Jos, I don't have an extension tube that narrow, only a 20mm or so. How do you put this whole operation together? Camera mounted on downward facing tripod, enlarger stand, or what? Film holder from 35mm enlarger, improvised from scratch, or what? Diffuser from plastic milk bottle, special frosted glass, or what? Light from a light box, flash, or what? The devil is in the details, as my weeks of trying to put something together has shown me. I'm running out of patience and ready cash trying to cobble something together!
Oh, and I'm not sure what you mean by noise. The graininess in the V600 flatbed's image is actually visible, in blurry form, on the DSLR images, so I'm assuming it is actually present in the film as grain and not just noise. I'd be happy to see it in the DSLR images! And I only have an 11.5X magnifier. The onscreen blowups are taking about 0.2" on the neg and blowing it up to about 7", or 35X.