Hi everyone! I have a D90 and a Metz 50 AF-1. I'm using the flash as a remote slave and, through the commander panel in the camera, I set Group A, Channel 1 to TTL and the built-in flash to off ("--" according to Nikon). I set the Metz to remote slave, Group A, Channel 1. However, when I take a photo, if I don't extract the built-in flash from the camera, the Metz does not fire. If I extract the built-in flash, then both flashes fire. Is this normal? I mean, I switched the internal flash to off, why does it fire? It actually fires so weakly that not a trace of it can be seen in the picture. However, I thought the communication between camera and flash happened through IR, not visible light. Note: I did NOT set the Metz to Servo. It is simply remote slave. A proof of that is that the Metz does not let me choose "Manual" mode when I set it to slave, as it expects such decision to come from the camera. Also: if I use exposure compensation for Group A from the camera, the Metz actually does it. There is no doubt the camera and the flash are communicating digitally, but why would the built in flash fire??? Thanks everyone!