Thanks for this answer. The MB air has to firewire connexion, only thunderbolt. So I have first to use a thunderbolt to fw adapter, then if I plug my back to it with no power supply, it turns on but I can't shoot anything, if I shoot, the P65+ turns off and restart. I have a lindy firewire repeater/hub with a 2A/12v power adapter, it works fine but not on X and P mode of the 645DF+. It is fine with the Av mode and M mode. This in tethered mode. If I only use the repeater with its 12v/2A adapter not connected to the macbook air, so olnly as a power supply for the back, it works fine, on compact flash image storage. If I connect the repeater to the mbook air via the thunderbolt adapter, it doesn't work in X or M mode (the back turns on but turns off and restart if I shoot in X or M mode). No matter C1 is launched or not. So, as I saw that the power adapter (wall adapter ?) provided by Unibrain is a 12V/3A adapter, I suppose my issue comes from the fact that my power adapter is too weak. I'll try with a 3A adapter. I bought this repeater 3 weeks ago, If I knew those issue I would have prefered to buy a Unibrain repeater... I confirm my Phase One dealer told me there was no possibility to power supply a P65+ with a MB air (except with batteries of course), and the Leaf dealer told me that the leaf repeater may not fit for P65+ backs as voltage is not the same... A bit of a confusion there !