Hi. Just wondering about this. I suppose investing in an SU-800 or something would resolve this. But I don't really want to because the pop-up flash does the job fine for triggering flashes remotely. From my understanding, whilst the flashes are "visible", the remote control is done via infrared light so it should be possible to block the normal visible spectrum light whilst still letting the IR passthrough to trigger remote CLS flashes. Does anyone out there make such a clip on filter?