I usually work with 35 mm TX400 and HC110, E concentration (1:47) at 20ªC. The developer time is 6 minutes. Do you know how the grain size would change if I work with a higher dilution (1:63, for example). I am looking for a very small grain photo in order to print in 12 x 16 Ilford paper.
Like most things, it depends. When you dilute developer, you do a handful of things. You dilute any solvents in the developer. You change the pH a bit. You lengthen development time. Etc. When you sort it all out (that is, when you finally sit down and do the actual testing required to learn how it actually works) you'll likely find out that dilution will increase graininess a bit, and increase sharpness a bit. The combined effect in the final print is often very difficult to detect. I found, for example, that I needed to go to about 15x enlargement to see the difference in the final print between Tri-X in HC-110B, and Tri-X in HC-110H. But since I never enlarge beyond about 12x, I can't actually see it in my final prints.
This leads to people like me saying that the primary reason to dilute developer is to control development time.
I also want to ask suggestions for another film and/or developer combo in order to get no grain. I am thinking in Tmax 400 (probably at EI 250) with an appropriate developer.
Without grain, there *is* no image. Resign yourself to grain; it's a *requirement* of using film.
That said, the things you can do to minimize grain, in order of importance (and of course, IMHO):
1) Go up in format size.
2) Choose a smaller grain film (that is, slower).
3) Choose a t-grain film.
4) Choose a solvent developer (my personal favorite: XTOL)
There are more, but beyond these the effects drop off markedly. These are, IMHO, the "biggies."
Personally, I use 5x4 TMY-2 in XTOL. I'm stunned every sheet of film I pull. It's hard to believe that photography can be this good.