I have the 603s and have used them with two different Nikon APS-C cameras and a Nikon full-frame (the D800). It was only the D800 that had a shutter lag problem and needed to be used at 1/150s. I posted this on another site and someone said they had a similar problem with Canons -- the APS-C cameras had no problem, but the full-frame Canon did. That is a pretty scant base of data to extrapolate from, but it is interesting. Have other people had delay problems with the 603s? Have they been on full-frame or DX cameras?