For short: Use Rodinal at 16°C, with longer development time. The factor is around 1.6.
However because of the free Hydroxide in Rodinal poor temperature control across the process cycle can result in micro reticulation, the hydroxide softens the emulsion, it can be worse at higher temperatures as the swell of gelatin is also temperature related working a lower temperatures can cover up bad technique. The results of micro reticulation which is a surface effect is more apparent graininess in prints and scans, but the actual film grain is normal.
Agfa used to recommend mixing up Rodinal with a weak sulphite solution if you needed to prolong the life of a working solution this also helps give finer grain.
I have not tried them myself, but other folks have and say they work.
Wow, thank you all for the tips and advice. I couldn't believe my eyes when I checked the thread tonight. :)
For the record, I like grain. It gives my photo's a look that I like. Just slightly smaller than golf balls would be nice though. ;)
Changing to another film would be a bit awkward at the moment as I just spent 50 quid on a 30m roll of HP5+. Another developer would be interesting though.
Now going to have a read of the links.
If you're open to changing developers, I will suggest Xtol 1+1 or 1+2. Much less grainy than Rodinal, but with less loss of resolution/sharpness from solvent effects than you would get with D76. You'll also get at least one stop more film speed. It's definitely a different look than Rodinal and you may not like it, but it WILL help reduce the obtrusiveness of the grain. Or you might like it; who knows.
Using Xtol doesn't make the grains smaller, it reduces their intensity. If you think of grain noise as being a wave (variations in density with respect to position), then Xtol reduces the amplitude of the wave, not the wavelength.
I do think there are probably some "improvement" to be had by switching to XTol, DD-X, D-76, or Perceptol BUT it isn't even close to what a film change would get you AND finer grain means less sharpness, you can have one or the other. Only you can decide which is more important.
So, onward to considering the example shot you provided, why not just step closer to your subject?
Cut the distance by half or 2/3 (with the same focal length) and you have instantly reduced the size of the grain in relation to your subject matter by half or 2/3.
Finer grain doesn't mean less sharpness, in fact it often means better definition and sharpness on a macro level, but a grainy print might have more apparent sharpness from a distance.
Stand development is definitely going to be the way to go here. I'd try 1:100 for an hour. 15 seconds of slow agitation, then swoosh it (like you would a glass of fine wine) three times at the 20 and 40 minute mark. Temperature doesn't matter too much with stand, but keep it in the 20 degree celsius range. I've never done HP5 with stand, but I can imagine it'll work similary to Tri-X.
So Ian, it was my understanding that for a given film, fine grain developers essentially make a slightly softer images than high sharpness developers. For example that XTol used straight would produce finer grain than XTol at 1:4 because at 1:4 it has less solvent effect to smooth the edges. Am I off in that thinking?