(120 film) Tri X 400 @ 6400

Paulo, ID-11 is very similar to D-76, so I would start with numbers you find for that developer.

I'd strongly recommend using another developer, if at all possible. I tried D-76/ID-11 many times over the years for push processing and the results were consistently mediocre at best with Tri-X pushed beyond 1600.

If at all possible, try to get some Ilford Microphen, Ilfotec DD-X; Kodak Xtol, TMax or HC-110 developer; Acufine or something better suited to extreme push processing. I've personally had consistently good results with Microphen, but other photographers here and elsewhere have reported good results with DD-X, Xtol, TMax, Acufine and others. HC-110 gave me better results than D-76/ID-11 for pushing.

If ID-11 is all you have available, pushing T-Max 400 or Tri-X to 6400 is voodoo and guesswork at best so any recommended times will be of dubious value (including my own). Results will depend more on exposure and how soon you develop the film. See my comments in this recent thread for additional background: Shot a roll of T-MAX P3200 at 6400...

If I shot a roll of those films at 6400, and had access only to ID-11, I'd first:

• Start with one test roll.
• Refrigerate or freeze the other rolls.
• Use undiluted ID-11 stock solution.
• Develop for at least 30 minutes.
• Agitate normally for the first 5 minutes.
• After the first 5 minutes, increase the interval time between agitations to every 2-5 minutes.

Regarding the modified agitation, this is a modified version of "stand development". In theory, this helps compensate for the extremes between the highlight areas and very thin underexposed areas (sometimes referred to as shadow detail, but in reality there will be no shadow detail at all in ISO 400 films pushed to 6400). If it works, the contrast will be more reasonable.

In actual practice, there are valid reasons to doubt whether any compensation effect occurs, but that's a digression. The main risk is uneven development and streaking. But when I've tried this type of modified stand development - 5 minutes of normal agitation followed by longer intervals between agitations - I saw no streaking, bromide drag, etc.

After developing one test roll, you'll be in a better position to decide whether to develop the remaining rolls similarly.

However, keep in mind that it's essential to develop this film promptly. Even after a month you'll lose a significant amount of the latent image.

I developed a roll of Tri-x (35mm) at 6400 and developed in Rodinal 1+100 for an hour:

Not saying it was awesome, but it did work.

Thank you for the great tips. Lex... you answer is a mind blowing flow of information, thank you for that. I made some essays with the negatives and I think they came out... charming.
I can't really hope for any detailed, sharp image, but being from a rock concert I think I can get away with "charming". :)
I'll try to post some samples in this answer.
The first two images were developed in ID-11, stock, 20ºC, for 19 minutes. It needed a lot more development time.

The rest of the images were developed in ID-11, 1:1, 20ºC for 25 minutes. These came out much, much better and I like the outcome. Tonight I'm trying 30 minutes.

Thank you again guys, you are great.

First try: Kodak Trix 400@6400.
ID-11, stock, 20ºC, 19 min.

Second try: Kodak Trix 400@6400.
ID-11, 1:1, 20ºC, 25 min.

Third try: Kodak Trix 400@6400.
ID-11, 1:1, 20ºC, 25 min.

Fourth try: Kodak Trix 400@6400. ID-11, 1:1, 20ºC, 25 min.

Those look good, Paulo. I really like the look of pushed b&w for most performance and stage photos. It helps isolate the desired subjects from backgrounds that are often cluttered and distracting.

I'm looking forward to seeing your other results from this sessions. It'll be interesting to see whether additional development helps.

By the way, how did you meter for these photos? Most performance situations I've encountered range from around EV 4-7 at best. That's a challenge with medium format cameras since lenses faster than f/2.8 are rare. I've tended to avoid using medium format for this type of photography, but I might give it a try again.