Rodinal could be used in many dilutions, from 1:10 to 1:200. Typically 1:50 is a good choice for normal, not to lengthy development with let say normal, every minute agitation. Film will have somewhat higher contrast than D76, grain should be moderate, but visible, lines should be sharp, sharper, than in D76. There is very valid reason for that. In 1:100, which was my standard dilution with Agfa APX 100 I achieved somewhat less contrasty negative, high sharpness and in 8X10 prints no visible grain. With 1:200 dilution, usually used for 35 -55 min stand development compensation should be achieved. What it means; while retaining good local microcontrast (good sharpness and detail) development of highlights (the dark part of the negative image which prints white or light gray on the paper) is slowed down preventing blocking the light during printing but development of shadows continues to reveal the detail which with standard development would be not achieved. Grain might be more visible, but it is nice looking grain, unlike D76, which produces rather ugly grain. (There is a good reason for it to.) Prints from Rodinal developed negatives usually are more contrasty, some say they display brilliance, while prints , if you used D76, have softer tonality, but also nice.
Why it is so ? It depends on two elements of the developer, the developing agent and activator. Rodinal is using p-Aminophenol Hydrochloride as a developing agent and Sodium Hydroxide, a strong base, as an activator. D76 is using metol and hydroquinone in borax. Rodinal works in pH 10 and up, borax produces something like pH 8.2 max. General contrast of the negative or print depends very much on pH. Metol in Sodium Hydroxide would also give more contrast. Then comes third element, preservative. In D76 there is 100 grams of sodium sulfit per liter, Rodinal contain 50 grams of Potassium Metabisulfite in 0>5 liter of concentrate. The difference is sodium sulfit not only prevents meto; from instant oxidation, also dissolves metallic silver, the builder of the image. Potassium Metabisulfite does it only marginally. And here is a secret of nice looking Rodinal grain versus spongy from D76. Take a look at this pictures, see the grain:
Book Nook | Photography Forum
And here my print.
Photographed with Imperial Reflex, extremely primitive, false TLR from 1960. Yet I like softness of this single element, meniscus lens. LOL
Acros 100 developed in BM2100 X-ray film developer. I discovered, that dental suppliers still carry chemicals for X-ray and they are very cheap, but top quality. LOL For $25 I have 8 liters of concentrate, for this film I used 45 ml. I have enough for over 170 rolls of 120 film. Another $25 buys 8 liters of fixer concentrate...
Colour of this picture is no accident, print was made on warm paper and I developed for that warmth. Almost sepia.
Links:
Photographic Chemical Descriptions
General Notes: Photographic Formulas
Digitaltruth Photo - Photographic Chemical Formulas and Technical Data
This for starters as it really never ends. LOL.
Cheers.