One of our readers, Desmond, is a curious person. He found out through his tests that some of the common understandings of the Nikon TTL/BL flash mode may not be accurate and some facts even appear to contradict the voice of an expert. For example, Russ said that “… TTL-BL does not work correctly when the background is darker than the subject.” However the tests from Desmond showed it worked just fine.
You can read the complete tests results and his conclusions at his blog or watch the following Youtube video for his demonstration.
At beginning, I was a little skeptical. However the test results are pretty hard to dispute. Perhaps the conclusions are wrong but there has to be a better explanation of the results.
We should all blame Nikon who never seems to have come out with a clear technical explanation of how the Creative Lighting System (CLS) including TTL-BL mode works. What Nikon tells us is the typical nebulous description such as “…Balanced Fill-Flash is performed. The flash output level is automatically adjusted for a well-balanced exposure of the main subject and background.” (SB-800 Instruction Manual).
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Keywords: Balanced Fill Flash, CLS, Creative Lighting System, Fill Flash, Flash photography, Flash photography, Nikon, TTL-BL, TTL/BL