There is a way to add ascorbate to Rodinal working solution that seems to give somewhat finer grain without disturbing its other characteristics. This is described in www.unblinkingeye.com somewhere. Briefly, mix 1 teaspoon ascorbic acid powder with 1/2 teaspoon sodium bicarbonate in a small amount of water. When effervescence ceases, add 20 ml Rodinal concentrate and water to 1 liter. Treat the mixture as 1:25 Rodinal. This essentially forms a sodium paraminophenolate-ascorbate developer that you can play with while you're having phun.