I've been adding sodium sulfite to dilutions of Rodinal as follows:(posted 8326 days ago)For a 1:100 dilution, I mix 300ml water with 30grms(4tsp.) of sulfite and add 3ml of Rodinal. This is a 10% solution. I usually follow Agfa's recommended time/temps and adjust from there. I know this is a lot more than most people recommend, but, it works. You can see that the grain in a film like APX400 becomes finer with a grain focuser. Unfortunately, this will not make the grain disappear, so don't expect ss to work miracles, or anything else either! Another observation I have is that there is really minimal effect on sharpness when ss is added. Rodinal at high dilutions is extremely sharp. The problem as I see it is that Rodinal may not be a good choice of a developer for 35mm fast films at any dilution with any additive. The price for sharpness is grain, albeit, very nice grain. With slow films, Rodinal is king, and, with larger formats than 35mm, wow!
Jeff