>It didn't appear that the Flash mode wasn't TTl, without the >BL. That's what I meant by "it didn't work". >Referring to setting the mode on the flash only and not >setting Metering mode on the camera. > >I thought they talked to each other (with the SB800) in the >hot shoe. And that setting parameters on one or the other, >limited parameters on the other. In other words, Matrix >wouldn't be allowed when in TTl mode. And, correspondingly, >TTl-bl wouldn't be allowed if camera metering were to set on >Center or Spot.
I think it helps to be able to reason this out:
TTL-BL mode requires a large portion of the frame to be metered by the camera so it can figure out how much ambient light there is, so it can balance brightness of the subject with it.
There are two metering modes that meter a large portion of the frame: Matrix and Center Weighted.
Consequently those are the two modes that will allow TTL-BL mode to work.
Regular TTL mode doesn't use any metering information from the camera, so regular TTL can be selected on the flash in any camera metering mode: Spot, Center-Weighted, or Matrix. That's why you can select regular TTL in any of the camera metering modes. The camera metering modes only affect the ambient contribution to the image. They have no effect on the power of the regular TTL flash. The regular TTL power is set entirely by the monitor preflash.