• 2007-05-21

    + 白平衡:茅塞顿开

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    http://www.blogbus.com/newswolf-logs/5449296.html

    Balancing Flash with Tungsten Light

     

     

     

    Your typical indoor wedding reception is nearly inevitably lit by tungsten light. And because the lighting is as nearly inevitably fairly dim, this then forces us to use additional lighting – which most often is on-camera flash.

    Since the light levels are low, and we use flash for the foreground, our backgrounds tend to go darker, as in this image on the right.

    This generally does not look pleasing, and it could look a lot better.

     

     

     
     

    There are several ways around this.

    • use additional lighting.

    We could use additional strobes around the reception room, to lift the general light levels.

    Here for example is how you could place the additional strobes.

     

     

    And this next image show how the images would typically look - with even light from foreground to background.

    For this image, my settings were 1/100 th @ f2,8 @ 100 ISO.

    My on-camera flash was dialed down to -0.7 stops flash exposure compensation,

    Since I was using two Q-flashes on light stands bouncing light into the curved ceiling. This flooded the room with light.

    But it might not always be feasible to use additional lights. Sometimes the shape and size of the venue, and the height of the ceiling (too low or too high) makes it difficult. And sometimes it just isn’t possible to use the additional lights … or it could be an artistic decision to have a different look to the lighting.

     

     
     


    Then we have another option:

    • use a slower shutter speed, and allow more ambient light in.

    This will give us a more gradual light fall-off to the background. As a result we will have more detail in the background and more context. We’ll see the environment we were photographing.

    But this slower shutter speed gives us other problems which we have to juggle.

    The first consideration is how much subject movement and blur we’d find acceptable .. and more importantly, what our clients would be happy with. If subject motion is a problem, then we might very well be best off using additional lights. Flash will stop the action.

    But there is an additional problem – that of a white balance mismatch between flash and the available (tungsten) lighting.

    The colour temperature of the small strobe units is around 54oo K .. which, if the actual number has little meaning to you, means that it looks a lot cooler than the tungsten / incandescent light does. That warm glow of tungsten light (which varies a lot around 3ooo K), makes the flash appear too cold, or too blue. The converse of this means that if you adjust your white balance so that the flash appears neutral, your background goes murkily orange. It is this disparate WB that causes the background to get that grungy tone when you use flash with tungsten / incandescent light.

    In this image, I dragged my shutter to 1/20 th second to allow more light in from the background.

    (Camera settings, 1/20 th @ f4.0 @ 500 ISO)

    As an aside, the reason why you’re not seeing camera shake there, or any orange colour cast on his face, is that he was standing with his back to the ambient light source, and was mainly lit by bounce flash.

    But that orange colour cast in the background doesn’t look that pleasing.

    Here’s an example of how messy it can look if you mix flash with tungsten light in about equal quantities. (And yes, sadly I was the perpetrator here). (Wolf's note:下面就是两种色温的光掺杂在一起的惨状,也是我经常拍片出现的效果,Thank goodness现在找到症结了。)

    We can get reduce it by filtering our flash, and bringing the strobe’s white balance closer to that of the available light.

    From the same wedding, where I immediately changed over to another strobe that was gelled for Tungsten light. I also changed my camera’s WB setting to Tungsten.

    (The gel in this case was the one that comes with the Nikon SB-800 strobe)这回就对了

    And for easier comparison, here are two images which are exactly the same, except for how the flash was gelled with a filter, and the WB changed:

    In this final image in this sequence, the couple is mostly lit by filtered flash, and the bridal party in the background is mostly lit by the tungsten light in the church.

    More specifically - we can filter our strobe in various ways:

    • CTO gel to bring WB down to 29oo’ K
      (might be difficult to get full range of colours)
    • other CTO values for different K values
      ½ CTO converts flash to 38oo’ K
    • CTS filter (less red) brings WB down to 29oo’ K
    • ½ CTS converts flash to ‘38oo’ K
    • gel supplied with Nikon strobes, WB to Tungsten
    • gold Stofen ~ 38oo’ K

    The gold Stofen is a good compromise in that it still leaves the background warm.
    My preference lately is for the gold Stofen, for exactly that reason. (用3000K万全匹配的gel胶可能看起来白得太正,所以用金色Stofen罩子,就是我最先贴图的那个,3800K,可使画面略黄,保留一点气氛)

    Where it helps to gel the flash is where you have to deal with strong light from the videographer.

    In this sequence of images, I had to contend with the tungsten light in the temple, as well as the light from the videographer that intermittently brightened up the subjects with his video-light (which is an Incandescent / Tungsten light source)

     

     
     

    My settings for this sequence were:

    1/125 th @ f4 @ 800 ISO .. which is a fairly high shutter speed for low light.

    But this was mostly a decision forced on me by the bright video-light.

     

    With the gold Stofen on my flash, it was then much easier to find a pleasant WB where the skin tones looked good. And using gelled flash made the light more even on the subjects, that if I had relied more on the erratic video lighting.


     

     

    Controlling the amount of ambient light for effect :

    I photographed a sequence of images of this bride standing in the doorway of the bedroom on the
    2 nd floor. The light behind her was from a Q-flash on the 1 st floor bouncing upwards into the stairwell at 1/8 th power. The blue background is a painted mural in the landing.

    In the first image, my settings were: 1/40 th @ f2.8 @ 400 ISO

    For the 2 nd image, I changed my shutter speed to 1/100 th

    That slow shutter speed was chosen specifically to allow that touch of warmth from a bedside lamp in the bedroom that was casting a glow inside the room. But for the 2 nd image I chose a higher shutter speed for a slightly more silhouette effect – by reducing the amount of ambient light that registers in the image.

     

    Using the warmth of Tungsten lighting :

    In this image however, I specifically did want that warm orangey glow in the background, since it is fitting here. The Christmas lights need to be a warm colour. Therefore I didn’t use a gel to change the WB of the image.

    Since the couple was in the “shade” of the available light, they would’ve been completely silhouetted. But I bounced flash off the side of the building to light them. So my WB here was originally Daylight WB (to offset the warm-white tone of the building’s wall), and then touched up in RAW processing afterwards.

     

     

    And finally, using Tungsten lighting without flash :

    Sometimes the available Tungsten light has a quality that need not be changed.

     

     
     

    原文来自:http://www.planetneil.com/faq/flash-with-tungsten.html

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    评论

  • Hi, Gang, congratulations!! I really like your blog (Annie told me about it, though she's not sure where you are). How about dropping me a line or calling me when you're free? My cell is 319-594-6768. Take care:-)

  • hh,高心并表示庆贺。
  • 嗬嗬,我终于把相机买来了。现在读你的技术文章,会更有感觉了。不过,好长的文章啊 :p
    GT News回复dena说:
    好,這么快就搞定了。買的啥機器啊?多半是老公決定資助一步到位了吧。

    上面的文章其實看著長,實際也就是七八張圖片的長度,一目了然的東西,如果口述,很快的。

    不過建議Dena還是先熟悉熟悉機器,對光圈、快門、ISO、曝光、白平衡有點感性認識以後再來看這篇文章,不然你會五里云霧的。
    2007-05-22 07:58:17
  • Thanks for mentioning me... xixi~



    And, woooow! What a nice article and I have so much to learn about photography!!!



    You are amazing!
    GT News回复Joyce说:
    就知道你是聰明好學的好孩子,好東西當然要同你分享了。
    2007-05-22 07:57:02