About how many passes in cycles does it take until the grain level doesn’t change? I’ll go into 1000 passes and somewhere mid-way or so, the level of grain remains about the same. Seeing as my GPU doesn’t work with Cycles (.1 less) it takes longer for me to render in cycles so I’m looking for the least number of passes I can do before it’s all good.
It really depends on what kind of materials you use in your scene and the number of lights
My own guessing, if it still have moderate noise after 4000 samples better to do something, or it take weeks to converge. In theory noise level decreasing speed ~ SQRT(Number of samples) with Montecarlo integrators, fast at beginning but slower and slower after that. Cycles use tricks that relax that rule (Sobol low discrepancy quasi random), but that another story.