I am considering the use of CPF with Ringflash for macro to reduce reflections on curved shiny subjects. Small curved surfaces like dimples result in numerous tiny reflections which some may call hotspots.
How would I adjust the CPF to optimum without using the light of the ringflash? If adjusted by trial and error, would the chosen setting suit most subjects. Plan B is to buy a cheap CPF and "suck it and see", as the great Mo Macacie would say.