This applies to any lens in any format for cameras or enlargers so I wasn't sure where to post it.
I've always thought of diffraction as an unfortunate fact of life for photographers, a limitation in light gathering, which cannot be corrected for. To me, this was presumably why a theoretically perfect optical formula is said to be "diffraction-limited" - ie in any lens diffraction increases as the aperture decreases in size. So I always thought of diffraction as being strictly/mathematically related somehow to the size of the circle through which light passes. Maybe the focal length has something to do with it, not sure.
Recently though I came across a lens test in one of the magazines (unfortunately I can't remember which magazine or which lens, but it was pretty recent) in which the lens in question was compared to alternate offerings from other manufacturers, and one of the comments made in favor of this lens was that diffraction was better controlled at smaller apertures. I'd never come across a statement like that before so I'm puzzled. How is diffraction controlled in the first place? Besides the aperture size, what are the factors? For example, is it something in the optics, or perhaps something with the diaphragm itself - rounder? thinner blades?