>Am I correct that I do not lose TTL-BL when shooting with the >head pointed 45 degrees and the white card pulled out? I >tried it and was pleased with the result. Then again, TTL-BL >with the flash head pointed directly was nice too but only >with the diffuser attached. > >I also applied -1.7 flash comp.
TTL-BL works best if you do not tilt the head.
The reason for this is that when the flash head is pointed directly at the subject, distance to the subject (as reported by the D lens) is used as the primary input to the BL calculations to determine the correct flash power.
If you tilt the head (or use a non-D lens), the system reverts to the monitor preflash to determine the correct flash power, but that doesn't work very well when in bright daylight. Of course, TTL-BL should only be used in bright ambient conditions and the camera meter must be centered. Most pros shoot TTL-BL fill shots using camera P mode to be sure the meter is always centered.
Most of the time, you don't have to worry about diffusing the light when using TTL-BL mode, because you are only adding a small amount of fill, and diffusing doesn't change the image noticeably.