2002
    Location:
    Oregon and Austria
    Shooter:
    4x5 Format
    I'd think that the clouds would fill the shadows a bit, making the total subject brightness range less. If you base your exposure on the shadows, then scenario 1, complete blue sky, would likely be more exposure and less development. The same scene with lots of white clouds filling in the shadows would be less exposure but likely a bit more development. I think I end up with N-1 in the first case a lot more than in the second, especially if I'm using any blue-subtracting filters.

    Best,

    Doremus
     
  9. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Roll film does not allow N-1 (unless the scenes are the same type). Thus, Ansel Adams does not come to the rescue here.

    Try to forget shadows here: we all know that fill light lightens them. I am talking about the SUNLIT portions of the scene and to simplify, let's focus upon ONLY a grey scale fully lit by sun. Would exposures in either case be identical or different. I think different. - David Lyga
     
  10. cliveh

    cliveh Subscriber

    Messages:
    4,711
    Joined:
    Oct 9, 2010
    Shooter:
    35mm RF
    For my money there would be no difference in exposure. In both cases (if I'm reading it correctly), the scene (that to be photographed) is lit by full sun, so if the surrounding illumination is blue sky or diffuse, it would have little influence over direct sunlight.
     
  11. kintatsu

    kintatsu Member

    Messages:
    368
    Joined:
    May 1, 2012
    Location:
    Bavaria, Ger
    Shooter:
    4x5 Format
    I would imagine that the same amount of light would be falling on both, as they are directly lit by the sun. Giving panchromatic b emulsion as the film, the exposure should stay the same, perhaps up to 1/3 less. That is entirely without taking into account the actual values.

    I have found that in similar cases, the sunlit values don't change much. It's when filters and other values within the scene are accounted for, there can be quite a difference.
     
  12. HTF III

    HTF III Member

    Messages:
    133
    Joined:
    Apr 18, 2013
    Shooter:
    Multi Format
    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?
     
  13. baachitraka

    baachitraka Subscriber

    Messages:
    2,316
    Joined:
    Apr 6, 2011
    Location:
    Bremen, Germany.
    Shooter:
    Multi Format
    When I incident meter(loosly BTZS for roll film) I may prefer to have scene 2 every where.
     
  14. Sponsored Ad
  15. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    It is admittedly difficult to test this definitively: one would have to wait days on end for the perfect situation. I think that the masterful Focal Encyclopedia of Photography parses this issue though and agrees with what I have inferred.

    Like others here, I originally thought that an 'elegant' answer such as 'it is still lit by the same light' would trump all because of the logic that it seems to rest upon, but there really might be a difference. We'll wait for more replies to this simple but confusing quandary.

    I will not be at another computer until Monday. - David Lyga
     
  16. Bill Burk

    Bill Burk Subscriber

    Messages:
    4,984
    Joined:
    Feb 9, 2010
    Shooter:
    4x5 Format
  17. Bill Burk

    Bill Burk Subscriber

    Messages:
    4,984
    Joined:
    Feb 9, 2010
    Shooter:
    4x5 Format
    We wait days on end for this situation anyway... Beautiful light.
     
  18. HTF III

    HTF III Member

    Messages:
    133
    Joined:
    Apr 18, 2013
    Shooter:
    Multi Format
    Thanks Bill. I mean on the moon in 1969. EVERYTHING was a chance and a risk then. Can you imagine the wonder and worry in the minds of all the NASA people then? I'm betting they used Sunny f/16 on the side of the LEM facing the sun. How could they really know?
     
  19. bernard_L

    bernard_L Subscriber

    Messages:
    414
    Joined:
    Feb 17, 2008
    Shooter:
    35mm
    @ David. Agree. But definitely by not one full stop. That (1 full stop) would be the case if the clouds had only forward scattering; then they would distribute on the ground a flux equal to the incoming solar flux. But as we know from air travel, clouds also reflect a lot of sunlight towards deep space. Which can be confirmed without flying: under a cloud cover the light flux is less than under direct sun. Closer to 1/4 (2 stops from sunny 16). So, in the most favorable case (under a small clear hole in a sky otherwise covered with nice white cumulus) one might hope for 1+1/4=1.25=+1/3stop; rough, quick estimate.

    @ other readers. If you don't agree, I won't go into one of those sterile forum controversies; just use your light meter under comparable conditions (same period of year + same daytime = same sun elevation).

    Measurement worth thousand theories. Confucius. (or, was it Galileo? or Groucho?)
     
  20. ntenny

    ntenny Member

    Messages:
    2,283
    Joined:
    Mar 5, 2008
    Location:
    San Diego, C
    Shooter:
    Multi Format
    In the last analysis I think it varies from scene to scene. Certainly cloud cover can reflect light---city skyglow on a cloudy night will attest to that---but there are so many variables that I would be greatly surprised to find a usable general rule (other than "when in doubt, meter").

    -NT
     
  21. Bill Burk

    Bill Burk Subscriber

    Messages:
    4,984
    Joined:
    Feb 9, 2010
    Shooter:
    4x5 Format
    Yesterday, out on the dressage court with my sister-in-law Patience, I was a stop over Sunny-16. No clouds. This was light sand, so reflecting up to the subject.

    Same light, different scene, the ranch house, no sand. I felt that the shaded side of the building had to be at least Zone IV, so I gave more exposure. The white pickup truck in full sun will be a challenge to print.

    Will have to wait until the clouds come out to test bernard_L's theory. For now, it's a sunny day with blue skies...
     
    Last edited by a moderator: Apr 28, 2013
  22. pentaxuser

    pentaxuser Subscriber

    Messages:
    8,202
    Joined:
    May 9, 2005
    Location:
    Daventry, No
    Shooter:
    35mm
    Is there a minimum percentage of the sky that has to be filled with white clouds to make a difference and might it depend on latitude and time of year? Even in high summer here in the U.K. and around noon shadows can tend to be soft even in an unbroken blue sky.

    pentaxuser
     
  23. benjiboy

    benjiboy Subscriber

    Messages:
    8,538
    Joined:
    Apr 18, 2005
    Location:
    U.K.
    Shooter:
    Multi Format
    That's why God invented light meters.
     
  24. fotch

    fotch Member

    Messages:
    4,824
    Joined:
    Mar 16, 2005
    Location:
    SE WI- USA
    Shooter:
    Multi Format
    :laugh::laugh::laugh:
     
  25. Fred Aspen

    Fred Aspen Member

    Messages:
    715
    Joined:
    Aug 23, 2006
    Location:
    North-ish-western US
    Shooter:
    Multi Format
    I find it hard to believe that the contribution of the reflected light by the white clouds would be a stop brighter. When I think about the intensity of the light from the white clouds compared to unobstructed sunlight, it has to pale in comparison. Therefore, I refute your hypothesis.

    Edit: Actually, I have done this. Near noon I have taken incident readings with a completely blue sky. On successive days I have taken incident readings with lots of puffy white clouds but not obstructing the sun. The readings were virtually the same; the worst case was perhaps down by 1/6 stop (most likely water vapor in atmosphere). (my secondary hobby is collecting/testing light meters.)
     
    Last edited by a moderator: Apr 28, 2013
  26. Ian Grant

    Ian Grant Subscriber

    Messages:
    18,038
    Joined:
    Aug 2, 2004
    Location:
    West Midland
    Shooter:
    Multi Format
    Interesting, when I shoot in Turkey/Greece my meter's near maximum when it's blue sky (the norm most of the year), and a few clouds drop this because there's normally some atmospheric haze.

    I definite don't need to stop down or use a faster shutter speed when there's clouds.

    Ian