May I know where should QRC-40B be use for? I just want to make sure it will not needed before I order M2 package.
for M2, it stacks (in parallel or perpendicular) with QRC-40A to allow you to slide along a rail. Good if you use very short wide angle lens (eg. fisheye) lens as well as long lens. This avoid rail getting into the image when very short wide angle lens is used. It also slide the tele lens with collar to center of gravity or NPP. It is good for marco photography.
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