I am an amateur photographer doing mostly travel and landscape photos. This week I upgraded from a D300 to a D750. I am very excited about the new camera. Before I had much chance to use it, I was asked to do a large group photo. I have taken the same photo every year using my D300 and two speed lights? I should have used the D300 for the shoot since I had not had much chance to use the D750. Dummy me, I took the D750 and things did not go smoothly. My set up was the D750 in commander mode with the on board flash not firing but opened, and two off camera flashes on my left and right. A SB600 was on my left and a SB910 on my right. Both speed lights were in wireless mode but the SB 910 would not fire. I changed batteries and moved the flashes around a bit bit the 910 would still not fire. Unlike previous photos of the group, this one was done outside while previously all of the photos were done indoors. I had tested the set up at home before heading out and everything was working before I left. I did find that the 910 would fire if I faced it directly with the D750 so I am wondering if this was a camera issue or if the commander mode on the camera and the flash just could not see each other in the outdoor environment. This was an open area in a parking lot without any walls or bounce surfaces. Thanks in advance for any help.