Ektar 25 professional was the only colour film in an enlarger, that you could never find grain with a grain focuser.
Instead we used different objects, like lines or a colour change and by focusing on a colour change area, like a red strip of material which had a blue colour abutting it.
It was an incredibly fine grained film.
We enlarged a 35mm film frame that had a full portrait of a person, we then did a straight enlargement to same size on a single sheet of paper. Mounted it onto 15mm foam core and placed it alongside the real person. This was for a Kodak Australasia advertisement.
It was very interesting to see a grainless picture with incredible detail at same size alongside the real life model.
This was used in Kodak seminars around the country, well at least in Melbourne, Sydney and Brisbane.