The new Seven5 filter holder has been designed as a cheaper and improved replacement for the RF75 for use on all small cameras, CSC, M4/3 and any system where the lenses have a max thread size of 72mm.
The RF75 was originally designed for, and still has a use on fully rangefinder cameras, where through the lens viewing is not possible and accurate filter positioning is not easy. On these cameras, the clear increments on the RF75 will allow accurate and consistent use of filters.
All 75mm filters, adaptor rings, lenshoods etc. are fully compatible with both filter holders.
The 75mm Big Stopper has been designed to work with the Seven5 holder, but in tests it appears to work well with the RF75 holder as well. Used normally, the 75mm Big Stopper should work in your RF holder without problem, but we cannot guarantee it.